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 - NH_3, 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

Give plausible explanation for each of the following (i) Cyclohexanone

1.	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 - NH_3, 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
Answer» Solution :(i) Nucleophilic attack by the `CN^(-)` ion does not occur in reaction II due to steric hindrance. There is no such steric hindrance in cyclohexanone, therefore, nucleophilic attack by the `CN^-` ion occurs readily and hence cyclohexanone cyanohydrin is obtained in good yield. (ii) Lone pair of electrons on the -NH, group ATTACHED directly to carbonyl group is involved in resonance as SHOWN above. As a result, electron density on this NH group decreases and hence it does not act as a nucleophile. However, the lone pair of electrons on the other NH group (ie, attached to NH) is not involved in resonance and hence is available for nucleophilic attack on the C =0 group. (III) The formation of esters from a carboxylic acid and an alcohol in presence of an acid catalyst is a reversible reaction. `underset("Carboxylic acid")(RCOOH) + underset("Alcohol")(ROH) overset(H_(2)SO_(4)) To shift the EQUILIBRIUM in the forward direction, the water or the ester formed should be removed as fast as it is formed.