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:
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- tertiary alcohol by \(\mathrm{S_N1}\)
- secondary alcohol by \(\mathrm{S_N2}\)
- tertiary alcohol by \(\mathrm{S_N2}\)
- secondary alcohol by \(\mathrm{S_N1}\)
The Correct Option is A
Solution and Explanation
The alcohol is protonated at \(\mathrm{-OH}\), water leaves to give a carbocation, and \(\mathrm{Cl^-}\) then attacks it (an \(\mathrm{S_N1}\) path).
The rate depends on the stability of the carbocation: \(3^\circ \gt 2^\circ \gt 1^\circ\).
So the tertiary alcohol reacts fastest (turbidity appears immediately), by the \(\mathrm{S_N1}\) mechanism.
Answer: (1) tertiary alcohol by \(\mathrm{S_N1}\)
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