The hydroxyl group is the –OH functional group characteristic of alcohols, consisting of an oxygen atom bonded to a hydrogen atom and to a carbon. It matters because the polar O–H bond lets alcohols form hydrogen bonds with one another, which is why they are relatively high-boiling and often water-soluble. The hydroxyl group should not be confused with the hydroxide ion (OH⁻): hydroxyl is a covalently bound group, whereas hydroxide is a free anion.

羟基是醇的特征官能团 –OH,由一个氧原子连接一个氢原子和一个碳原子构成。它之所以重要,是因为极性的 O–H 键使醇分子之间能形成氢键,这正是醇沸点相对较高且常可溶于水的原因。羟基不应与氢氧根离子(OH⁻)相混淆:羟基是共价结合的基团,而氢氧根是游离的阴离子。