An unknown alcohol is treated with the "Lucas reagent" to determine whether the alcohol is primary, secondary or tertiary. Which alcohol reacts fastest and by what mechanism?

Question

An unknown alcohol is treated with the "Lucas reagent" to determine whether the alcohol is primary, secondary or tertiary. Which alcohol reacts fastest and by what mechanism?, Tertiary alcohol by $ S_{N} 2 $, Secondary alcohol by $ \mathrm{S}_{\mathrm{N}} 1 $, Tertiary alcohol by $ S_{N} 1 $, Secondary alcohol by $ \mathrm{S}_{\mathrm{N}} 2 $

MARKS App · Accepted Answer

Lucas reagent is a mixture of conc. HCl and dry anhydrous ZnCl 2 . In this reaction, a carbocation is formed as an intermediate and thus the stability and ease of carbocation formation determine the rate of the reaction as that's the slow step of the mechanism. Hence, the order of reactivity is tertiary alcohol > secondary alcohol by S N 1 mechanism. Thus, with Lucas reagent, tertiary alcohol reacts fastest and by S N 1 mechanism.

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