Engineering
Chemistry
Acidic and Basic Strength
Question

Which of the following has maximum pKb value ?

CH3CH2NH2

(CH3CH2)2NH

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Solution

The pKb values of ethanamine, N-methylaniline, N-ethylethaneamine and aniline are 3.29, 9.30, 3.00 and 9.38 respectively.
Thus among the given amines, aniline is the weakest base and has maximum pKb value.
Aliphatic amines ethanamine and N-methylaniline are more basic than aniline because in aniline, the lone pair on nitrogen is in resonance with benzene.
N-methylaniline is more basic than aniline because in N-methylaniline, the methyl group  (an electron releasing group) increases the electron density on nitrogen.

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