. Account for the following


Account for the following

(i) pKb of methylamine is less than that of aniline.

(ii) Aniline does not undergo Friedel–Crafts reaction.

(iii) Ethylamine is freely soluble in water whereas aniline is only slightly soluble.

Best Answer

(i) In aniline, due to resonance, the lone pair of electrons on the nitrogen atom are delocalized over the benzene ring. As a result, the electron density on the nitrogen decreases. On the other hand, in methyl amine +ve I effect of CH3 increases the electrondensity on the nitrogen atom. Therefore aniline is a weaker base than methyl amine and hence its pKb value is higher than that of methyl amine

(ii) Aniline being a Lewis base reacts with lewis acid AlCl3 to form a salt. Due to this, N atom of aniline acquires positive charge and hence acts as a strong deactivation group for further reaction

(iii) Ethyl amine is freely soluble in water because it forms hydrogen bonds with water molecules

 hydrocarbon

On the other hand in aniline due to large, hydrocarbon part, the extent of hydrogen bonding decreases considerably and hence aniline is slightly soluble

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