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If p, q and r are the pKb values of methylamine, N-methylamine and N,N-dimethylamine respectively, what is the correct order of p, q and r?

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in Chemistry – Class 12 by (188k points)
If p, q and r are the pKb values of methylamine, N-methylamine and N,N-dimethylamine respectively, what is the correct order of p, q and r?

(a) p > q > r

(b) r > q > p

(c) q > p > r

(d) r > p > q

I got this question in semester exam.

I want to ask this question from Amines Chemical Reactions topic in division Amines of Chemistry – Class 12

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The correct choice is (d) r > p > q

Explanation: This peculiar order of basic strength is due to a combination of inductive, solvation and stearic effects of the alkyl groups in the amines. In methyl substituted amines, the solvation effect superimposes the inductive effect to make CH3NH2 more basic than (CH3)3N. The 2° compound is the most basic because of its higher inductive effect than primary amine and higher solvation than tertiary amine.

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