Optically pure (R)-2-bromo-3,3-dimethylpentane is heated in aqueous ethanol and the substitution proceeds through a free carbocation that undergoes a 1,2-methyl shift to the most stable cation before capture by water. The major alcohol and its optical behaviour are

A3,3-dimethylpentan-2-ol with inverted configuration, (S), optically active
B3,3-dimethylpentan-2-ol, racemic
C2,3-dimethylpentan-3-ol, optically inactive (racemic)
D2,3-dimethylpentan-3-ol as a single enantiomer

Answer: C

Ionisation gives the secondary cation

CH X_{3} - CH X^{+} - C (CH X_{3}) X_{2} - CH X_{2} CH X_{3}

; migration of a methyl group from C-3 to C-2 gives the tertiary cation

(CH X_{3}) X_{2} CH - C X^{+} (CH X_{3}) - CH X_{2} CH X_{3}

. The original stereocentre (C-2) now carries two methyl groups, so it is no longer stereogenic and the planar cation is achiral. Attack by water on either face gives equal amounts of the two enantiomers of 2,3-dimethylpentan-3-ol.

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Optically pure (R)-2-bromo-3,3-dimethylpentane is heated in aqueous ethanol and the substitution proceeds through a free carbocation that undergoes a 1,2-methyl shift to the most stable cation before capture by water. The major alcohol and its optical behaviour are

Answer: C

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