CHEM 0320 Lecture Notes - Lecture 1: Enol, Nucleophilic Substitution, Alpha And Beta Carbon
Document Summary
Strong bases can remove an alpha hydrogen resulting in enolate ions or enolates. In the enolate ion, the inductive effect of the positively polarized carbonyl carbon strongly stabilizes the negative chare at the alpha position. Deprotonation of an unsymmetric ketone may lead to two isomeric species, a more substituted and a less substituted enolate. The more substituted double bond is more stable than the less substituted. When there is an absence of a proton source and low temperatures, equilibrium with the more stable enolate does not occur and the kinetic enolate can be used as such (less hindered more easily removed) At room temperature and in the presence of a proton source equilibrium of the kinetic with the more stable thermodynamic enolate takes place it occurs by reversible proton exchange between unreacted ketone and the respective regioisomeric enolates. An alternative way to access thermodynamic enolates is the use of hydroxide in water or alkoxides in alcohols as bases.
