Introduction: We have seen that the carbonyl group of aldehydes and ketones is highly immediate, and that accompaniments to this functionality are ordinary. Carbonyl functionality reactive but that it also activates to hand carbon-hydrogen bonds (particularly alpha hydrogen’s) to go through a variety of substitution reactions.1
Carbonyl compounds can be explained by just four fundamental reaction types:
Nucleophilic additions
Nucleophilic acyl substitutions
α-Substitutions
Carbonyl condensations2 α-Substitutions: Alpha-substitution reactions take place at the site next to the carbonyl group the α-position and occupy the substitution of an α hydrogen atom by an electrophile, E,
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Unimolecular - rate depends on concentration of only the substrate.
Does NOT occur with primary alkyl halides (leaving groups).
Strong acid can promote loss of OH as H2O or OR as HOR if tertiary or conjugated carbocation can be synthesized.15
Comparison of Enolization and Nucleophilic Reactions
Enolization Nucleophilic Reactions
1) In this type of reaction tautomerism happens. 1) In these types of reactions there is no phenomenon of tautomerism is happens.
2) They are also known as alpha substitution reactions. 2) They are may be known as substitution or elimination reactions.
3) An enol is formed in these type of reactions 3) No enol is formed in these reactions.
4) It is only applicable to those compounds which contain alpha hydrogen. 4) There is no limitation of alpha hydrogen.
5) Usually the carbonyl containing compounds are being studied in these types of reactions. 5) Usually the alkyl halides are being studied in these types of reactions.
6) The enolate ion that is formed is a conjugate base. 6) The nucleophile may be strong or weak base
7) The activity of enolate depends on PH. 7) The activity of nucleophile depends on the alkyl