Explain why rate of reaction of Lucas reagent with three classes of alcohols different? Give chemical equations wherever required.

The Lucas reagent is a solution of anhydrous zinc chloride in concentrated hydrochloric acid.

In Tertiary alcohols (3^o) the hydroxyl group is easily substituted by the halide group due to greater stability of the carbocation in comparison to primary carbocation and secondary carbocation formed during the reaction.

The greater stability is due to the more inductively donating alkyl groups. The hyperconjugation effect can also be invoked to explain the relative stabilities of primary, secondary, and tertiary carbocations.

Thus, the correct order of the reaction is 3^o>2^o>1^o alcohols in increasing order.