Question

$R-OH+HX\to R-X+H_{2}O$. In the given reaction, the reactivity of different alcohols is:

• A. $3^o>2^o>1^o$
• B. $3^o<2^o<1^o$
• C. $3^o<2^o>1^o$
• D. $2^o<1^o>3^o$

Answer 1

The correct option is A $3^o>2^o>1^o$

When treated with HBr or HCl alcohols typically undergo a nucleophilic substitution reaction to generate an alkyl halide and water.

Alcohol relative reactivity order : $3^o>2^o>1^o>\text{methyl}$.

Hydrogen halide reactivity order : $HI>HBr>HCl>HF$ (paralleling acidity order).

The reaction usually proceeds via an $S{N}_1$ mechanism which proceeds via a carbocation intermediate, that can also undergo rearrangement.

Methanol and primary alcohols will proceed via an $S{N}_2$ mechanism since these have highly unfavourable carbocations.

Hence, the correct option is $A$