Reaction of Alcohols with HX - Dehydrohalogenation

Dehydrohalogenation only takes place with secondary and tertiary alcohols. The reaction begins with protonation in acidic conditions of a hydroxyl group. The hydroxyl group is converted into a leaving group and it departs as water. The carbocation intermediate formed attracts a nucleophile, in this case a halide ion, completing the SN1 substitution. This reaction competes with acid-catalyzed dehydration (E1 elimination).