Identify the Alpha Carbon and Hydrogen in a
Ketone and Aldehyde molecule
Ketone ( Two R Carbonyl Groups)
Aldehyde (One Carbonyl group & one Hydrogen)
- 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.
Keytones vs Aldehydes
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)
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.
Enolate attacks an alpha-beta unsaturated carbonyl
creating a bond between both molecules
Kinetic vs Thermodynamic Enolates
fast, irreversible, low T, strong and sterically hindered base. Less stable.
Slow reversible, high T, weaker smaller bases.
(Attacks more substituted carbon)
Enamine ----> Imine
Are tautomers of imines, like enols, enamines are the less common tautomer
Aldol Condensation Reaction
- 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.
The reverse of aldol condensation
- Aq base and heat
- breaking bonds between alpha and beta carbons
- stabilized intermediate enolate (hydration)
Aldehyde & Ketone VS other functional groups
No leaving groups as compared to all other functional groups