Protonation of an alcohol is the addition of a hydrogen ion (H⁺) to the oxygen of the hydroxyl group. It matters because it turns the poor leaving group –OH into the good leaving group –OH₂⁺, which can then depart as a neutral water molecule. This step is essential for substitution and elimination of alcohols, since the bare hydroxide ion is too poor a leaving group to leave on its own under most conditions.

醇的质子化是把一个氢离子(H⁺)加到羟基的氧原子上。它之所以重要,是因为它把不良离去基团 –OH 转化为良好的离去基团 –OH₂⁺,后者随后能以中性水分子的形式离去。这一步对醇的取代和消除至关重要,因为裸露的氢氧根离子在大多数条件下都太差,无法自行离去。