Test: Physical Properties & General Reaction (February 11) - NEET MCQ

(i) It has a carbonyl carbon that turns chiral on reduction with hydrides. Hence, with LiAIH₄ or aluminium isopropoxide, gives racemic mixture. Also, it has no other functional groups, either Clemmensen reduction or Wolff-Kishner reduction can be used.
(ii) It has an olefinic double bond, Clemmensen reduction would not be suitable for selective reduction of carbonyl group.
(iii) LiAlH₄ also reduces primary halide but aluminium isopropoxide does not. Wolff-Kishner reduction would not be suitable because HO^- reacts with halide group (E_N2 or E2).
(iv) Same reasons as with (i).

NaBH₄ brings about reduction of carbonyls by hydrid e transfer mechanism at planar sp² carbon. Hence, if a chiral carbon is generated, racemic mixture is always produced.

In MPV reduction, carbonyl is reduced to alcohol while isopropoxide fraction of reducing agent is oxidised to acetone.

With aluminium isopropoxide (MPV reduction), carbonyls are selectively reduced to alcohols leaving other groups intact.

One pair of enantiomers for each (I) and (II) while two pairs of enantiomers for (III). 

Clemmensen reduction is suitable for reductio n of carbonyls containing additional acidic functional group.

IV is enantiomeric. Its pure enantiomer, with HCN/NaCN, would produce pair of diastereomers.

H^- (hydride) ion undergoes nu cle ophilic ad dition at sp² carbon of carbonyls. Aldehydes are more reactive than ketones due to less steric hindrance in former case. Since, nucleophilic attack of hydride ion occur at planar carbonyl carbon, there is equal probability of attack from both side of plane giving racemic mixture if chiral carbon is generated.