(a) Give a possible explaination for each one of the following : -
(i) There are two - `NH_(2)` groups in semicarbazide. However, only one such group is involvedin the formation of semicarbazones.
(ii) Cyclohexanone forms cyanohydrin in good yield but `2,4,6`-trimethylcyclohexanone does not.
(b) An organic compound with molecular formula`C_(9)H_(10)O` forms, `2,4`- DNP derivative, reduces Tollens' reagent and undergoes Cannizzaro reaction.
On vigorous oxidation it gives 1,2-benzene-di-carboxylic acid. Identify the compound.

Explanation

(i) In semicarbazieds, out of two `-NH_(2)` groups, one of the `NH_(2)` group bounded to
`-overset(O)overset(||)(C )-` is involved in conjugation through its lone pair.

Electron deusity on -`NH_(2)` group involved in resonance also decrease. Hence it cannot act as nucleophite. Hence other `NH_(2)` act as nucleophile.

Due to steric hindrane posed by three methyl group and around carbonyl group `2,4,6`- Trimethyl cylohexanone, it will not give yield of cyanohydrin.
(i) As `C_(9)H_(10)O` reduces tollen's reagent, it is an aldehyde or ketone.
(ii) As `C_(9)H_(10)O` reduces Tollen's reagent, it is an aldehyde .
(iii) As `C_(9)H_(10)O` undergoes cannizaro's reaction, it is substituted benzaldehyde.
(iv) As `C_(9)H_(10)O` gives `1,2` Benzene-di-carboxylic acid, the compound is
.