chemistry

Carbanions phenyl > cyclopropyl > ethyl > n-propyl > isobutyl > neopentyl > cyclobutyl > cyclopentyl References R. Bruckner, “Advanced Organic Chemistry – Reaction Mechanisms”, 2nd Edition, Elsevier, 2002 M.B. Smith & J. March “March’s Advanced Organic Chemistry”, 6th Edition, Wiley-Interscience, 2007 "/> Home > Organic Chemistry > Carbanions CARBANIONS Keto-Enol Tautomerism – Enolization – Reactions and Mechanism The chemistry of enolate ions – Reactions with alkyl halides   Carbanions are species with a complete octet around the carbon atom. A general formula of a carbanion is of the form:     By definition, every carbanion possesses an unshared pair of electrons and is therefore a base. When a carbanion accepts a proton, it is converted to its conjugate acid . The stability of a...

The chemistry of enolate ions – Enolate ion reactions with alkyl halides The chemistry of enolate ions – Alkylations - Enolate ion reactions with alkyl halides Enolates are reactive nucleophiles . Although the major enolate Lewis contributor shows concentration of electron density on the electronegative oxygen (Fig. I.1) when it reacts as a nucleophile, it behaves like the electron density is concentrated on the α-carbon next to carbonyl group. However, from the resonance forms shown in Fig. I.1, it is clear that enolates are capable of reacting as both carbon and oxygen nucleophiles ( resonance structures II and I respectively). Enolates react with alkyl halides, aldehydes/ketones and esters and these reactions are shown below:   Reactions of enolates with alkyl halides Enolates are reactive nucleophiles and react with alkyl halides by the S N 2 and E2 mechanism . The electrophiles (alkyl halides in this case) need to be S N 2 reactive...

Keto-Enol Tautomerism – Enolization – Reactions and Mechanism Acid or Base catalyzed Enolization – Reactions and Mechanism Carbonyl compounds (aldehydes, ketones, carboxylic esters, carboxylic amides) react as electrophiles at the sp 2 hybridized carbon atoms and as nucleophiles if they contain an H-atom in the α-position relative to their C=O or C=N bonds. This is because this H is acidic and it can be removed by a base leaving behind an electron pair for nucleophilic attacks .     For most compounds in organic chemistry all the molecules have the same structure – even if this structure cannot satisfactory represented by a Lewis formula – but for many compounds there is a mixture of two or more structurally distinct compounds that are in rapid equilibrium. This phenomenon is called tautomerism . Tautomerism is the phenomenon that occurs in any reaction that simply involves the intramolecular transfer of a proton. An equilibrium is established between the ...