Question

An unknown alcohol is treated with the "Lucas Reagent" to determine whether the alcohol is $1^{\circ },2^{\circ }$ or $3^{\circ }$. Which alcohol reacts the fastest and by what mechanism?

• A. Secondary alcohol by $S_{N}1$
• B. Tertiary alcohol by $S_{N}1$
• C. Secondary alcohol by $S_{N}2$
• D. Tertiary alcohol by $S_{N}2$

Answer 1

The correct option is B Tertiary alcohol by $S_{N}1$

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