Aldehydes and Ketones II: Enolates (7)

alpha-carbon

the carbon adjacent to the carbonyl carbon

alpha-hydrogens

the hydrogens attached to the alpha-carbon

Acidic; Strong

alpha-hydrogens are relatively ________ and can be removed by a _______ base

Weakens

the electron-withdrawing oxygen of the carbonyl __________ the C—H bonds on alpha-carbons

Enolate

results from deprotonation and can be stabilized by resonance with the carbonyl

Ketones

are less reactive toward nucleophiles because of steric hindrance and alpha-carbanion destabilization

Alkyl Group

the presence of an additional this crowds the transition step and increases its energy

Less

the alkyl group donates electron density to the carbanion, making it _______ stable

Keto Form

C = O; the traditional form of aldehydes and ketones

Enol Form

ene + ol = double bond + hydroxyl group; less common form of aldehydes and ketones

Tautomers

are isomers that can be interconverted by moving a hydrogen and a double bond. The keto and enol forms are these of each other

Enolate

the enol form can be deprotonated to form this. These are good nucleophiles

Michael Addition

an enolate attacks an alpha, beta-unsaturated carbonyl, creating a bond

Kinetic Enolate

is favored by fast, irreversible reactions at lower temperatures with strong, sterically hindered bases

Thermodynamic Enolate

is favored by slower, reversible reactions at higher temperatures with weaker, smaller bases

Enamines

are tautomens of imines. Like enols, these are the less common tautomer

Aldol Condensation

the aldehyde or ketone acts as both nucleophile and electrophile, resulting in the formation of a carbon-carbon bond in a new molecule called an aldol

Aldol

contains both aldehyde and alcohol functional groups

Nucleophile

is the enolate formed from the deprotonation of the alpha-carbon

Electrophile

is the aldehyde or ketone in the form of the keto tautomer

Condensation Reaction

occurs in which the two molecules come together

Dehydration Reaction

after the aldol is formed, this occurs. It is a loss of a water molecule. This results in an alpha, beta- unsaturated carbonyl

Retro-aldol Reactions

are the reverse of aldol condensation. These are catalyzed by heat and base. In these reactions, the bond between an alpha- and beta-carbon is cleaved