4 . A
The keto–enol equilibrium lies far to the keto side because the keto form is significantly more
thermodynamically stable than the enol form. This thermodynamic stability stems from the fact
that the oxygen is more electronegative than the carbon, and the keto tautomer puts more
electron density around the oxygen than the enol tautomer. If the enol tautomer is less
thermodynamically stable, it is also higher energy than the keto tautomer.5 . B
The aldol condensation is both a dehydration reaction because a molecule of water is lost, and a
nucleophilic addition reaction because the nucleophilic enolate attacks and bonds to the
carbonyl carbon.
6 . B
This hydrogen is on the carbon between two carbonyls, which means that it is particularly acidic.
This is due to both the inductive effects of the two oxygen atoms in the carbonyls and the
resonance stabilization of the anion between the carbonyl groups.
7 . B
At high temperatures and with a weak base like NH 3 , the thermodynamic enolate will be favored.
The reaction proceeds slowly with the weak base, giving the kinetic enolate time to interconvert
to the more stable thermodynamic enolate.
8 . A
Aldehydes are generally more reactive than ketones because the additional alkyl group of a
ketone is sterically hindering; this alkyl group is also electron-donating, destabilizing the
carbanion intermediate. This eliminates choices (B) and (D). The carbonyl carbon is highly
electrophilic; alkanes lack any significant electrophilicity, eliminating choice (C).