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My interests here at the Textbook-Wiki are in the natural sciences.

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Organic Chemistry/Cover

Welcome to the world's foremost open content  Organic Chemistry Textbook   on the web!

The Study of Organic Chemistry
Organic chemistry is primarily devoted to the unique properties of the carbon atom and its compounds. These compounds play a critical role in biology and ecology, Earth sciences and geology, physics, industry, medicine and — of course — chemistry. At first glance, the new material that organic chemistry brings to the table may seem complicated and daunting, but all it takes is concentration and perseverance. Millions of students before you have successfully passed this course and you can too!

This field of chemistry is based less on formulas and more on reactions between various molecules under different conditions. Whereas a typical general chemistry question may ask a student to compute an answer with an equation from the chapter that they memorized, a more typical organic chemistry question is along the lines of "what product will form when substance X is treated with solution Y and bombarded by light". The key to learning organic chemistry is to understand it rather than cram it in the night before a test. It is all well and good to memorize the mechanism of Michael addition, but a superior accomplishment would be the ability to explain why such a reaction would take place.

As in all things, it is easier to build up a body of new knowledge on a foundation of solid prior knowledge. Students will be well served by much of the knowledge brought to this subject from the subject of General Chemistry. Concepts with particular importance to organic chemists are covalent bonding, Molecular Orbit theory, VSEPR Modeling, understanding acid/base chemistry vis-a-vis pKa values, and even trends of the periodic table. This is by no means a comprehensive list of the knowledge you should have gained already in order to fully understand the subject of organic chemistry, but it should give you some idea of the things you need to know to succeed in an organic chemistry test or course.

Organic Chemistry is one of the subjects which are very useful and close to our daily life. We always try to figure out some of the unknown mysteries of our daily life through our factious thinking habit, which generates superstitions. Through the help of chemistry we can help ourselves to get out of this kind of superstition. We always try to find the ultimate truth through our own convenience. In the ancient past we had struggled to make things to go as per our need. In that context we have found fire, house, food, transportation, etc...

Now the burning question is: "how can chemistry help our daily life?" To find the answer of this questions, we have to know the subject thoroughly. Let us start it from now.

title: Organic Chemistry/Cover


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Organic Chemistry/Foundational concepts of organic chemistry

The purpose of this section is to review topics from freshman chemistry and build the foundation for further studies in organic chemistry.

 * 1) History of organic chemistry
 * 2) Atomic structure
 * 3) Electronegativity
 * 4) Bonding
 * 5) Electron dot structures
 * 6) Visualization
 * 7) Resonance
 * 8) Acids and bases
 * 9) Nomenclature

| Alkanes >>


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Organic Chemistry/Introduction to reactions

> Introduction to reactions

> Introduction to reactions

Specific Reactions

 * 1) Polar and radical reactions
 * 2) Redox reactions
 * 3) Carbocations
 * 4) Hydroboration/oxidation
 * 5) Free-radical halogenation
 * 6) Rearrangement reactions
 * 7) Pericyclic reactions
 * 8) Diels-Alder reaction


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Organic Chemistry/Alkenes

<< Haloalkanes |Alkenes| Alkynes >>

Alkenes are aliphatic hydrocarbons containing carbon-carbon double bonds and general formula CnH2n.

=Naming Alkenes= Alkenes are named as if they were alkanes, but the "-ane" suffix is changed to "-ene". If the alkene contains only one double bond and that double bond is terminal (the double bond is at one end of the molecule or another) then it is not necessary to place any number in front of the name.

butane: C4H10 (CH3CH2CH2CH3) butene: C4H8 (CH2=CHCH2CH3)

If the double bond is not terminal (if it is on a carbon somewhere in the center of the chain) then the carbons should be numbered in such a way as to give the first of the two double-bonded carbons the lowest possible number, and that number should precede the "ene" suffix with a dash, as shown below.

correct: pent-2-ene (CH3CH=CHCH2CH3) incorrect: pent-3-ene (CH3CH2CH=CHCH3) The second one is incorrect because flipping the formula horizontally results in a lower number for the alkene.

If there is more than one double bond in an alkene, all of the bonds should be numbered in the name of the molecule - even terminal double bonds. The numbers should go from lowest to highest, and be separated from one another by a comma. The IUPAC numerical prefixes are used to indicate the number of double bonds.

octa-2,4-diene: CH3CH=CHCH=CHCH2CH2CH3 deca-1,5-diene: CH2=CHCH2CH2CH=CHCH2CH2CH2CH3

Note that the numbering of "2-4" above yields a molecule with two double bonds separated by just one single bond. Double bonds in such a condition are called "conjugated", and they represent an enhanced stability of conformation, so they are energetically favored as reactants in many situations and combinations.

EZ Notation
Earlier in stereochemistry, we discussed cis/trans notation where cis- means same side and trans- means opposite side. Alkenes can present a unique problem, however in that the cis/trans notation sometimes breaks down. The first thing to keep in mind is that alkenes are planar and there's no rotation of the bonds, as we'll discuss later. So when a substituent is on one side of the double-bond, it stays on that side.

The above example is pretty straight-forward. On the left, we have two methyl groups on the same side, so it's cis-but-2-ene. And on the right, we have them on opposite sides, so we have trans-but-2-ene. So in this situation, the cis/trans notation works and, in fact, these are the correct names.

From the example above, how would you use cis and trans? Which is the same side and which is the opposite side? Whenever an alkene has 3 or 4 differing substituents, one must use the what's called the EZ nomenclature, coming from the German words, Entgegen (opposite) and Zusammen (same).

Let's begin with (Z)-3-methylpent-2-ene. We begin by dividing our alkene into left and right halves. On each side, we assign a substituent as being either a high priority or low priority substituent. The priority is based on the atomic number of the substituents. So on the left side, hydrogen is the lowest priority because its atomic number is 1 and carbon is higher because its atomic number is 6.

On the right side, we have carbon substituents on both the top and bottom, so we go out to the next bond. On to the top, there's another carbon, but on the bottom, a hydrogen. So the top gets high priority and the bottom gets low priority.

Because the high priorities from both sides are on the same side, they are Zusammen (as a mnemonic, think 'Zame Zide').

Now let's look at (E)-3-methylpent-2-ene. On the left, we have the same substituents on the same sides, so the priorities are the same as in the Zusammen version. However, the substituents are reversed on the right side with the high priority substituent on the bottom and the low priority substituent on the top. Because the High and Low priorities are opposite on the left and right, these are Entgegen, or opposite.

The system takes a little getting used to and it's usually easier to name an alkene than it is to write one out given its name. But with a little practice, you'll find that it's quite easy.

Comparison of E-Z with cis-trans
To a certain extent, the Z configuration can be regarded as the cis- isomer and the E as the trans- isomers. This correspondence is exact only if the two carbon atoms are identically substituted.

In general, cis-trans should only be used if each double-bonded carbon atom has a hydrogen atom (i.e. R-CH=CH-R').

IUPAC Gold book on cis-trans notation.

IUPAC Gold book on E-Z notation.

=Properties=

Alkenes are molecules with carbons bonded to hydrogens which contain at least two sp2 hybridized carbon atoms. That is, to say, at least one carbon-to-carbon double bond, where the carbon atoms, in addition to an electron pair shared in a sigma (σ) bond, share one pair of electrons in a pi (π) bond between them.

The general formula for an aliphatic alkene is: CnH2n -- e.g. C2H4 or C3H6

Restricted rotation
Because of the characteristics of pi-bonds, alkenes have very limited rotation around the double bonds between two atoms. In order for the alkene structure to rotate the pi-bond would first have to be broken - which would require about 60 or 70 kcal of energy per mol. For this reason alkenes have different chemical properties based on which side of the bond each atom is located.

For example, but-2-ene exists as two diastereomers:

=Relative stability= Observing the reaction of the addition of hydrogen to 1-butene, (Z)-2-butene, and (E)-2-butene, we can see that all of the products are butane. The difference between the reactions is that each reaction has a different energy: -30.3 kcal/mol for 1-butene, -28.6 kcal/mol for (Z)-2-butene and -27.6 kcal/mol for (E)-2-butene. This illustrates that there are differences in the stabilities of the three species of butene isomers, due to the difference in how much energy can be released by reducing them.

The relative stability of alkenes may be estimated based on the following concepts:
 * An internal alkene (the double bond not on the terminal carbon) is more stable than a terminal alkene (the double bond is on a terminal carbon).

Internal alkenes are more stable than terminal alkenes because they are connected to more carbons on the chain. Since a terminal alkene is located at the end of the chain, the double bond is only connected to one carbon, and is called primary (1°). Primary carbons are the least stable. In the middle of a chain, a double bond could be connected to two carbons. This is called secondary (2°). The most stable would be quaternary (4°).

 * In general, the more and the bulkier the alkyl groups on a sp2-hybridized carbon in the alkene, the more stable that alkene is.

 * A trans double bond is more stable than a cis double bond.

=Reactions=

Preparation
There are several methods for creating alkenes. Some of these methods, such as the Wittig reaction, we'll only describe briefly in this chapter and instead, cover them in more detail later in the book. For now, it's enough to know that they are ways of creating alkenes.

Dehydrohalogenation of Haloalkanes

Alkyl halides are converted into alkenes by dehydrohalogenation: elimination of the elements of hydrogen halide. Dehydrohalogenation involves removal of the halogen atom together with a hydrogen atom from a carbon adjacent to the one bearing the halogen. It uses the E2 elimination mechanism that we'll discuss in detail at the end of this chapter The haloalkane must have a hydrogen and halide 180° from each other on neighboring carbons. If there is no hydrogen 180° from the halogen on a neighboring carbon, the reaction will not take place. It is not surprising that the reagent required for the elimination of what amounts to a molecule of acid is a strong base for example: alcoholic KOH.

In some cases this reaction yields a single alkene. and in other cases yield a mixture. n-Butyl chloride, for example, can eliminate hydrogen only from C-2 and hence yields only 1-butene. sec-Butyl chloride, on the other hand, can eliminate hydrogen from either C-l or C-3 and hence yields both 1-butene and 2-butene. Where the two alkenes can be formed, 2-butene is the chief product.

Dehalogenation of Vicinal Dihalides

The dehalogenation of vicinal dihalides (halides on two neighboring carbons, think "vicinity") is another method for synthesizing alkenes. The reaction can take place using either sodium iodide in a solution of acetone, or it can be performed using zinc dust in a solution of either heated ethanol or acetic acid.

This reaction can also be performed with magnesium in ether, though the mechanism is different as this actually produces, as an intermediate, a Grignard reagent that reacts with itself and causes an elimination, resulting in the alkene.

Dehydration of alcohols
An alcohol is converted into an alkene by dehydration: elimination of a molecule of water. Dehydration requires the presence of an acid and the application of heat. It is generally carried out in either of two ways, heating the alcohol with sulfuric or phosphoric acid to temperatures as high as 200, or passing the alcohol vapor over alumina, Al2O3, at 350-400, alumina here serving as a Lewis acid.

Ease of dehydration of alcohols : 3° > 2° > 1°

Where isomeric alkenes can be formed, we again find the tendency for one isomer to predominate. Thus, sec-butyl alcohol, which might yield both 2-butene and 1-butene, actually yields almost exclusively the 2-isomer

The formation of 2-butene from n-butyl alcohol illustrates a characteristic of dehydration that is not shared by dehydrohalogenalion: the double bond can be formed at a position remote from the carbon originally holding the -OH group. This characteristic is accounted for later. It is chiefly because of the greater certainty as to where the double bond will appear that dehydrohalogeation is often preferred over dehydration as a method of making alkenes.

Reduction of Alkynes
Reduction of an alkyne to the double-bond stage can yield either a cis-alkene or a trans-alkene, unless the triple bond is at the end of a chain. Just which isomer predominates depends upon the choice of reducing agent.

Predominantly trans-alkene is obtained by reduction of alkynes with sodium or lithium in liquid ammonia. Almost entirely cis-alkene (as high as 98%) is obtained by hydrogenation of alkynes with several different catalysts : a specially prepared palladium called Lindlar's catalyst; or a nickel boride called P-2 catalyst.

Each of these reactions is, then, highly stereoselective. The stereoselectivity in the cis-reduction of alkynes is attributed, in a general way, to the attachment of two hydrogens to the same side of an alkyne sitting on the catalyst surface; presumably this same stereochemistry holds for the hydrogenation of terminal alkynes which cannot yield cis- and trans-alkenes.

Markovnikov's Rule
Before we continue discussing reactions, we need to take a detour and discuss a subject that's very important in Alkene reactions, "Markovnikov's Rule." This is a simple rule stated by the Russian Vladmir Markovnikov in 1869, as he was showing the orientation of addition of HBr to alkenes.

His rule states:"When an unsymmetrical alkene reacts with a hydrogen halide to give an alkyl halide, the hydrogen adds to the carbon of the alkene that has the greater number of hydrogen substituents, and the halogen to the carbon of the alkene with the fewer number of hydrogen substituents" (This rule is often compared to the phrase: "The rich get richer and the poor get poorer." Aka, the Carbon with the most Hydrogens gets another Hydrogen and the one with the least Hydrogens gets the halogen)

This means that the nucleophile of the electrophile-nucleophile pair is bonded to the position most stable for a carbocation, or partial positive charge in the case of a transition state.

Examples
$$ CH_2=CH-CH_3 + H-Br -> CH3-CHBr-CH_3 $$ Here the Br attaches to the middle carbon over the terminal carbon, because of Markovnikov's rule, and this is called a Markovnikov product.

Markovnikov product
The product of a reaction that follows Markovnikov's rule is called a Markovnikov product.

Markovnikov addition
Markovnikov addition is an addition reaction which follows Markovnikov's rule, producing a Markovnikov product.

Anti-Markovnikov addition
Certain reactions produce the opposite of the Markovnikov product, yielding what is called anti-Markovnikov product. That is, hydrogen ends up on the more substituted carbon of the double bond. The hydroboration/oxidation reaction that we'll discuss shortly, is an example of this, as are reactions that are conducted in peroxides.

A modernized version of Markovnikov's rule often explains the "anti-Markovnikov" behavior. The original Markovnikov rule predicts that the hydrogen (an electrophile) being added across a double bond will end up on the carbon with more hydrogens. Generalizing to all electrophiles, it is really the electrophile which ends up on the carbon with the greatest number of hydrogens. Usually hydrogen plays the role of the electrophile; however, hydrogen can also act as an nucleophile in some reactions. The following expansion of Markovnikov's rule is more versatile:

"When an alkene undergoes electrophilic addition, the electrophile adds to the carbon with the greatest number of hydrogen substituents. The nucleophile adds to the more highly substituated carbon."

Or more simply:

"The species that adds first adds to the carbon with the greatest number of hydrogens."

The fact that some reactions reliably produce anti-Markovnikov products is actually a powerful tool in organic chemistry. For example, in the reactions we discuss below, we'll show two different ways of creating alcohols from alkenes: Oxymercuration-Reduction and Hydroboration/Oxidation. Oxymercuration produces a Markovnikov product while Hydroboration produces an anti-Markovnikov product. This gives the organic chemist a choice in products without having to be stuck with a single product that might not be the most desired.

Why it works
Markovnikov's rule works because of the stability of carbocation intermediates. Experiments tend to reveal that carbocations are planar molecules, with a carbon that has three substituents at 120° to each other and a vacant p orbital that is perpendicular to it in the 3rd plane. The p orbital extends above and below the trisubstituent plane.

This leads to a stabilizing effect called hyperconjugation. Hyperconjugation is what happens when there is an unfilled (antibonding or vacant) C-C π orbital and a filled C-H σ bond orbital next to each other. The result is that the filled C-H σ orbital interacts with the unfilled C-C π orbital and stabilizes the molecule. The more highly substituted the molecule, the more chances there are for hyperconjugation and thus the more stable the molecule is.

Another stabilizing effect is an inductive effect.

Exceptions to the Rule
There are a few exceptions to the Markovnikov rule, and these are of tremendous importance to organic synthesis.

 * 1) HBr in Hydrogen Peroxide: Due to formation of free radicals, and the mechanism in which it reacts, the alkyl free radical forms at the middle atom, where it is most stable, and a hydrogen attaches itself here. Note here hydrogen addition is the second step, unlike in the above example.

Hydroboration
Hydroboration is a very useful reaction in Alkenes, not as an end product so much as an intermediate product for further reactions. The primary one we'll discuss below is the Hydroboration/Oxidation reaction which is actually a hydroboration reaction followed by a completely separate oxidation reaction.

The addition of BH3 is a concerted reaction in that several bonds are broken and formed at the same time. Hydroboration happens in what's called syn-addition because the boron and one of its hydrogens attach to the same side of the alkene at the same time. As you can see from the transition state in the center of the image, this produces a sort of box between the two alkene carbons and the boron and its hydrogen. In the final step, the boron, along with its other two hydrogens, remains attached to one carbon and the other hydrogen attaches to the adjacent carbon.

This description is fairly adequate, however, the reaction actually continues to happen and the -BH2 continue to react with other alkenes giving an R2BH and then again, until you end up with a complex of the boron atom attached to 3 alkyl groups, or R3B.

This trialkyl-boron complex is then used in other reactions to produce various products.

Borane, in reality, is not stable as BH3. Boron, in this configuration has only 6 electrons and wants 8, so in its natural state it actually creates the B2H6 complex shown on the left.

Furthermore, instead of using B2H6 itself, BH3 is often used in a complex with tetrahydrofuran (THF) as shown in the image on the right.In either situation, the result of the reactions are the same.

Hydroboration/Oxidation

With the reagent diborane, (BH3)2, alkenes undergo hydroboration to yield alkylboranes, R3B, which on oxidation give alcohols.The reaction procedure is simple and convenient, the yields are exceedingly high, and the products are ones difficult to obtain from alkenes in anyother way.

Diborane is the dimer of the hypothetical BH3 (borane) and, in the reactions that concern us, acts much as though it were BH3. Indeed, in tetrahydrofuran, one of the solvents used for hydroboration, the reagent exists as the monomer, in the form of an acid-base complex with the solvent.

Hydroboration involves addition to the double bond of BH3 (or, in following stages, BH2R and BHR2), with hydrogen becoming attached to one doubly-bonded carbon, and boron to the other. The alkylborane can then undergo oxidation, in which the boron is replaced by -OH.

Thus, the two-stage reaction process of hydroboration-oxidation permits, in effect, the addition to the carbon-carbon double bond of the elements of H-OH.

Reaction is carried out in an ether, commonly tetrahydrofuran or "diglyme" (diethylene glycol methyl ether, CH3OCH2CH2OCH2CH2OCH3). Diborane is commercially available in tetrahydrofuran solution. The alkylboranes are not isolated, but are simply treated in situ with alkaline hydrogen peroxide.

Stereochemistry and Orientation
Hydroboration-oxidation, then, converts alkenes into alcohols. Addition is highly regiospecific; the preferred product here, however, is exactly opposite to the one formed by oxymercuration-demercuration or by direct acid-catalyzed hydration.

The hydroboration-oxidation process gives products corresponding to anti-Markovnikov addition of water to the carbon-carbon double bond.

The reaction of 3,3-dimethyl-l -butene illustrates a particular advantage of the method. Rearrangement does not occur in hydroboration evidently because carbonium ions are not intermediates and hence the method can be used without the complications that often accompany other addition reactions. The reaction of 1,2-dimethylcyclopentene illustrates the stereochemistry of the synthesis: hydroboration-oxidation involves overall syn addition.

Oxymercuration/Reduction

Alkenes react with mercuric acetate in the presence of water to give hydroxymercurial compounds which on reduction yield alcohols.

The first stage, oxymercuration, involves addition to the carbon-carbon double bond of -OH and -HgOAc. Then, in reduction, the -HgOAc is replaced by -H. The reaction sequence amounts to hydration of the alkene, but is much more widely applicable than direct hydration.

The two-stage process of oxymercuration/reduction is fast and convenient, takes place under mild conditions, and gives excellent yields often over 90%. The alkene is added at room temperature to an aqueous solution of mercuric acetate diluted with the solvent tetrahydrofuran. Reaction is generally complete within minutes. The organomercurial compound is not isolated but is simply reduced in situ by sodium borohydride, NaBH4. (The mercury is recovered as a ball of elemental mercury.)

Oxymercuration/reduction is highly regiospecific, and gives alcohols corresponding to Markovnikov addition of water to the carbon-carbon double bond.

Oxymercuration involves electrophilic addition to the carbon-carbon double bond, with the mercuric ion acting as electrophile. The absence of rearrangement and the high degree of stereospecificity (typically anti) in the oxymercuration step argues against an open carbonium ion as intermediate. Instead, it has been proposed, there is formed a cyclic mercurinium ion, analogous to the bromonium and chloronium ions involved in the addition of halogens. In 1971, Olah reported spectroscopic evidence for the preparation of stable solutions of such mercurinium ions.

The mercurinium ion is attacked by the nucleophilic solvent water, in the present case to yield the addition product. This attack is back-side (unless prevented by some structural feature) and the net result is anti addition, as in the addition of halogens. Attack is thus of the SN2 type; yet the orientation of addition shows that the nucleophile becomes attached to the more highly substituted carbon as though there were a free carbonium ion intermediate. As we shall see, the transition state in reactions of such unstable threemembered rings has much SN1 character.

Reduction is generally not stereospecific and can, in certain special cases, be accompanied by rearrangement.

Despite the stereospecificity of the first stage, then, the overall process is not,in general, stereospecific. Rearrangements can occur, but are not common. The reaction of 3,3-dimethyl-1-butene illustrates the absence of the rearrangements that are typical of intermediate carbonium ions.

Diels-Alder Reaction
The Diels–Alder reaction is a reaction (specifically, a cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system. The reaction can proceed even if some of the atoms in the newly formed ring are not carbon. Some of the Diels–Alder reactions are reversible; the decomposition reaction of the cyclic system is then called the retro-Diels–Alder.

The Diels–Alder reaction is generally considered one of the more useful reactions in organic chemistry since it requires very little energy to create a cyclohexene ring, which is useful in many other organic reactions

A concerted, single-step mechanism is almost certainly involved; both new carbon-carbon bonds are partly formed in the same transition state, although not necessarily to the same extent. The Diels-Alder reaction is the most important example of cycloaddition. Since reaction involves a system of 4 π electrons (the diene) and a system of 2 π it electrons (the dienophile), it is known as a [4 + 2] cycloaddition.

Catalytic addition of hydrogen
Catalytic hydrogenation of alkenes produce the corresponding alkanes. The reaction is carried out under pressure in the presence of a metallic catalyst. Common industrial catalysts are based on platinum, nickel or palladium, but for laboratory syntheses, Raney nickel (formed from an alloy of nickel and aluminium) is often employed.

The catalytic hydrogenation of ethylene to yield ethane proceeds thusly:
 * CH2=CH2 + H2 + catalyst → CH3-CH3

Electrophilic addition
Most addition reactions to alkenes follow the mechanism of electrophilic addition. An example is the Prins reaction, where the electrophile is a carbonyl group.

Halogenation
Addition of elementary bromine or chlorine in the presence of an organic solvent to alkenes yield vicinal dibromo- and dichloroalkanes, respectively.

The decoloration of a solution of bromine in water is an analytical test for the presence of alkenes: CH2=CH2 + Br2 → BrCH2-CH2Br

The reaction works because the high electron density at the double bond causes a temporary shift of electrons in the Br-Br bond causing a temporary induced dipole. This makes the Br closest to the double bond slightly positive and therefore an electrophile.

Hydrohalogenation
Addition of hydrohalic acids like HCl or HBr to alkenes yield the corresponding haloalkanes.

 * an example of this type of reaction is: CH3CH=CH2 + HBr → CH3-CHBr-CH3

If the two carbon atoms at the double bond are linked to a different number of hydrogen atoms, the halogen is found preferentially at the carbon with less hydrogen substituents (Markovnikov's rule).

Addition of a carbene or carbenoid yields the corresponding cyclopropane

Oxidation
Alkenes are oxidized with a large number of oxidizing agents. In the presence of oxygen, alkenes burn with a bright flame to form carbon dioxide and water. Catalytic oxidation with oxygen or the reaction with percarboxylic acids yields epoxides.

Reaction with ozone in ozonolysis leads to the breaking of the double bond, yielding two aldehydes or ketones: R1-CH=CH-R2 + O3 → R1-CHO + R2-CHO + H2O

This reaction can be used to determine the position of a double bond in an unknown alkene.

Polymerization
Polymerization of alkenes is an economically important reaction which yields polymers of high industrial value, such as the plastics polyethylene and polypropylene. Polymerization can either proceed via a free-radical or an ionic mechanism.

=Substitution and Elimination Reaction Mechanisms=

Nucleophilic Substitution Reactions
Nucleophilic substitution reactions (SN1 and SN2) are very closely related to the E1 and E2 elimination reactions, discussed later in this section, and it is generally a good idea to learn the reactions together, as there are parallels in reaction mechanism, preferred substrates, and the reactions sometimes compete with each other.

It's important to understand that substitution and elimination reactions are not associated with a specific compound or mixture so much as they're a representation of how certain reactions take place. At times, combinations of these mechanisms may occur together in the same reaction or may compete against each other, with influences such as solvent or nucleophile choice being the determining factor as to which reaction will dominate.

In nucleophilic substitution, a nucleophile attacks a molecule and takes the place of another nucleophile, which then leaves. The nucleophile that leaves is called the leaving group.

Nucleophilic substitutions require
 * 1) a nucleophile (such as a Lewis base)
 * 2) an electrophile with a leaving group

A leaving group is a charged or neutral moiety (group) which breaks free.

SN1 vs SN2
One of the main differences between SN1 and SN2 is that the SN1 reaction is a 2-step reaction, initiated by disassociation of the leaving group. The SN2 reaction, on the other hand, is a 1-step reaction where the attacking nucleophile, because of its higher affinity for and stronger bonding with the carbon, forces the leaving group to leave. These two things happen in a single step.

These two different mechanisms explain the difference in reaction rates between SN1 and SN2 reactions. SN1 reactions are dependent on the leaving group disassociating itself from the carbon. It is the rate-limiting step and thus, the reaction rate is a first-order reaction whose rate depends solely on that step.

 * $$Rate = k[RX]$$

Alternatively, in SN2 reactions, the single step of the nucleophile coming together with the reactant from the opposite side of the leaving group, is the key to its rate. Because of this, the rate is dependent on both the concentration of the nucleophile as well as the concentration of the reactant. The higher these two concentrations, the more frequent the collisions. Thus the reaction rate is a second-order reaction:

 * $$Rate = k[Nu:][RX]$$ (where Nu: is the attacking nucleophile)

SN2 Reactions
There are primarily 3 things that affect whether an SN2 reaction will take place or not. The most important is structure. That is whether the alkyl halide is on a methyl, primary, secondary, or tertiary carbon. The other two components that determine whether an SN2 reaction will take place or not, are the nucleophilicity of the nucleophile and the solvent used in the reaction.

The structure of the alkyl halide has a great effect on mechanism. CH3X & RCH2X are the preferred structures for SN2. R2CHX can undergo the SN2 under the proper conditions (see below), and R3CX rarely, if ever, is involved in SN2 reactions.

The reaction takes place by the nucleophile attacking from the opposite side of the bromine atom. Notice that the other 3 bonds are all pointed away from the bromine and towards the attacking nucleophile. When these 3 bonds are hydrogen bonds, there's very little steric hinderance of the approaching nucleophile. However, as the number of R groups increases, so does the steric hinderance, making it more difficult for the nucleophile to get close enough to the α-carbon, to expel the bromine atom. In fact, tertiary carbons (R3CX) are so sterically hindered as to prevent the SN2 mechanism from taking place at all.

In the case of this example, a secondary α-carbon, there is still a great deal of steric hinderance and whether the SN2 mechanism will happen will depend entirely on what the nucleophile and solvent are. SN2 reactions are preferred for methyl halides and primary halides.

Another important point to keep in mind, and this can be seen clearly in the example above, during an SN2 reaction, the molecule undergoes an inversion. The bonds attached to the α-carbon are pushed away as the nucleophile approaches. During the transition state, these bonds become planar with the carbon and, as the bromine leaves and the nucleophile bonds to the α-carbon, the other bonds fold back away from the nucleophile. This is particularly important in chiral or pro-chiral molecules, where an R configuration will be converted into an S configuration and vice versa. As you'll see below, this is in contrast to the results of SN1 reactions.

Examples:

 * OH- + CH3—Cl → HO—CH3 + Cl-

OH- is the nucleophile, Cl is the electrophile, HOCH3 is the product, and Cl- is the leaving group.

or,

 * Na+I- + CH3-Br → I-CH3 + Na+Br-

The above reaction, taking place in acetone as the solvent, sodium and iodide disassociate almost completely in the acetone, leaving the iodide ions free to attack the CH-Br molecules. The negatively charged iodide ion, a nucleophile, attacks the methyl bromide molecule, forcing off the negatively charged bromide ion and taking its place. The bromide ion is the leaving group.

Nucleophilicity
Nucleophilicity is the rate at which a nucleophile displaces the leaving group in a reaction. Generally, nucleophilicity is stronger, the larger, more polarizable, and/or the less stable the nucleophile. No specific number or unit of measure is used. All other things being equal, nucleophiles are generally compared to each other in terms of relative reactivity. For example, a particular strong nucleophile might have a relative reactivity of 10,000 that of a particular weak nucleophile. These relationships are generalities as things like solvent and substrate can affect the relative rates, but they are generally good guidelines for which species make the best nucleophiles.

All nucleophiles are Lewis bases. In SN2 reactions, the preferred nucleophile is a strong nucleophile that is a weak base. Examples of these are N3-, RS-, I-, Br-, and CN-.

Alternatively, a strong nucleophile that's also a strong base can also work. However, as mentioned earlier in the text, sometimes reaction mechanisms compete and in the case of a strong nucleophile that's a strong base, the SN2 mechanism will compete with the E2 mechanism. Examples of strong nucleophiles that are also strong bases, include RO- and OH-.

Leaving Group
Leaving group is the group on the substrate that leaves. In the case of an alkyl halide, this is the halide ion that leaves the carbon atom when the nucleophile attacks. The tendency of the nucleophile to leave is

Fluoride ions are very poor leaving groups because they bond very strongly and are very rarely used in alkyl halide substitution reactions. Reactivity of a leaving group is related to its basicity with stronger bases being poorer leaving groups.

Solvent
The solvent can play an important role in SN2 reactions, particularly in SN2 involving secondary alkyl halide substrates, where it can be the determining factor in mechanism. Solvent can also have a great effect on reaction rate of SN2 reactions.

The SN2 mechanism is preferred when the solvent is an aprotic, polar solvent. That is, a solvent that is polar, but without a polar hydrogen. Polar, protic solvents would include water, alcohols, and generally, solvents with polar NH or OH bonds. Good aprotic, polar solvents are HMPA, CH3CN, DMSO, and DMF.

A polar solvent is preferred because it better allows the dissociation of the halide from the alkyl group. A protic solvent with a polar hydrogen, however, forms a 'cage' of hydrogen-bonded solvent around the nucleophile, hindering its approach to the substrate.

SN1 Reactions
The SN1 mechanism is very different from the SN2 mechanism. In some of its preferences, its exactly the opposite and, in some cases, the results of the reaction can be significantly different.

Like the SN2 mechanism, structure plays an important role in the SN1 mechanism. The role of structure in the SN1 mechanism, however, is quite different and because of this, the reactivity of structures is more or less reversed.

The SN1 mechanism is preferred for tertiary alkyl halides and, depending on the solvent, may be preferred in secondary alkyl halides. The SN1 mechanism does not operate on primary alkyl halides or methyl halides. To understand why this is so, let's take a look at how the SN1 mechanism works.

At the top of the diagram, the first step is the spontaneous dissociation of the halide from the alkyl halide. Unlike the SN2 mechanism, where the attacking nucleophile causes the halide to leave, the SN1 mechanism depends on the ability of the halide to leave on its own. This requires certain conditions. In particular, the stability of the carbocation is crucial to the ability of the halide to leave. Since we know tertiary carbocations are the most stable, they are the best candidates for the SN1 mechanism. And with appropriate conditions, secondary carbocations will also operate by the SN1 mechanism. Primary and methyl carbocations however, are not stable enough to allow this mechanism to happen.

Once the halide has dissociated, the water acts as a nucleophile to bond to the carbocation. In theSN2 reactions, there is an inversion caused by the nucleophile attacking from the opposite side while the halide is still bonded to the carbon. In the SN1 mechanism, since the halide has left, and the bonds off of the α-carbon have become planar, the water molecule is free to attack from either side. This results in, primarily, a racemic mixture. In the final step, one of the hydrogens of the bonded water molecule is attacked by another water molecule, leaving an alcohol.

''Note: Racemic mixtures imply entirely equal amounts of mixture, however this is rarely the case in SN1. There is a slight tendency towards attack from the opposite side of the halide. This is the result some steric hinderence from the leaving halide which is sometimes close enough to the leaving side to block the nucleophile's approach from that side.''

Solvent
Like the SN2 mechanism, the SN1 is affected by solvent as well. As with structure, however, the reasons differ. In the SN1 mechanism, a polar, protic solvent is used. The polarity of the solvent is associated with the dielectric constant of the solvent and solutions with high dielectric constants are better able to support separated ions in solution. In SN2 reactions, we were concerned about polar hydrogen atoms "caging" our nucleophile. This still happens with a polar protic solvent in SN1 reactions, so why don't we worry about it? You have to keep in mind the mechanism of the reaction. The first step, and more importantly, the rate-limiting step, of the SN1 reaction, is the ability to create a stable carbocation by getting the halide anion to leave. With a polar protic solvent, just as with a polar aprotic solvent,we're creating a stable cation, however it's the polar hydrogens that stabilize the halide anion and make it better able to leave. Improving the rate-limiting step is always the goal. The "caging" of the nucleophile is unrelated to the rate-limiting step and even in its "caged" state, the second step, the attack of the nucleophile, is so much faster than the first step, that the "caging" can simply be ignored.

Summary
SN1, SN2, E1, and E2, are all reaction mechanisms, not reactions themselves. They are mechanisms used by a number of different reactions. Usually in organic chemistry, the goal is to synthesize a product. In cases where you have possibly competing mechanisms, and this is particularly the case where an SN1 and an E1 reaction are competing, the dominating mechanism is going to decide what your product is, so knowing the mechanisms and which conditions favor one over the other, will determine your product.

In other cases, knowing the mechanism allows you to set up an environment favorable to that mechanism. This can mean the difference between having your product in a few minutes, or sometime around the next ice age.

So when you're designing a synthesis for a product, you need to consider, I want to get product Y, so what are my options to get to Y? Once you know your options and you've decided on a reaction, then you need to consider the mechanism of the reaction and ask yourself, how do I create conditions that are going to make this happen correctly and happen quickly?

Elimination Reactions
Nucleophilic substitution reactions and Elimination reactions share a lot of common characteristics, on top of which, the E1 and SN1 as well as E2 and SN2 reactions can sometimes compete and, since their products are different, it's important to understand them both. Without understanding both kinds of mechanisms, it would be difficult to get the product you desire from a reaction.

In addition, the SN1 and SN2 reactions will be referenced quite a bit by way of comparison and contrast, so it's probably best to read that section first and then continue here.

Elimination reactions are the mechanisms for creating alkene products from haloalkane reactants. E1 and E2 elimination, unlike SN1 and SN2 substitution, mechanisms do not occur with methyl halides because the reaction creates a double bond between two carbon atoms and methylhalides have only one carbon.

Reaction rates
E1 and E2 are two different pathways to creating alkenes from haloalkanes. As with SN1 and SN2 reactions, one of the key differences is in the reaction rate, as it provides great insight into the mechanisms.

E1 reactions, like SN1 reactions are 2-step reactions. Also like SN1 reactions, the rate-limiting step is the dissociation of the halide from its alkane, making it a first-order reaction, depending on the concentration of the haloalkane, with a reaction rate of:

 * $$Rate = k[RX]$$

On the other hand, E2 reactions, like SN2 reactions are 1-step reactions. And again, as with SN2 reactions, the rate limiting step is the ability of a nucleophile to attach to the alkane and displace the halide. Thus it is a second-order reaction that depends on the concentrations of both the nucleophile and haloalkane, with a reaction rate of:

 * $$Rate = k[Nu:][RX]$$ (where Nu: is the attacking nucleophile)

Zaitsev's Rule
Zaitsev's rule (sometimes spelled "Saytzeff") states that in an elimination reaction, when multiple products are possible, the most stable alkene is the major product. That is to say, the most highly substituted alkene (the alkene with the most non-hydrogen substituents) is the major product.

Both E1 and E2 reactions produce a mixture of products, when possible, but generally follow Zaitsev's rule. We'll see below why E1 reactions follow Zaitsev's rule more reliably and tend to produce a purer product.

The above image represents two possible pathways for the dehydrohalogenation of (S)-2-bromo-3-methylbutane. The two potential products are 2-methylbut-2-ene and 3-methylbut-1-ene. The images on the right are simplified drawings of the molecular product shown in the images in the center.

As you can see on the left, the bromine is on the second carbon and in an E1 or E2 reaction, the hydrogen could be removed from either the 1st or the 3rd carbon. Zaitsev's rule says that the hydrogen will be removed predominantly from the 3rd carbon. In reality, there will be a mixture, but most of the product will be 2-methylbut-2-ene by the E1 mechanism. By the E2 reaction, as we'll see later, this might not necessarily be the case.

E2
The E2 mechanism is concerted and highly stereospecific, because it can occur only when the H and the leaving group X are in an anti-coplanar position. That is, in a Newman projection, the H and X must be 180°, or in the anti-configuration. This behaviour stems from the best overlap of the 2p orbitals of the adjacent carbons when the pi bond has to be formed. If the H and the leaving group cannot be brought into this position due to the structure of the molecule, the E2 mechanism will not take place.

Therefore, only molecules having accessible H-X anti-coplanar conformations can react via this route. Furthermore, the E2 mechanism will operate contrary to Zaitsev's rule if the only anti-coplanar hydrogen from the leaving group results in the least stable alkene. A good example of how this can happen is by looking at how cyclohexane and cyclohexene derivatives might operate in E2 conditions.

Let's look at the example above. The reactant we're using is 1-chloro-2-isopropylcyclohexane. The drawing at the top left is one conformation and the drawing below is after a ring flip. In the center are Newman projections of both conformations and the drawings on the right, the products.

If we assume we're treating the 1-chloro-2-isopropylcyclohexane with a strong base, for example CH3CH2O- (ethanolate), the mechanism that dominates is E2. There are 3 hydrogens off of the carbons adjacent to our chlorinated carbon. The red and the green ones are two of them. The third would be hard to show but is attached to the same carbon as the red hydrogen, angled a little down from the plane and towards the viewer. The red hydrogen is the only hydrogen that's 180° from the chlorine atom, so it's the only one eligible for the E2 mechanism. Because of this, the product is going to be only 3-isopropylcylcohex-1-ene. Notice how this is contrary to Zaitsev's rule which says the most substituted alkene is preferred. By his rule, 1-isopropylcyclohexene should be our primary product, as that would leave the most substituted alkene. However it simply can't be produced because of the steric hindrance.

The images below shows the molecule after a ring flip. In this conformation, no product is possible. As you can see from the Newman projection, there are no hydrogens 180° from the chlorine atom.

So it's important, when considering the E2 mechanism, to understand the geometry of the molecule. Sometimes the geometry can be used to your advantage to preferentially get a single product. Other times it will prevent you from getting the product you want, and you'll need to consider a different mechanism to get your product.

''Note: Often the word periplanar is used instead of coplanar. Coplanar implies precisely 180 degree separation and "peri-", from Greek for "near", implies near 180 degrees. Periplanar may actually be more accurate. In the case of the 1-chloro-3-isopropylcyclohexane example, because of molecular forces, the chlorine atom is actually slightly less than 180 degrees from both the hydrogen and the isopropyl group, so in this case, periplanar might be a more correct term.''

E1

The E1 mechanism begins with the dissociation of the leaving group from an alkyl, producing a carbocation on the alkyl group and a leaving anion. This is the same way the SN1 reaction begins, so the same thing that helps initiate that step in SN1 reactions, help initiate the step in E1 reactions. More specifically, secondary and tertiary carbocations are preferred because they're more stable than primary carbocations. The choice of solvent is the same as SN1 as well; a polar protic solvent is preferred because the polar aspect stabilizes the carbocation and the protic aspect stabilizes the anion.

What makes the difference between whether the reaction takes the SN1 or E1 pathway then, must depend on the second step; the action of the nucleophile. In SN1 reactions, a strong nucleophile that's a weak base is preferred. The nucleophile will then attack and bond to the carbocation. In E1 reactions, a strong nucleophile is still preferred. The difference is that a strong nucleophile that's also a strong base, causes the nucleophile to attack the hydrogen at the β-carbon instead of the α-carbocation. The nucleophile/base then extracts the hydrogen causing the bonding electrons to fall in and produce a pi bond with the carbocation.

Because the hydrogen and the leaving group are lost in two separate steps and the fact that it has no requirements as to geometry, the E1 mechanism more reliably produces products that follow Zaitsev's rule.

=References=

<< Haloalkanes |Alkenes| Alkynes >>

title: Organic Chemistry/Alkenes


text:
Organic Chemistry/Chirality

Introduction
Chirality (pronounced kie-RAL-it-tee) is the property of handedness. If you attempt to superimpose your right hand on top of your left, the two do not match up in the sense that your right hand's thumb overlays your left hand's pinky finger. Your two hands cannot be superimposed identically, despite the fact that your fingers of each hand are connected in the same way. Any object can have this property, including molecules.

An object that is chiral is an object that can not be superimposed on its mirror image. Chiral objects don't have a plane of symmetry. An achiral object has a plane of symmetry or a rotation-reflection axis, i.e. reflection gives a rotated version.

Optical isomers or enantiomers are stereoisomers which exhibit chirality. Optical isomerism is of interest because of its application in inorganic chemistry, organic chemistry, physical chemistry, pharmacology and biochemistry.

They are often formed when asymmetric centers are present, for example, a carbon with four different groups bonded to it. Every stereocenter in one enantiomer has the opposite configuration in the other.

When a molecule has more than one source of asymmetry, two optical isomers may be neither perfect reflections of each other nor superimposeable: some but not all stereocenters are inverted. These molecules are an example of diastereomers: They are not enantiomers. Diastereomers seldom have the same physical properties. Sometimes, the stereocentres are themselves symmetrical. This causes the counterintuitive situation where two chiral centres may be present but no isomers result. Such compounds are called meso compounds.

A mixture of equal amounts of both enantiomers is said to be a racemic mixture.

It is the symmetry of a molecule (or any other object) that determines whether it is chiral or not. Technically, a molecule is achiral (not chiral) if and only if it has an axis of improper rotation; that is, an n-fold rotation (rotation by 360°/n) followed by a reflection in the plane perpendicular to this axis which maps the molecule onto itself. A chiral molecule is not necessarily dissymmetric (completely devoid of symmetry) as it can have, e.g., rotational symmetry. A simplified rule applies to tetrahedrally-bonded carbon, as shown in the illustration: if all four substituents are different, the molecule is chiral.

It is important to keep in mind that molecules which are dissolved in solution or are in the gas phase usually have considerable flexibility and thus may adopt a variety of different conformations. These various conformations are themselves almost always chiral. However, when assessing chirality, one must use a structural picture of the molecule which corresponds to just one chemical conformation – the one of lowest energy.

Chiral Compounds With Stereocenters
Most commonly, chiral molecules have point chirality, centering around a single atom, usually carbon, which has four different substituents. The two enantiomers of such compounds are said to have different absolute configurations at this center. This center is thus stereogenic (i.e., a grouping within a molecular entity that may be considered a focus of stereoisomerism), and is exemplified by the α-carbon of amino acids.

The special nature of carbon, its ability to form four bonds to different substituents, means that a mirror image of the carbon with four different bonds will not be the same as the original compound, no matter how you try to rotate it. Understanding this is vital because the goal of organic chemistry is understanding how to use tools to synthesize a compound with the desired chirality, because a different arrangement may have no effect, or even an undesired one.

A carbon atom is chiral if it has four different items bonded to it at the same time. Most often this refers to a carbon with three heteroatoms and a hydrogen, or two heteroatoms plus a bond to another carbon plus a bond to a hydrogen atom. It can also refer to a nitrogen atom bonded to four different types of molecules, if the nitrogen atom is utilizing its lone pair as a nucleophile. If the nitrogen has only three bonds it is not chiral, because the lone pair of electrons can flip from one side of the atom to the other spontaneously.

Any atom in an organic molecule that is bonded to four different types of atoms or chains of atoms can be considered "chiral".

If a carbon atom (or other type of atom) has four different substituents, that carbon atom forms a chiral center (also known as a stereocenter). Chiral molecules often have one or more stereocenters. When drawing molecules, stereocenters are usually indicated with an asterisk near the carbon.

Example:

Left: The carbon atom has a Cl, a Br, and 2 CH3. That's only 3 different substituents, which means this is not a stereocenter.

Center: The carbon atom has one ethyl group (CH2CH3), one methyl group (CH3) and 2 H. This is not a stereocenter.

Right: The carbon atom has a Cl and 1 H. Then you must look around the ring. Since one side has a double bond and the other doesn't, it means the substituents off that carbon are different. The 4 different substituents make this carbon a stereocenter and makes the molecule chiral.

A molecule can have multiple chiral centers without being chiral overall: It is then called a meso compound. This occurs if there is a symmetry element (a mirror plane or inversion center) which relates the chiral centers.

Fischer projections
Fischer projections (after the German chemist Hermann Emil Fischer) are an ingenious means for representing configurations of carbon atoms. Considering the carbon atom as the center, the bonds which extend towards the viewer are placed horizontally. Those extending away from the viewer are drawn vertically. This process, when using the common dash and wedge representations of bonds, yields what is sometimes referred to as the "bowtie" drawing due to its characteristic shape. This representation is then further shorthanded as two lines: the horizontal (forward) and the vertical (back), as showed in the figure below:

Operations on Fischer projections

 * in a Fischer projection, exchange two substituent positions results in the inversion of the stereocenter
 * rotation by 90° of the Fischer projection results in inversion
 * rotation by 180° of the Fischer projection preserves the configuration

Naming conventions
There are three main systems for describing configuration: the oldest, the relative whose use is now deprecated, and the current, or absolute. The relative configuration description is still used mainly in glycochemistry. Configuration can also be assigned on the purely empirical basis of the optical activity.

By optical activity: (+)- and (-)-
An optical isomer can be named by the direction in which it rotates the plane of polarized light. If an isomer rotates the plane clockwise as seen by a viewer towards whom the light is traveling, that isomer is labeled (+). Its counterpart is labeled (-). The (+) and (-) isomers have also been termed d- and l-, respectively (for dextrorotatory and levorotatory). This labeling is easy to confuse with D- and L- and is therefore not encouraged by IUPAC.

The fact that an enantiomer can rotate polarised light clockwise (d- or +- enantiomer) does not relate with the relative configuration (D- or L-) of it.

By relative configuration: D- and L-
Fischer, whose research interest was in carbohydrate chemistry, took glyceraldehyde (the simplest sugar, systematic name 2,3-dihydroxypropanal) as a template chiral molecule and denoted the two possible configurations with D- and L-, which rotated polarised light clockwise and counterclockwise, respectively.

All other molecules are assigned the D- or L- configuration if the chiral centre can be formally obtained from glyceraldehyde by substitution. For this reason the D- or L- naming scheme is called relative configuration.

An optical isomer can be named by the spatial configuration of its atoms. The D/L system does this by relating the molecule to glyceraldehyde. Glyceraldehyde is chiral itself, and its two isomers are labeled D and L. Certain chemical manipulations can be performed on glyceraldehyde without affecting its configuration, and its historical use for this purpose (possibly combined with its convenience as one of the smallest commonly-used chiral molecules) has resulted in its use for nomenclature. In this system, compounds are named by analogy to glyceraldehyde, which generally produces unambiguous designations, but is easiest to see in the small biomolecules similar to glyceraldehyde.

One example is the amino acid alanine: alanine has two optical isomers, and they are labeled according to which isomer of glyceraldehyde they come from. Glycine, the amino acid derived from glyceraldehyde, incidentally, does not retain its optical activity, since its central carbon is not chiral. Alanine, however, is essentially methylated glycine and shows optical activity.

The D/L labeling is unrelated to (+)/(-); it does not indicate which enantiomer is dextrorotatory and which is levorotatory. Rather, it says that the compound's stereochemistry is related to that of the dextrorotatory or levorotatory enantiomer of glyceraldehyde. Nine of the nineteen L-amino acids commonly found in proteins are dextrorotatory (at a wavelength of 589 nm), and D-fructose is also referred to as levulose because it is levorotatory.

The dextrorotatory isomer of glyceraldehyde is in fact the D isomer, but this was a lucky guess. At the time this system was established, there was no way to tell which configuration was dextrorotatory. (If the guess had turned out wrong, the labeling situation would now be even more confusing.)

A rule of thumb for determining the D/L isomeric form of an amino acid is the "CORN" rule. The groups:

 * COOH, R, NH2 and H (where R is an unnamed carbon chain)

are arranged around the chiral center carbon atom. If these groups are arranged clockwise around the carbon atom, then it is the L-form. If counter-clockwise, it is the D-form.This rule only holds when the hydrogen atom is pointing out of the page.

By absolute configuration: R- and S-
Main article: R-S System

The absolute configuration system stems from the Cahn-Ingold-Prelog priority rules, which allow a precise description of a stereocenter without using any reference compound. In fact the basis is now the atomic number of the stereocenter substituents.

The R/S system is another way to name an optical isomer by its configuration, without involving a reference molecule such as glyceraldehyde. It labels each chiral center R or S according to a system by which its ligands are each assigned a priority, according to the Cahn Ingold Prelog priority rules, based on atomic number.

This system labels each chiral center in a molecule (and also has an extension to chiral molecules not involving chiral centers). It thus has greater generality than the D/L system, and can label, for example, an (R,R) isomer versus an (R,S) — diastereomers.

The R/S system has no fixed relation to the (+)/(-) system. An R isomer can be either dextrorotatory or levorotatory, depending on its exact ligands.

The R/S system also has no fixed relation to the D/L system. For example, one of glyceraldehyde's ligands is a hydroxy group, -OH. If a thiol group, -SH, were swapped in for it, the D/L labeling would, by its definition, not be affected by the substitution. But this substitution would invert the molecule's R/S labeling, due to the fact that sulfur's atomic number is higher than carbon's, whereas oxygen's is lower. [Note: This seems incorrect. Oxygen has a higher atomic number than carbon. Sulfur has a higher atomic number than oxygen. The reason the assignment priorities change in this example is because the CH2SH group gets a higher priority than the CHO, whereas in glyceraldehyde the CHO takes priority over the CH2OH.]

For this reason, the D/L system remains in common use in certain areas, such as amino acid and carbohydrate chemistry. It is convenient to have all of the common amino acids of higher organisms labeled the same way. In D/L, they are all L. In R/S, they are not, conversely, all S — most are, but cysteine, for example, is R, again because of sulfur's higher atomic number.

The word “racemic” is derived from the Latin word for grape; the term having its origins in the work of Louis Pasteur who isolated racemic tartaric acid from wine.

Chiral Compounds Without Stereocenters
It is also possible for a molecule to be chiral without having actual point chirality (stereocenters). Commonly encountered examples include 1,1'-bi-2-naphthol (BINOL) and 1,3-dichloro-allene which have axial chirality, and (E)-cyclooctene which has planar chirality.

For example, the isomers which are shown by the following figure are different. The two isomers cannot convert from one to another spontaneously because of restriction of rotation of double bonds.

Other types of chiral compounds without stereocenters (like restriction of rotation of a single bond because of steric hindrance) also exist. Consider the following example of the R and S binol molecules:

The biphenyl C-C bond cannot rotate if the X and Y groups cause steric hindrance.

This compound exhibits spiral chirality.

Properties of optical isomers
Enantiomers have – when present in a symmetric environment – identical chemical and physical properties except for their ability to rotate plane-polarized light by equal amounts but in opposite directions. A solution of equal parts of an optically-active isomer and its enantiomer is known as a racemic solution and has a net rotation of plane-polarized light of zero.

Enantiomers differ in how they interact with different optical isomers of other compounds. In nature, most biological compounds (such as amino acids) occur as single enantiomers. As a result, different enantiomers of a compound may have substantially different biological effects. Different enantiomers of the same chiral drug can have very different pharmological effects, mainly because the proteins they bind to are also chiral.

For example, spearmint leaves and caraway seeds respectively contain L-carvone and D-carvone – enantiomers of carvone. These smell different to most people because our taste receptors also contain chiral molecules which behave differently in the presence of different enantiomers.

D-form Amino acids tend to taste sweet, whereas L-forms are usually tasteless. This is again due to our chiral taste molecules. The smells of oranges and lemons are examples of the D and L enantiomers.

Penicillin's activity is stereoselective. The antibiotic only works on peptide links of D-alanine which occur in the cell walls of bacteria – but not in humans. The antibiotic can kill only the bacteria, and not us, because we don't have these D-amino acids.

The electric and magnetic fields of polarized light oscillate in a geometric plane. An axis normal to this plane gives the direction of energy propagation. Optically active isomers rotate the plane that the fields oscillate in. The polarized light is actually rotated in a racemic mixture as well, but it is rotated to the left by one of the two enantiomers, and to the right by the other, which cancel out to zero net rotation.

Chirality in biology
Many biologically-active molecules are chiral, including the naturally-occurring amino acids (the building blocks of proteins), and sugars. Interestingly, in biological systems most of these compounds are of the same chirality: most amino acids are L and sugars are D. The origin of this homochirality in biology is the subject of much debate.

Chiral objects have different interactions with the two enantiomers of other chiral objects. Enzymes, which are chiral, often distinguish between the two enantiomers of a chiral substrate. Imagine an enzyme as having a glove-like cavity which binds a substrate. If this glove is right handed, then one enantiomer will fit inside and be bound while the other enantiomer will have a poor fit and is unlikely to bind.

Chirality in inorganic chemistry

Many coordination compounds are chiral; for example the well-known [Ru(2,2'-bipyridine)3]2+ complex in which the three bipyridine ligands adopt a chiral propeller-like arrangement [7]. In this case, the Ru atom may be regarded as a stereogenic centre, with the complex having point chirality. The two enantiomers of complexes such as [Ru(2,2'-bipyridine)3]2+ may be designated as Λ (left-handed twist of the propeller described by the ligands) and Δ (right-handed twist). Hexol is a chiral cobalt compound.

More definitions

 * Any non-racemic chiral substance is called scalemic
 * A chiral substance is enantiopure or homochiral when only one of two possible enantiomers is present.
 * A chiral substance is enantioenriched or heterochiral when an excess of one enantiomer is present but not to the exclusion of the other.
 * Enantiomeric excess or ee is a measure for how much of one enantiomer is present compared to the other. For example, in a sample with 40% ee in R, the remaining 60% is racemic with 30% of R and 30% of S, so that the total amount of R is 70%.

Enantiopure preparations
Several strategies exist for the preparation of enantiopure compounds. The first method is the separation of a racemic mixture into its isomers. Louis Pasteur in his pioneering work was able to isolate the isomers of tartaric acid because they crystallize from solution as crystals with differing symmetry. A less common and more recently discovered method is by enantiomer self-disproportionation, which is an advanced technique involving the separation of a primarily racemic fraction from a nearly enantiopure fraction via column chromatography.

In a non-symmetric environment (such as a biological environment) enantiomers may react at different speeds with other substances. This is the basis for chiral synthesis, which preserves a molecule's desired chirality by reacting it with or catalyzing it with chiral molecules capable of maintaining the product's chirality in the desired conformation (using certain chiral molecules to help it keep its configuration). Other methods also exist and are used by organic chemists to synthesize only (or maybe only mostly) the desired enantiomer in a given reaction.

Enantiopure medications
Advances in industrial chemical processes have allowed pharmaceutical manufacturers to take drugs that were originally marketed in racemic form and divide them into individual enantiomers, each of which may have unique properties. For some drugs, such as zopiclone, only one enantiomer (eszopiclone) is active; the FDA has allowed such once-generic drugs to be patented and marketed under another name. In other cases, such as ibuprofen, both enantiomers produce the same effects. Steroid receptor sites also show stereoisomer specificity.

Examples of racemic mixtures and enantiomers that have been marketed include:
 * Ofloxacin (Floxin) and Levofloxacin (Levaquin)
 * Bupivacaine (Marcaine) and Ropivacaine (Naropin)
 * Methylphenidate (Ritalin) and Dexmethylphenidate (Focalin)
 * Cetirizine (Zyrtec) and Levocetirizine (Xyzal)
 * Albuterol (Ventolin) and Levalbuterol (Xopenex)
 * Omeprazole (Prilosec) and Esomeprazole (Nexium)
 * Citalopram (Celexa / Cipramil) and Escitalopram (Lexapro / Cipralex)
 * Zopiclone (Imovane) and Eszopiclone (Lunesta)
 * Modafinil (Provigil) and Armodafinil (Nuvigil) — sulfur is the chiral center in modafinil, instead of carbon.

Many chiral drugs must be made with high enantiomeric purity due to potential side-effects of the other enantiomer. (The other enantiomer may also merely be inactive.)

Consider a racemic sample of thalidomide. One enantiomer was thought to be effective against morning sickness while the other is now known to be teratogenic. Unfortunately, in this case administering just one of the enantiomers to a pregnant patient would still be very dangerous as the two enantiomers are readily interconverted in vivo. Thus, if a person is given either enantiomer, both the D and L isomers will eventually be present in the patient's serum and so chemical processes may not be used to mitigate its toxicity.

title: Organic Chemistry/Chirality


text:
Organic Chemistry/Dienes

Organic chemistry > Dienes

<< Alkynes | Kinds of dienes >>

In alkene chemistry, we demonstrated that allylic carbon could maintain a cation charge because the double bond could de-localize to support the charge. What of having two double bonds separated by a single bond? What of having a compound that alternates between double bond and single bond? In addition to other concepts, this chapter will explore what a having a conjugated system means in terms of stability and reaction.

Dienes are simply hydrocarbons which contain two double bonds. Dienes are intermediate between alkenes and polyenes.

Dienes can divided into three classes:
 * Unconjugated dienes have the double bonds separated by two or more single bonds. These are also known as isolated dienes.
 * Conjugated dienes have conjugated double bonds separated by one single bond
 * Cumulated dienes (cumulenes) have the double bonds sharing a common atom as in a group of compounds called allenes.

 * 1) Kinds of dienes
 * 2) Conjugation
 * 3) Diene properties and reactions

<< Alkynes | Dienes | Aromatics >>

title: Organic Chemistry/Dienes


text:
Organic Chemistry/External links

Organic chemistry > Links to other online organic textbooks

=Resources=
 * The IUPAC Gold Book of definitions.

=Other online textbooks=
 * |url-status=dead|archive-url=https://ocw.mit.edu/courses/chemistry/5-12-organic-chemistry-i-spring-2003 MIT OpenCourseWare Organic Chemistry I (unfortunately, much of the information is in PDF documents instead of HTML).
 * Combinatorial Chemistry basic introduction to the field of combinatorial chemistry
 * MIT OpenCourseWare Organic Chemistry II (same PDF dilemma as above).
 * Virtual Text a real nice one by William Reusch of Michigan State University.
 * Crystal Clear Chemistry A good resource for studying and obtaining answers to conceptual questions that aren't answered elsewhere.
 * Chemhelper.com by student Arthur Winter of Frostburg State University.
 * LearnChem.net Helpful chemistry tutorials
 * Online version of a leading text Site extrapolating on parts of Francis Carey's leading textbook.
 * General chemistry reference at VisionLearning.com funded by National Science Foundation
 * Lab and other techniques compository
 * Organic Chemistry Portal
 * Organic chemistry resources worldwide
 * A full length, peer-reviewed, and free organic chemistry textbook. Can be downloaded in PDF format.
 * Khan Academy Colorful, clear and engaging Organic Chemistry video playlist.
 * Organic Chemistry Practice Problems A collection of organic chemistry practice problems with detailed video solutions.
 * Google search results

الكيمياء العضوية/قائمة المراجع

title: Organic Chemistry/External links


text:
User:Karl Wick

"Wikibooks co-founder." Started Wikibooks to bring down textbook  expense  and improve textbook  quality. Thank you to Wikipedia founder Jimbo Wales and everyone else who has already done much more than me to help further this dream. May Wikibooks provide the world free, top-quality textbooks!

title: User:Karl Wick


text:
User:Maveric149

en:user:maveric149

Nothing much to see here. Even though I'm a co-founder of Wikibooks and am the person who thought of the name, I pretty much only do admin and organization work here so far since most of my Wikimedia time is still spent on my various Wikipedia projects. However, I have dreamed of helping to start a project whereby instructors and other interested parties could collaboratively create educational materials for students for a long time. Now it is starting to happen!

Module note test

/Sandbox

Special:Makesysop

title: User:Maveric149


text:
Organic Chemistry/Foundational concepts of organic chemistry/History of organic chemistry

Atomic Structure >

Brief History
Jöns Jacob Berzelius, a physician by trade, first coined the term "organic chemistry" in 1806 for the study of compounds derived from biological sources. Up through the early 19th century, naturalists and scientists observed critical differences between compounds that were derived from living things and those that were not.

Chemists of the period noted that there seemed to be an essential yet inexplicable difference between the properties of the two different types of compounds. The vital force theory, sometimes called "vitalism" (vital means "life force"), was therefore proposed, and widely accepted, as a way to explain these differences, that a "vital force" existed within organic material but did not exist in any inorganic materials.

Synthesis of Urea
Friedrich Wöhler is widely regarded as a pioneer in organic chemistry as a result of his synthesizing of the biological compound urea (a component of urine in many animals) utilizing what is now called "the Wöhler synthesis."

Wöhler mixed silver or lead cyanate with ammonium nitrate; this was supposed to yield ammonium cyanate as a result of an exchange reaction, according to Berzelius's dualism theory. Wöhler, however, discovered that the end product of this reaction is not ammonium cyanate (NH4OCN), an inorganic salt, but urea ((NH2)2CO), a biological compound. (Furthermore, heating ammonium cyanate turns it into urea.) Faced with this result, Berzelius had to concede that (NH2)2CO and NH4OCN were isomers. Until this discovery in the year 1828, it was widely believed by chemists that organic substances could only be formed under the influence of the "vital force" in the bodies of animals and plants. Wöhler's synthesis dramatically proved that view to be false.

Urea synthesis was a critical discovery for biochemists because it showed that a compound known to be produced in nature only by biological organisms could be produced in a laboratory under controlled conditions from inanimate matter. This "in vitro" synthesis of organic matter disproved the common theory (vitalism) about the vis vitalis, a transcendent "life force" needed for producing organic compounds.

Organic vs Inorganic Chemistry
Although originally defined as the chemistry of biological molecules, organic chemistry has since been redefined to refer specifically to carbon compounds — even those with non-biological origin. Some carbon molecules are not considered organic, with carbon dioxide being the most well known and most common inorganic carbon compound, but such molecules are the exception and not the rule.

Organic chemistry focuses on carbon and following movement of the electrons in carbon chains and rings, and also how electrons are shared with other carbon atoms and heteroatoms. Organic chemistry is primarily concerned with the properties of covalent bonds and non-metallic elements, though ions and metals do play critical roles in some reactions.

The applications of organic chemistry are myriad, and include all sorts of plastics, dyes, flavorings, scents, detergents, explosives, fuels and many, many other products. Read the ingredient list for almost any kind of food that you eat — or even your shampoo bottle — and you will see the handiwork of organic chemists listed there.

Major Advances in the Field of Organic Chemistry
Of course a chemistry text should at least mention Antoine Laurent Lavoisier. The French chemist is often called the "Father of Modern Chemistry" and his place is first in any pantheon of great chemistry figures. Your general chemistry textbook should contain information on the specific work and discoveries of Lavoisier — they will not be repeated here because his discoveries did not relate directly to organic chemistry in particular. Berzelius and Wöhler are discussed above, and their work was foundational to the specific field of organic chemistry. After those two, three more scientists are famed for independently proposing the elements of structural theory. Those chemists were August Kekulé, Archibald Couper, and Alexander Butlerov.

Kekulé was a German, an architect by training, and he was perhaps the first to propose that isomerism was due to carbon's proclivity towards forming four bonds. Its ability to bond with up to four other atoms made it ideal for forming long chains of atoms in a single molecule, and also made it possible for the same number of atoms to be connected in an enormous variety of ways. Couper, a Scot, and Butlerov, a Russian, came to many of the same conclusions at the same time or just a short time after.

Through the nineteenth century and into the twentieth, experimental results brought to light much new knowledge about atoms, molecules, and molecular bonding. In 1916 it was Gilbert Lewis of U.C. Berkeley who described covalent bonding largely as we know it today (electron-sharing). Nobel laureate Linus Pauling further developed Lewis' concepts by proposing resonance while he was at the California Institute of Technology. At about the same time, Sir Robert Robinson of Oxford University focused primarily on the electrons of atoms as the engines of molecular change. Sir Christopher Ingold of University College, London, organized what was known of organic chemical reactions by arranging them in schemes we now know as mechanisms, in order to better understand the sequence of changes in a synthesis or reaction.

The field of organic chemistry is probably the most active and important field of chemistry at the moment, due to its extreme applicability to both biochemistry (especially in the pharmaceutical industry) and petrochemistry (especially in the energy industry). Organic chemistry has a relatively recent history, but it will have an enormously important future, affecting the lives of everyone around the world for many, many years to come.

<< Foundational concepts| History of Organic Chemistry | Atomic Structure > | Alkanes >>


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User:Nanobug

Michael Richards - Senior Systems Analyst and Programmer.

Why Nanobug? Take your pick:

 * I like the bugs in my programs to be very small.
 * I try not to bug people too much.
 * I have a bug for nanotechnology.

My page on Wikiquote, Wikipedia, Wiktionary, and Meta.

title: User:Nanobug


text:
Cookbook talk:Table of Contents

Why aren't there any links to Wikipedia pages?
I'm new to this project and I'd like to help, mainly by adding links, pics, and cleaning up. But I'm baffled as to why there are not links to Wikipedia on the Wikicookbook and vice-versa? Has there been a consensus regarding this issue? I added the links on Rhubarb Pie page, provisionally, until I hear otherwise. After, say, two weeks (is that a reasonable amount of time?), if there is no response, I'll start adding links to Wikipedia in a == See also == section. Is that ok? WikiUser70176 (discuss • contribs) 13:11, 3 April 2023 (UTC)

 * Hi @WikiUser70176 and welcome to the project! I am very active in the cookbook here and have been cleaning it up for the past year. According to Wikibooks policy, books are meant to be self-contained resources, and linking between books and to Wikipedia goes against best practices. Some external linking can be helpful when used judiciously, but I would say that it's not appropriate to do so without a very good reason. In many cases, external links are included when they would be more appropriate as citations or footnotes. You may also wish to take a look at Wikibooks for Wikimedians since you're coming from another project. Let me know if you have any questions. Cheers! —Kittycataclysm (discuss • contribs) 18:07, 3 April 2023 (UTC)
 * I would also note that in terms of recipe pictures, it's best to have pictures that were made using that specific recipe for the sake of accuracy and expectations. —Kittycataclysm (discuss • contribs) 18:16, 3 April 2023 (UTC)
 * Thanks so much! I understand the reasoning now, although it does take logic a bit to the extreme. Yes, a book is, a priori, a self-contained object. Nevertheless, a Wikibook is also a digital  book, so I'm thinking links should be allowed, as reading a hardcover book is fundamentally not the same as reading your screen. But, of course, I'll do what the consensus decided. Hopefully, the Wikipedia will allow me to put links to the Cookbook (see Rhubarb) WikiUser70176 (discuss • contribs) 18:26, 3 April 2023 (UTC)
 * @WikiUser70176 Happy to help! As far as I'm aware, it's completely fine (and very helpful!) to link to the Cookbook from Wikipedia, since Wikipedia acts as an encyclopedia and slightly more like a repository. My main understanding of the distinction is that Wikibooks is intended to serve a different function from Wikipedia, and there is a general desire to keep Wikibooks formatted somewhat differently to help underscore that function. I think that the intention is to keep Wikibooks from becoming a general repository and to maintain a sense of purpose and scope, but project veterans like @MarcGarver, @Xania, and @JackPotte may have a better explanation than I can provide. Cheers! —Kittycataclysm (discuss • contribs) 18:39, 3 April 2023 (UTC)
 * Hi, personally I just update Wikidata to help navigating between projects. But we probably need to update the bottom of Using Wikibooks/Wiki-Markup to answer to these kinds of interrogation. JackPotte (discuss • contribs) 21:12, 10 April 2023 (UTC)
 * Hi @JackPotte,
 * I have a question about links between the English wikibooks and wikidata: I was trying to find out how WD links items with a common name to ENWB. For example we have 3 pages of the cookbook about Apple Pies:
 * Cookbook: Apple Pie
 * Cookbook: Apple Pie I
 * Cookbook: Apple Pie II
 * I checked the WD item for Apple Pie and found out it links to Cookbook: Apple Pie I. I also checked to see who created this link and found out it was User:Wolverène who has never contributed to this wiki (I think?). In your opinion would it be wise to change the WD item to point to Cookbook: Apple Pie?
 * Thanks in advance, Ottawahitech (discuss • contribs) 22:46, 9 March 2024 (UTC)
 * There are a lot of issues with wikidata implementation at Wikibooks that have unfortunately not been resolved. However, I do think the WD item for apple pie would be better connected to Cookbook: Apple Pie rather than Cookbook: Apple Pie I. —Kittycataclysm (discuss • contribs) 22:49, 9 March 2024 (UTC)
 * Hello, I added the English link almost 6 years ago and I do not remember the context of my editing. There is no problem for me to change the connection into Cookbook:Apple Pie. --Wolverène (discuss • contribs) 07:08, 10 March 2024 (UTC)
 * Well, the initial problem was in interwikis which were included in the page. That is why I linked that in such a way. I have also created items for the apple pie recipes - d:Q124803141, d:Q124803154. However, I am not sure how to work properly on items for Wikibook pages (which properties fit better there, and such). Wikibooks are my grey area --Wolverène (discuss • contribs) 07:38, 10 March 2024 (UTC)

A newbie question

I have tried to find recipes I can handle. I am a terrible cook, but I love eating.

I find some of the recipes here awfully complex, and require a lot of pre-planning, at least for me. I have tried using this cookbook a coupe of times, just to find out half-way through that I a missing an essential element without which I cannot proceed. I have already learned to scan the list of ingredients ahead of time, but my trouble is the necessary equipment, such as a Muffin pan.

I realize it is very difficult to address an international audience who may have language difficulties, cultural objections to certain foods, food allergies, all on top of various levels of expertise. I just wonder if a section describing what is needed in terms of equipment can be added to all recipes?

Your comments are appreciated, Ottawahitech (discuss • contribs) 20:40, 24 January 2024 (UTC)

 * Hi @Ottawahitech! I'm glad you've been trying out the recipes, and I'm sorry you've had trouble. I do think it is reasonable to have an "equipment" section for recipes—some recipes already do, and the recipe template gives some additional guidance. It will take some time to adjust all the recipes accordingly, but please feel free to start doing so yourself if you're feeling up to it. Additionally, you might like to check out Category:Very Easy recipes and Category:Easy recipes. Cheers! —Kittycataclysm (discuss • contribs) 22:01, 24 January 2024 (UTC)

Why use the cookbook?
I have been trying out several recipes in this cookbook, some successfully others not so. Here is a question I have: Are there others here who are trying the recipes? Do we have any statistics to document this? How long has the cookbook been on wikibooks?

I am curious to find out why readers prefer to use this cookbook over other online recipe sources since we only use text while sources such as as YouTube have videos which the younger people in my real life use as the cooking-bible all the time. One advantage I can think of for WB is the fact that we allow comments on the talk-pages by IP-users who prefer anonymity and there are no commercials (other than the periodic donation pages), while on YouTube you can only participate in discussions if you have a google account which allows one to eliminate commercials, I think? Ottawahitech (discuss • contribs) 21:55, 9 March 2024 (UTC)

copyrights of menus
I made Cookbook:Rømmegrøt the other day. It is a Norwegian dish that I tasted for the first time many years ago but have not had recently. It is made with Cookbook:Homemade sour cream. It is not for those who watch their calories (does the cook book have a way of indicating this?). I found a recipe for it on the internet.

I understand that such things are copyrighted. How can I share this recipe with others?

Thanks in advance, Ottawahitech (discuss • contribs) 16:14, 12 March 2024 (UTC)

 * Hi @Ottawahitech! Regarding nutritional information, the cookbook does have Template:Nutrition Summary. Regarding the recipe, we cannot host any copyrighted content found elsewhere on the internet. If you find a recipe with a compatible license, or if you have a recipe of your own to share, we can take those. Cheers —Kittycataclysm (discuss • contribs) 22:32, 12 March 2024 (UTC)
 * Thanks for the reply, @Kittycataclysm. I was afraid of that.
 * I am not sure what makes a recipe one's own though, for copyrights' sake. People have been sharing recipes for millennia, so how can one determine whose "copyright" it is? If I use someone else's recipe but change apples to pears or use less sugar/ use an air-fryer to bake it instead of an oven/ bake it at 350 degrees for longer than another recipe that calls for 450 for a shorter period, the list goes on? and who is responsible for monetary damages if a copyrighted recipe is found at wikibooks? (I don't intend to do this, just wondering).
 * I also wonder how old the recipe must be before it becomes public property? I used own a 1950 cooking encyclopedia purchased at a garage sale which had some interesting recipes. What about recipes printed in government guides (nutrition related usually)?
 * Do we have copyrights experts at wikibooks? Thanks in advance, Ottawahitech (discuss • contribs) 00:41, 13 March 2024 (UTC)
 * Hi @Ottawahitech. You can find some more information on recipes and copyright at this external site. Generally, my understanding is that a simple list of ingredients or the idea of how to make something is not copyrightable, but the specific writing of the recipe is. Any copied written text of a recipe is therefore not accepted here. For specific legal expertise, you would have to contact WMF. —Kittycataclysm (discuss • contribs) 21:48, 21 March 2024 (UTC)
 * Offtopic: Shortly after I posted this I started getting online ads for (I think) a pill to reduce body fat. Coincidence I am sure. :-) Ottawahitech (discuss • contribs) 17:21, 21 April 2024 (UTC)

Is there an API for reading, adding, and editing recipes?
Hello, I make an aftermarket pellet grill controller that has a web app interface. I wanted to add a recipe section to the web app so users could add and edit their recipes directly from the app and share them with the world. The app can display the Cookbook wiki but it is a bit too complicated to add recipes using the templates. I am not a wiki expert so I may be missing another way to manage recipes. Any thoughts? Mcranepage (discuss • contribs) 13:53, 19 May 2024 (UTC)

 * Hi @Mcranepage! Are you asking if there's a way to add/edit Wikicookbook recipes directly from your web app? If I'm understanding correctly, you can read them but not edit them well—is that correct? —Kittycataclysm (discuss • contribs) 20:44, 19 May 2024 (UTC)
 * Hello, @Kittycataclysm, yes that is correct. My understanding of adding a recipe is that the user has to copy pieces of various recipe template parts, paste them into a new recipe page, figure out the right category(s) for the recipe, then there are a few visual editor type tools that he/she can use to edit the recipe parts before submitting it.  I was hoping to simplify the process by creating a form in the web app that the user could fill out then when he/she saves the recipe, the web app will send the recipe to the Cookbook wiki as an xml or json object.  I am open for suggestions. Mcranepage (discuss • contribs) 16:15, 20 May 2024 (UTC)
 * You can use mw:API:Edit to edit wikis. If you want users to edit in their own names (you probably should), you’ll also need OAuth/For Developers in a web app (or develop a gadget or user script instead, which runs on en.wikibooks.org and thus can directly edit in the current user’s name – even if the user isn’t logged in, which isn’t possible using OAuth). Of course, these are general APIs and don’t know anything about how the cookbook works, but if I understand correctly, you plan to write exactly the cookbook-specific parts anyway. —Tacsipacsi (discuss • contribs) 20:56, 20 May 2024 (UTC)
 * Hello @Tacsipacsi, Perfect! Thank you for the information. Mcranepage (discuss • contribs) 18:26, 21 May 2024 (UTC)

Omelette
Take two eggs and crack into bowl/cup add dried parsley leaves add into eggs,add a pinch of salt and pepper mix well add bread toast.

Light stove heat to medium temperature wait 3 minutes and flip put on low heat take a plate and take a cup and pour soda

Enjoy 😘

Tkzeemoondreamer07 (discuss • contribs) 08:47, 13 July 2024 (UTC)

title: Cookbook talk:Table of Contents


text:
User:Kpjas

Welcome to SLOVIO Pan-Slavic language

Vitajte vo SLOVIO Pan-slavju jazika

Go to Table of Contents >> Idijte do Table of Contents >>

title: User:Kpjas


text:
Wikibooks:Files to be harvested

This is a list of files that have been uploaded to serve as sources for text and images for the textbook project. Material from these can be used freely on this project.

Make sure you use other resources in a wise and legal way: Media

Organic Chemistry

 * [[media:SOCAWS9495.pdf|Organic chemistry basics]] (in German, but images can be useful)
 * Created & uploaded by Magnus Manske

Biochemistry

 * [[media:VBCAWS9798.doc|Biochemistry basics]] (in German, but images can be useful)
 * Created & uploaded by Magnus Manske

Various online references

 * List of mathematics texts including some with open content.
 * Other books, some free, some not - theassayer.org.
 * Public domain textbooks from the University of Pennsylvania. Lots of old ones here.
 * Dozens of online textbooks here although you'd have to investigate the license for each one.
 * Wikipedia has lots of useful GPL'ed information, though it needs to be assimilated and organized into a unified whole
 * Project Gutenberg has countless texts to which one could link

Getting permission

 * For the time being at least, we can only use outside material that is already CC-BY-SA licensed or in the public domain. However, experience on Wikipedia has shown that authors that place their work under one free license tend to be very willing to grant us a CC-BY-SA license, if we ask nicely. See: Boilerplate request for permission

title: Wikibooks:Files to be harvested


text:
User:Magnus Manske

Same guy as this one

I am working on the Biochemistry and Cell biology books here; maybe on Genetics as well, if anyone bothers...

Hi to you, too! What, only three books?? --RoseParks

title: User:Magnus Manske


text:
User:Juxo~enwikibooks

You will most likely find me at http://www.consumerium.org/wiki/wiki.phtml?title=User:Juxo

Wishlist
I'm really looking forward to someone with more expertise doing some Textbooks on the Unix. I think it would be a good idea to do it on a user story-basis. Wherein the structure would be case based so that it assumes you have a simple task to do and how to do it utilizing standard unix commands.

Here I'll be working on the Cookbook 'cause it happens to intersect with Consumerium nicely and besides I like good food :)

title: User:Juxo~enwikibooks


text:
Computer Programming/Authors

List of Authors
"You always need someone to blame."

 * The WikiCommunity
 * Martin Krischik (Contributions)
 * Josh Ferguson
 * Brian Mitchell
 * Gregory Pietsch
 * LittleDan for the XHTML tutorial
 * Kevin Whitefoot the more obscure parts of Programming:Visual Basic Classic

title: Computer Programming/Authors


text:
Cookbook:Policy/Recipe template

'''This is a template page. Please do not add recipes here .'''

This is the recommended template for recipes that are submitted to the cookbook. Please note that this is only a guideline; feel free to add other sections as necessary, or omit sections that are not applicable (although the recipe needs to be useful and comprehensible).

Various Cookbook-related templates can be found in the Cookbook policy module.

The five-dot system in the recipe summary is used to represent the relative difficulty of a recipe. Please keep these descriptions in mind when assigning a difficulty score. The images are useful in that clicking on them brings you to a category of recipes of particular difficulty. We borrowed these images from the German Cookbook (Kochbuch).

 * [[Image:1o5dots.svg|You can boil water, right?]] - Very easy; you can boil water, right?
 * [[Image:2o5dots.svg|Fairly easy]] - Easy
 * [[Image:3o5dots.svg|Medium difficulty]] - Average
 * [[Image:4o5dots.svg|Fairly hard]] - Hard
 * [[Image:5o5dots.svg|Are you the Iron Chef?]] - Very hard; are you the Iron Chef?

Include the recipe summary template  first, with image, cooking time, etc. Note the guidelines for the relative difficulty above. The image should be no more than 300px in order to maintain consistent style and formatting of all the Cookbook's recipe templates.

Follow with the recipe template, along with additional navigation links as appropriate: | Cuisine | Type of course

A short description of the recipe should go here; anywhere from one sentence to a paragraph or two is acceptable. Describe who uses the dish, and how, as well as anything normally prepared with it. Stories of the recipe's creation or other anecdotes are perfectly acceptable, but avoid first-person language to ensure NPOV and to reflect the communal nature of the Cookbook.

Ingredients
Ingredients may be listed as a list, like below: Alternatively, ingredients may be formatted as a table if it is more appropriate: The ingredients should be listed in the order they are called for in the procedure below. The ingredients should be linked to using the "pipe trick", i.e. Cookbook:carrot, which produces carrot. If optional ingredients and substitutions would make this list less readable, place them in the notes, tips, or variations section instead (if they are specific to some different cooking procedure) or place them in a second list after the first one. Otherwise, simply mark them "(optional)". Consider using separate lists for different components of the recipe.
 * 1 cup (240 ml) ingredient 1
 * 1 tablespoon (15 ml) ingredient 2
 * etc.

Quantities should be listed with whichever units (imperial or metric) the recipe was created in, with the other equivalent values listed immediately after, in "". This lets users know which units are "original" and which are estimated conversions. Avoid nested parentheses for legibility, instead separating units by a forward slash or the word 'or'. Always provide both volumetric and weight measurements—in some countries, kitchens are simply not equipped to measure by weight (yes, they lack a balance or scale). Do not specify the size of normal chicken eggs; "Large" in the USA is similar to "size M" in the EU, and other places will surely have their own ideas as well.

If a recipe does not list specific quantities, it must include sufficient information in the procedure to guide the cook on how much to add. This could be something like "according to taste", "until the mixture reaches _____ texture", etc.

Equipment
Details of needed equipment can be added here if desired. If you only list specialized equipment here as opposed to every utensil required to complete the recipe, change the heading to "Special equipment" to reflect this.

 * 1 mixing bowl
 * 1 mixing spoon
 * Baking paper
 * etc.

Procedure
The procedure should be written in numbered steps. Photos of the procedures as they are completed should be in |thumb| format, so a caption identifying what step is being performed can be included in the pic.

 * 1) Step one
 * 2) Step two
 * 3) etc.

Notes, tips, and variations
This area can be used for any additional information that doesn't fit in other areas of the recipe module. For significant variations, consider creating a new recipe page.

 * Note 1
 * Tip 1
 * Variation 1
 * etc.

Warnings
If the recipe requires it, add any necessary warnings here.
 * Warning 1
 * Warning 2
 * etc.

title: Cookbook:Policy/Recipe template