MCAT Organic Chemistry - Aldehydes and Ketones II: Enolates

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α-carbon

adjacent to the carbonyl carbon

α-hydrogens

hydrogens connected to the α-carbon, very acidic and easily deprotonated, leaving negative charge

ketones < aldehydes (steric hinderance)

carbanion

molecule with a negatively charged carbon atom

enol

presence of a carbon–carbon double bond (the en– component) and an alcohol (the –ol component)

tautomers

isomers which differ in the placement of a proton and the double bond

enolization/tautomerization

interconverting from the keto to the enol tautomer

equilibrium: ketone < < < enol

α-racemization

any aldehyde or ketone with a chiral α-carbon will rapidly become a racemic mixture as the keto and enol forms interconvert

Michael addition

the carbanion attacks an α,β-unsaturated carbonyl compound, a molecule with a multiple bond between the α- and β-carbons next to a carbonyl

kinetic product

formed more rapidly but is less stable; double bond to the less substituted α-carbon; formed by the removal of the α-hydrogen from the less substituted α-carbon because it offers less steric hindrance

thermodynamic product

formed more slowly, but is more stable and features the double bond being formed with the more substituted α-carbon; formed by the removal of the α-hydrogen from the more substituted α-carbon

Enamines

tautomers of imines; interconvertible

aldol condensation

nucleophilic addition to a carbonyl; aldehyde or ketone acts both as an velectrophile (in its keto form) and a nucleophile (in its enolate form); end result is the formation of a carbon–carbon bond

aldol

a molecule that contains both aldehyde and alcohol functional groups

Dehydration of aldol

E1 or E2 mechanism

retro-aldol reaction

reverse of aldol condensation; aqueous base is added and heat is applied