L. 7 Enols & Aldols

Question 1

Identify the Alpha Carbon and Hydrogen in a

Ketone and Aldehyde molecule

Answer 1

Ketone ( Two R Carbonyl Groups)

Aldehyde (One Carbonyl group & one Hydrogen)

Question 2

Alpha-Hydrogens

(Properties)

Answer 2

• The electron-withdrawing oxygen of the carbonyl weakens the C-H
• bond the alpha-carbon.
• The ENOLATE resulting from deprotonation be stabilized by resonance with the carbonyl.

Question 3

Keytones vs Aldehydes

(Reactivity)

Answer 3

Keytones are less reactive towards nucleophiles because of

• steric hindrance coming from the extra R group (alkyl groups in intermediate increase energy)
• alpha-carbanion destabilization (alkyl group donates electron density to carbanion = less stabilized)

Question 4

KETO-ENOL Tautomerization

Answer 4

Aldehydes and Ketones exist in the traditional

Keto form (C=O) and in the less common

Enol form (ene +ol = double bond + Hydroxyl group)

• Tautomers are Constitutional Isomers that can be interconverted by moving a hydrogen and a double bond.
• Enol can be deprotonated to form an ENOLATES. Good nucleophiles.

Question 5

Michael Addition

Answer 5

Enolate attacks an alpha-beta unsaturated carbonyl

creating a bond between both molecules

Question 6

Kinetic vs Thermodynamic Enolates

Answer 6

Kinetic;

fast, irreversible, low T, strong and sterically hindered base. Less stable.

Thermodynamic;

Slow reversible, high T, weaker smaller bases.

(Attacks more substituted carbon)

Question 7

Enamines

Answer 7

Enamine —-> Imine

Are tautomers of imines, like enols, enamines are the less common tautomer

Question 8

Aldol Condensation Reaction

Answer 8

• Nucleophilic Addition to carbonyl
• Aldehyde or Ketone both as electrophile or nucleophile
• Electrophile = Keto &. Nucleophile = Enol
• Forming carbon-carbon bond = New molecule = ALDOL
• ALDOL = Alcohol + Aldehyde
• Enolate is nucleophile
• 1st = Condensation Reaction
• 2nd = Dehydration reaction, resulting in cleaved bond between an alpha,beta-carbon.

Question 9

Retro-Aldol reaction

Answer 9

The reverse of aldol condensation

• Aq base and heat
• breaking bonds between alpha and beta carbons
• stabilized intermediate enolate (hydration)

Question 10

Aldehyde & Ketone VS other functional groups

(reaction)

Answer 10

No leaving groups as compared to all other functional groups