Question

(i) Arrange the following set of compounds in the order of their decreasing relative reactivity with an electrophile. Give reason.

(ii) Give one important structural difference between cyclohexanol and phenol.

Answer 1

(i) The methoxy group (-OCH₃) is electron releasing group. It increases the electron density in benzene nucleus due to resonance effect (+R-effect). Hence, it makes anisole more reactive than benzene towards the electrophile. In case of alkyl halides, the electron density increases at ortho and para positions due to +R effect.

However, the halogen atom also withdraws electrons from the ring because of its -I effect. Since the -I effect is stronger than the +R effect, the halogens are moderately deactivating. Thus, overall electron density on benzene ring decreases, which makes further substitution difficult. -NO₂ group is electron withdrawing group. It decreases the electron density in benzene nucleus due to its strong -R-effect and strong -I-effect. Hence, it makes nitrobenzene less

Therefore, overall reactivity of these three compounds towards electrophiles decreases in the following order:

Anisole > Chlorobenzene >Nitrobenzene

(ii) In phenol, benzene ring has alternate single and double bonds while cyclohexanol is alicyclic compound.

Cyclohexanol

Phenol