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Question: The compound(s), which gives benzoic acid on oxidation with $KMnO_4$, is (are) : ...

The compound(s), which gives benzoic acid on oxidation with KMnO4KMnO_4, is (are) :

A

Only (I), (II) and (III)

B

Only (II) and (IV)

C

Only (II) and (III)

D

Only (I), (II) and (IV)

Answer

Only (II) and (IV)

Explanation

Solution

Under KMnO4KMnO_4 oxidation, an alkylbenzene is converted to benzoic acid only if the alkyl substituent possesses at least one benzylic hydrogen (a hydrogen on the carbon directly attached to the benzene ring).

  • (I) Tert-butylbenzene: The tert-butyl group, –C(CH₃)₃, has no benzylic hydrogen. No oxidation.
  • (II) Isobutylbenzene: The benzylic carbon has one hydrogen. Oxidizes to benzoic acid.
  • (III) Biphenyl: No alkyl side chain is present; the two rings are directly bonded, so there is no suitable benzylic hydrogen. No oxidation.
  • (IV) Sec-butylbenzene: The sec-butyl group has a benzylic hydrogen. Oxidizes to benzoic acid.

Thus, the compounds that yield benzoic acid on oxidation with KMnO4KMnO_4 are (II) and (IV).