(a) Give a possible explanation for each one of the following:
(i) There are two $- N H_{2}$ , 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-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's reaction. On vigorous oxidation it gives 1, 2-benzene-di-carboxylic acid. Identify the compound?

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Solution

(a) (i) Semicarbazide undergoes resonance involving only one of the two-NH 2 groups, which is attached directly to the carbonyl carbon atom.
Therefore, the electron density on $- N H_{2}$ group involved in the resonance also decreases.
As a result, it cannot act as a nucleophile. Since the other $- N H_{2}$ group is not involved in resonance, it can act as a nucleophile and can attack carbonyl carbon atoms of aldehydes and ketones to produce semicarbazones.
(ii) Cyclohexanone form cyanohydrins according to the following equation.
In this case, the nucleophile $C N^{-}$ can attack without any steric hindrance. However, in the case of 2, 4, 6-trimethylcyclohexanone, methyl groups at $\in \pm$ -position offer steric hindrances and as a result, $C N^{-}$ cannot attack effectively.
For this reason, it does not form a cyanohydrin.
(b) It is given that the compound (with molecular formula $C_{9} H_{10} O$ forms 2, 4-DNP derivative and reduces and Tollen's reagent. Therefore, the given compound must be an aldehyde.
Again, the compound undergoes Cannizzaro reaction and on oxidation gives 1, 2-benzenedicarboxylic acid. Therefore, the $- C H O$ group is directly attached to a benzene ring and this benzaldehyde is ortho-substituted. Hence, the compound is 2-ethylbenzaldehyde
The given reaction can be explained by the following equations.

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Q. An organic compound with the 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 dicarboxylic acid. Identify the compound.

Give plausible explanation for each of the following:

(i) Cyclohexanone forms cyanohydrin in good yield but 2, 2, 6 trimethylcyclohexanone does not.

(ii) There are two −NH₂ groups in semicarbazide. However, only one is involved in the formation of semicarbazones.

(iii) During the preparation of esters from a carboxylic acid and an alcohol in the presence of an acid catalyst, the water or the ester should be removed as soon as it is formed.

An organic compound with the molecular formula C₉H₁₀O forms 2, 4-DNP derivative, reduces Tollens’ reagent and undergoes Cannizzaro reaction. On vigorous oxidation, it gives 1, 2-benzenedicarboxylic acid. Identify the compound.

Q. Consider the following statements
(i) Out of two

- N H_{2}

groups in semicarbazide only one is involved in formation of semicarbazones.
(ii) Cyclohexane froms cyanohydrin in good yield but

2, 2, 6 - t r i m e t h y l c y c l o h e x a n o n e

does not.
(iii) The

α - h y d r o g e n s

in aldehydes and ketones are acidic.

Q. An organic compound with molecular formula

C_{9} H_{10} O

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