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Question
Arrange the following compounds in increasing order of rate of reaction towards nucleophilic substitution.
| (a) |  |
| (b) |  |
| (c) |  |
Options
(c) < (b) < (a)
(b) < (c) < (a)
(a) < (c) < (b)
(a) < (b) < (c)
Solution
(a) < (b) < (c)
Explanation:
The presence of an electron-withdrawing group (–NO2) at ortho- and para-positions increases the reactivity of haloarenes. The presence of a nitro group at ortho- and para-positions withdraws the electron density from the benzene ring and thus facilitates the attack of the nucleophile on haloarene. The carbanion thus formed is stabilised through resonance. The negative charge appeared at ortho- and para-positions with respect to the halogen substituent is stabilised by the –NO2 group.
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