Question

The correct order of increasing reactivity of

C-X bond towards nucleophile in the following compounds is:

Options

• I < II < IV < III

• II < III < I < IV

• IV < III > I > II

• III > II < I < IV

Answer 1

I < II < IV < III

Explanation:

The order of reactivity is dependent on the stability of the intermediate carbocation formed by cleavage of C − X bond. The 3° carbocation formed in III will be more stable than its 2° homologue (IV) which in turn will be more stable than arenium ion (I). Moreover, the aryl halide has a double bond character in the C − X bond which makes the cleavage more difficult.

On other hand II will be more reactive than I due to presence of electron withdrawing −NO₂ group. C − X bond becomes weak and undergoes nucleophilic substitution reaction. 

∴ Order: I < II < IV < III.