Q18 of 116 Page 377

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.

Only one Amino group is involved in the resonance structure of semicarbazide hence e- density on NH2 group decreases & it can’t act as a nucleophile. But another NH2 group can attack as a nucleophile to form semicarbazones.


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17

Complete each synthesis by giving missing starting material, reagent or products

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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:

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.

 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.