The total number of compounds from below when treated with hot KMnO4, giving benzoic acid is: [figure] , [figure] , [figure] , [figure] , [figure] , [figure] , [figure] , [figure]
- 4
- 3
- 5
- 6
Answer
(3) 5
Solution
Hot alkaline/acidic KMnO4 oxidises a side chain on benzene to –COOH, whatever its length, provided the carbon attached to the ring (benzylic carbon) carries at least one H atom.
Toluene (-CH3), ethylbenzene (-CH2CH3), cumene (-CH(CH3)2), isobutylbenzene (-CH2CH(CH3)2) and propylbenzene (-CH2CH2CH3) all have a benzylic H each gives benzoic acid C6H5COOH: 5 compounds.
tert-Butylbenzene (-C(CH3)3) and 2-phenylpropan-2-ol (-C(OH)(CH3)2) have no benzylic H not oxidised to benzoic acid.
4,4′-Dimethylbiphenyl gives biphenyl-4,4′-dicarboxylic acid, not benzoic acid.
Number of compounds = 5
Answer: (3)