JEE Main · 2020 · 03 Sep 2020 · Shift 2 · Haloalkanes and Haloarenes

The decreasing order or reactivity of the following compounds towards nucleophilic substitution

(S_{N} 2)

is:

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

Answer: (B)

Solution

The rate of an

S_{N} 2

reaction rises as the carbon bearing the leaving group is made more electrophilic by electron-withdrawing groups acting through induction and resonance. The para-dinitro compound (III) places both nitro groups where their

- I

and

- M

effects tell fully, making it the most reactive. The ortho-dinitro compound (II) keeps strong inductive withdrawal though its resonance is hindered by crowding, placing it next. The meta-dinitro compound (IV) offers only moderate inductive help and no resonance, and the compound with no withdrawing groups (I) is least reactive. The decreasing order is (III) > (II) > (IV) > (I).

JEE Main · 2020 · 03 Sep 2020 · Shift 2 · Single correct option

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JEE Main · 2020 · 03 Sep 2020 · Shift 2 · Haloalkanes and Haloarenes

Solution

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