JEE Main · 2013 · 07 Apr 2013 · Offline · General Organic Chemistry

A solution of (-) -1-chloro -1 - phenylethane is toluene racemises slowly in the presence of a small amount of

SbCl_{5}

, due to the formation of :

(A)carbene
(B)carbocation✓ Correct
(C)free radical
(D)carbanion

Answer: (B)

Solution

The Lewis acid

SbCl X_{5}

pulls the chloride off 1-chloro-1-phenylethane, generating a flat, benzylic carbocation. Being planar, that intermediate has lost the handedness of the starting material, and when chloride returns it can add to either face with equal ease, rebuilding both mirror-image forms in equal amount. It is this

S_{N} 1

-type ionisation to a carbocation that slowly racemises the compound.

JEE Main · 2013 · 07 Apr 2013 · Offline · Single correct option

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