In: Chemistry
23. KCN is insoluble in benzene but in the presence of 18-crown-6 the nucleophilic substitution reactions take place very fast using CNas nucleophile- Justify with mechanism.
24. Arylamines and heterocyclic aromatic amines are considerably less basic than alkylamines — Justify.
25. p-Anisidine is more basic than aniline — Justify with appropriate drawings.
23. Benzene is non polar whereas KCN is polar that is ionic in nature. So in nonpolar solvent like benzene it is remain insoluble.
But in presence of 18-crown-6 solvent, the K+ ion of KCN is strongly chelated by six oxygen atom of 18-crown-6. As a result the -CN ion become totally free so called naked and then soluble in benzene and undergo very faster nucleophilic attack.
24. The lone pair of amine(-NH2) group of arylamines and heterocyclic aromatic amines are conjugated to the aromatic ring due to +R-effect. Therefore, the lone pair is not only available for the attack towards a new acid. That means aromatic amines are less basic.
Whereas, aliphatic amines have opposite effect that is electron pushing effect (+I-effect) of alkyl group and hence the lone pair the nitrogen atom of amine group is only available to the acid. That is why aliphatic amines are more basic than aromatic amines.