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Question

Give reasons for the following:
(i) Aniline does not undergo Friedal- Crafts reaction.
(ii) (CH3)2NH is more basic than (CH3)3N in an aqueous solution.
(iii) Primary amines have higher boiling point than tertiary amines.

Solution
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(i) Aniline does not undergo Friedel craft's reactions because the reagent AlCl3 (the Lewis acid which is used as a catalyst in friedel crafts reaction), being electron deficient acts as a Lewis base. and attacks on the lone pair of nitrogen present in aniline to form an insoluble complex which precipitates out and the reaction does not proceed.

(ii) With increase in alkyl group, the +I effect will increase which will increase the ease of donation of lone pair electron. But in water one other factor is controlling the strength of basicity. Amine will accept a proton and form cation. This cation will be stabilised in water by salvation. Better the salvation by hydrogen bonding, higher will be the basic strength.(refer image)

Thus with increase in methyl group, hydrogen bonding and stabilisation by salvation decreases. The net effect is when we move from secondary to tertiary amine basic strength

(iii) In a tertiary amine there aren't any hydrogen atoms attached directly to the nitrogen. That means that hydrogen bonding between tertiary amine molecules is impossible. That's why the boiling point is much lower. The small amines of all types are very soluble in water.


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Similar Questions
Q1
Give reasons for the following:
(i) Aniline does not undergo Friedal- Crafts reaction.
(ii) (CH3)2NH is more basic than (CH3)3N in an aqueous solution.
(iii) Primary amines have higher boiling point than tertiary amines.
View Solution
Q2
Account for the following:

(i) Primary amines (RNH2) have higher boiling point than tertiary amines (R3N).

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

(iii) (CH3)2NH is more basic than (CH3)3N in an aqueous solution.

View Solution
Q3
Amines are classified as primary, secondary and tertiary amine.
(a) Represent the structure of secondary and tertiary amine.
(b) How will you convert nitrobenzene to aniline?
(c) Aniline does not undergo Friedel-Crafts reaction. Why?
View Solution
Q4
Give reasons (CH3)2NH is more basic than (CH3)3N in an aqueous solution.
View Solution
Q5

Give plausible explanation for each of the following:

(i) Why are amines less acidic than alcohols of comparable molecular masses?

(ii) Why do primary amines have higher boiling point than tertiary amines?

(iii) Why are aliphatic amines stronger bases than aromatic amines?

View Solution