Ch. 7: Aldehydes and Ketones II: Enolates

Question 1

Alpha carbon

Answer 1

The carbon adjacent to the carbonyl carbon. The electron withdrawing oxygen of the carbonyl weakens the C-H bonds on alpha carbons.

Question 2

Alpha Hydrogens

Answer 2

Hydrogens attached to the alpha carbon. Alpha hydrogens are relatively acidic and can be removed by a strong base. The electron withdrawing oxygen of the carbonyl weakens the C-H bonds on alpha carbons. The enolate resulting from deprotonation can be stabilized by resonance w the carbonyl

Question 3

Ketones

Answer 3

Less reactive toward nucleophiles bc of steric hindrance and alpha carbanion destabilization. The presence of an additional alkyl group crowds the transition step and increases its energy. The alkyl group also donates electron density to the carbanion, making it less stable

Question 4

Forms in which aldehydes and ketones exist in are…

Answer 4

Traditionally keto form (C=O)and in less commonly enol form (ene + ol = double bond + hydroxyl group)

Question 5

Tautomers

Answer 5

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

Question 6

Enolate

Answer 6

The enol form can be deprotonated to form an enolate. Good nucleophiles.

Question 7

Michael Addition

Answer 7

An enolate attacks an alpha, beta-unsatured carbonyl, creating a bond

Question 8

Kinetic enolate

Answer 8

Favored by fast, irreversible reactions at lower temperatures w strong, sterically hindered base

Question 9

Thermodynamic enolate

Answer 9

Favored by slower, reversible rxns at higher temps w weaker, smaller bases

Question 10

Enamines

Answer 10

Tautomers of imines. Like enoles, enamines are the less common tautomer

Question 11

Aldol condensation

Answer 11

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. The nucleophile is the enolate formed from the deprotonation of the alpha carbon. The electrophiles is the aldehyde or ketone in the form of the keto tautomer. First a condensation rxn occurs in which 2 molecules come together. After the aldol is formed a dehydration rxn (loss of a water molecule) occurs. This results in an alpha, beta unsaturated carbonyl

Question 12

Aldol

Answer 12

Contains both aldehyde and alcohol functional groups.

Question 13

Retro-aldol reactions

Answer 13

Reverse of aldol condensations–catalyzed by heat and base. The bond between an alpha and beta carbon is cleaved