JEE Advanced · 2014 · 25 May 2014 · Paper 1 · Alcohols Phenols and Ethers

Molecular weight 100 corresponds to ${\mathrm{C}}_6{\mathrm{H}}_{12}\mathrm{O}$ (ketones). When a ketone is reduced by ${\mathrm{NaBH}}_4$, it forms a secondary alcohol. A racemic mixture is produced when the reduction creates a new chiral center at the carbonyl carbon.

For a racemic product:
• The carbonyl carbon must become chiral after reduction (i.e., the two groups attached to it must be different).
• The ketone itself may be achiral or chiral (if chiral, each stereoisomer is counted separately).

Systematic analysis of ${\mathrm{C}}_6{\mathrm{H}}_{12}\mathrm{O}$ ketones:

1. Pentan-2-one derivatives with branching that create chirality upon reduction.
2. Hexan-3-one and its branched isomers.
3. Ketones with existing chiral centers that create a new chiral center upon reduction.

Counting all such ketones (including stereoisomers counted separately as stated): 5 ketones give racemic products.

Answer: 5