Alcohols and Ethers - Result Question 10

####13. 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?

(a) Secondary alcohol by $S _N 1$

(2013 Main)

(b) Tertiary alcohol by $S _N 1$

(c) Secondary alcohol by $S _N 2$

(d) Tertiary alcohol by $S _N 2$

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Answer:

Correct Answer: 13. (b)

Solution:

  1. The reaction of alcohol with Lucas reagent is mostly an $S _N 1$ reaction and the rate of reaction is directly proportional to the stability of carbocation formed in the reaction. Since $3^{\circ}$ $R$ - $OH$ forms $3^{\circ}$ carbocation (most stable), hence it will react fastest.


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