Q74 / 200 · NEET 2007 · Chemistry

The order of decreasing reactivity towards an electrophilic reagent, for the following would be: (i) benzene (ii) toluene (iii) chlorobenzene (iv) phenol

  • A
    (ii) $>$ (iv) $>$ (i) $>$ (iii)
  • B
    (iv) $>$ (iii) $>$ (ii) $>$ (i)
  • Correct answer
    C
    (iv) $>$ (ii) $>$ (i) $>$ (iii)
  • D
    (i) $>$ (ii) $>$ (iii) $>$ (iv)

Solution

Electrophiles have high affinity for electrons. They attack at the site where electron-density is highest. Electron withdrawing substances increases the electron density. The electron withdrawing tendency decreases in the order : $-\mathrm{OH}>-\mathrm{CH}_3>-\mathrm{H}>-\mathrm{Cl}$ Therefore, the correct order of reactivity towards electrophile is $\mathrm{C}_6 \mathrm{H}_5 \mathrm{OH}>\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_3>\mathrm{C}_6 \mathrm{H}_6>\mathrm{C}_6 \mathrm{H}_5 \mathrm{Cl}$ Related Theory Electrophilic substitution reaction in haloarenes occur slowly because halogen has a negative inductive effect, it decreases the electron density on the benzene ring due to resonance.

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

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