An unknown alcohol is treated with the "Lucas reagent" to determine whether the alcohol is primary…

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 SN2
  2. Tertiary alcohol by SN2
  3. Secondary alcohol by SN1
  4. Tertiary alcohol by SN1

Solution

3° alcohol reacts fastest giving white turbidity immediately on adding Lucas reagent.
Reaction takes place through carbocation formation involving SN1 mechanism. Rate of reaction in this reaction is directly proportional to the stability of the carbocation formed.
3° R-OH(tertiary alcohol) forms 3° carbocation and therefore, the reaction is fastest.

Asked in: JEE Main 2013 (07 Apr)

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