State reasons for the following:
i) The pK_b value of aniline is more than that of methylamine.
ii) Ethylamine is soluble in water whereas aniline is not.
iii) Primary amines have higher boiling points than tertiary amines.
i) The pK_b value of aniline is more than that of methylamine.
ii) Ethylamine is soluble in water whereas aniline is not.
iii) Primary amines have higher boiling points than tertiary amines.
Solution
(i) Aniline's lone pair is shared with the ring — weaker base, higher pK (9.38 vs 3.38).
(ii) Ethylamine hydrogen-bonds extensively with water; in aniline the large hydrocarbon ring dominates and resists hydration — insoluble.
(iii) Two N–H bonds let primary amines associate through hydrogen bonds; RN cannot — so 1° > 3° in boiling point.
(ii) Ethylamine hydrogen-bonds extensively with water; in aniline the large hydrocarbon ring dominates and resists hydration — insoluble.
(iii) Two N–H bonds let primary amines associate through hydrogen bonds; RN cannot — so 1° > 3° in boiling point.
CBSE Class 12 Board · 2011 · All India · Subjective