The increasing order of the $\mathrm{pK}_{\mathrm{b}}$ of the following compound is :

(A) (c) $<$ (a) $<$ (d) $<$ (b)

(B) (b) $<$ (d) $<$ (a) $<$ (c)

(C) (a) $<$ (c) $<$ (d) $<$ (b)

(D) (b) $<$ (d) $<$ (c) $<$ (a)

JEE Main · 2019 · 12 Apr 2019 · Shift 1 · Compounds Containing Nitrogen

The increasing order of the

pK_{b}

of the following compound is :

Answer: (A)

Basicity and

p K_{b}

run opposite ways: the more basic the compound, the smaller its

p K_{b}

. Electron-donating groups push charge toward the basic centre and raise basicity (lower

p K_{b}

), while electron-withdrawing groups do the reverse. Here the substituents rank as (c)

NO X_{2}

strongly withdrawing, (a)

F

weakly withdrawing, (d)

CH X_{3}

weakly donating and (b)

OCH X_{3}

strongly donating. In order of increasing

p K_{b}

this is (c)

<

(a)

<

(d)

<

(b).

JEE Main · 2019 · 12 Apr 2019 · Shift 1 · Single correct option