What type of reaction occurs when alcohol reacts with HBr?

When an alcohol reacts with HBr, a substitution reaction takes place. In this process, the hydroxyl group (-OH) of the alcohol is replaced by a bromine atom (Br). This is characteristic of nucleophilic substitution reactions, where a nucleophile (Br in this case) displaces a leaving group (the hydroxyl group).

Alcohols contain a polar -OH bond, making the oxygen atom slightly negative and the hydrogen atom slightly positive. When HBr is added, the hydrogen ion (H+) from HBr interacts with the hydroxyl group, converting it into a better leaving group. Subsequently, the Br− ion, which is a stronger nucleophile, attacks the carbon atom that was bonded to the -OH group, resulting in the formation of an alkyl bromide.

This reaction showcases the nucleophilic substitution mechanism (specifically, an S(_N)1 or S(_N)2 mechanism depending on the structure of the alcohol), affirming that the correct description of the reaction type is a substitution reaction. Therefore, it’s clear why this classification fits the process being described.