Q18 of 116 Page 377

Give plausible explanation for each of the following:

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.

It is the reversible reaction hence if we don’t remove the water or ester the reaction may proceed in backward direction, for that It is essential the water or ester as soon as formed.


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18

Give plausible explanation for each of the following:

Cyclohexanone forms cyanohydrin in good yield but 2,2,6-trimethylcyclohexanone does not.

 18

Give plausible explanation for each of the following:

There are two –NH2 groups in semicarbazide. However, only one is involved in the formation of semicarbazones.

 19

An organic compound contains 69.77% carbon, 11.63% hydrogen and rest oxygen.

The molecular mass of the compound is 86. It does not reduce Tollens’ reagent but forms an addition compound with sodium hydrogensulphite and give positive iodoform test. On vigorous oxidation it gives ethanoic and propanoic acid. Write the possible structure of the compound.

 20

Although phenoxide ion has more number of resonating structures than carboxylate ion, the carboxylic acid is a stronger acid than phenol. Why?