JEE Main · 2014 · 06 Apr 2014 · Offline · Compounds Containing Nitrogen

Considering the basic strength of amines in aqueous solution, which one has the smallest pKb value?

(A)(CH₃)₃N
(B)C₆H₅NH₂
(C)(CH₃)₂NH✓ Correct
(D)CH₃NH₂

Answer: (C)

Solution

The smallest

p K_{b}

marks the strongest base. In water the order is

(CH X_{3}) X_{2} NH > CH X_{3} NH X_{2} > (CH X_{3}) X_{3} N > C X_{6} H X_{5} NH X_{2}

: the secondary amine strikes the best balance between the electron-donating methyls and solvation of its protonated form, trimethylamine is held back by crowding that hampers that solvation, and aniline is weakest because its nitrogen lone pair is pulled into the ring. So

(CH X_{3}) X_{2} NH

has the smallest

p K_{b}

JEE Main · 2014 · 06 Apr 2014 · Offline · Single correct option

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