What happens to the alcohol during the reaction with HBr?

When alcohol reacts with HBr, it undergoes a substitution reaction. In this process, the hydroxyl (-OH) group of the alcohol is replaced by a bromine atom. The HBr provides both the hydrogen proton and the bromide ion. The protonation of the hydroxyl group converts it into a better leaving group, allowing the bromide ion to take its place, resulting in the formation of an alkyl bromide.

In contrast, oxidation would involve the increase in the oxidation state of the alcohol, typically leading to aldehydes or ketones rather than bromides, which is not what occurs in this reaction. Reduction would imply a gain of electrons, often leading to alcohols or alkanes, which again does not represent what is happening with HBr. Dehydration refers to the removal of a water molecule, usually leading to the formation of alkenes from alcohols, which is not relevant when HBr is added since it is focused on substitution rather than the removal of water.

Thus, the alcohol’s reaction with HBr is indeed characterized by this substitution mechanism, leading to the formation of an alkyl bromide.