Q78 / 200 · NEET 2010 (Screening) · Chemistry

The correct order of increasing reactivity of $\mathrm{C} \mathrm{X}$ bond towards nucleophile in the following compounds is Figure

  • Correct answer
    A
    I $ < $ II $ < $ IV $ < $ III
  • B
    II $ < $ III $ < $ I $ < $ IV
  • C
    IV $ < $ III $ < $ I $ < $ II
  • D
    III $ < $ II $ < $ I $ < $ IV

Solution

Key Idea Alkyl halides are more reactive towards nucleophilic substitution. Reactivity depends upon the stability of carbocation intermediate formed. Among the given halides, aryl halide $\left(\mathrm{C}_6 \mathrm{H}_5 \mathrm{X}\right)$ is least reactive towards nucleophile as in it the $\mathrm{C}-\mathrm{X}$ bond acquire some double bond character due to resonance. Presence of electron withdrawing groups like $-\mathrm{NO}_2$ at ortho and para positions facilitate the nucleophilic displacenent of $-\mathrm{X}$ of aryl halide. Among alkyl halides, $3^{\circ}$ halides are more reactive as compared to $2^{\circ}$ halides due to the formation of more stable carbocation. Hence, the order of reactivity of $\mathrm{C}-\mathrm{X}$ bond towards nucleophile is as Figure

Hence, the correct answer is option: 'A'.

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