JEE Main · 2020 · 06 Sep 2020 · Shift 1 · Compounds Containing Nitrogen

The increasing order of

pK_{b}

values of the following compounds is:

I (see structure)
II (see structure)
III (see structure)
IV (see structure)

(A)II $<$ IV $<$ III $<$ I
(B)I $<$ II $<$ IV $<$ III✓ Correct
(C)II $<$ I $<$ III $<$ IV
(D)I $<$ II $<$ III $<$ IV

Answer: (B)

Solution

Basicity of these anilines is governed by how available the nitrogen lone pair is, and a lower

p K_{b}

marks a stronger base. The para-methoxy compound has its lone pair reinforced by the

+ R

effect of

- OCH X_{3}

, making it the strongest base with the smallest

p K_{b}

. The meta-cyano compound is weakened by the

- I

and

- R

pull of

- CN

, the meta-hydroxy compound lies between them, and the ortho-hydroxy compound ties up its lone pair in intramolecular hydrogen bonding, making it the weakest base with the largest

p K_{b}

. The increasing order of

p K_{b}

is thus para-methoxyaniline

<

meta-cyanoaniline

<

meta-hydroxyaniline

<

ortho-hydroxyaniline.

JEE Main · 2020 · 06 Sep 2020 · Shift 1 · Single correct option

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JEE Main · 2020 · 06 Sep 2020 · Shift 1 · Compounds Containing Nitrogen

Solution

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