(a) (i) There are two -NH2 groups in semicarbazide. However, only one such group is involved in the formation of semicarbazones.

Question

Give a plausible explanation for each one of the following:

(a)

(i) There are two -NH₂ groups in semicarbazide. However, only one such group is involved in the formation of semicarbazones.

(ii) Cyclohexanone forms cyanohydrin in good yield but 2, 4, 6-taimethylcyclohexanone does not

(b) An organic compound with molecular formula C₉H₁₀O forms 2, 4, – DNP derivative, reduces Tollens reagent and undergoes Cannizzaro reaction. On vigorous oxidation it gives 1, 2-benzene dicarboxylic acid. Identify the compound.

Answer 1

(a) (i) Because one of the – NH₂ in semicarbazide is involved in the resonance with group.

(ii) Due to steric hinderance in 2. 4. 6-trimethylcyclohexanone, it doesn’t react with HGN easily.

(b) Compound C₉H₁₀O, forms 2,4- DNP derivative, so it contains a carbonyl group. Also it reduces Tollens reagent therefore carbonyl group is an aldehyde group. Since it undergoes Cannizzaro’s reaction, aldehyde has no α-hydrogen atom, so compound is C₈H₉ CHO. On vigorous oxidation, compound gives 1,2-benzene dicarboxylic acid hence the compound is