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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?

1. secondary alcohol by S_N2
2. tertiary alcohol by S_N2
3. secondary alcohol by S_N1
4. tertiary alcohol by S_N1

Correct answer: tertiary alcohol by S_N1

Solution

Tertiary alcohols react fastest with Lucas reagent because they undergo the S_N1 mechanism, which involves the formation of a stable carbocation. The tertiary carbocation is more stable than secondary or primary ones, allowing for a quicker reaction.

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