定义Definition
饱和化合物中碳原子之间只有单键，每个碳原子都连接了尽可能多的氢或其他原子，如烷烃。不饱和化合物含有碳碳双键或三键，如烯烃、炔烃，能发生加成反应。
In a saturated compound the carbon atoms are joined only by single bonds, each carbon carrying as many hydrogen or other atoms as possible, as in alkanes. An unsaturated compound contains carbon–carbon double or triple bonds, as in alkenes and alkynes, and can undergo addition reactions.
检验不饱和键Testing for unsaturation
加入橙色溴水并振荡：不饱和化合物使其褪色（加成），饱和化合物在暗处不褪色。也可用冷的稀酸性高锰酸钾溶液，不饱和化合物使紫色褪去。
Shake with orange bromine water: an unsaturated compound decolourises it by addition, while a saturated one does not in the dark. Cold, dilute acidified potassium manganate(VII) can also be used; unsaturated compounds remove its purple colour.
不饱和度Degree of unsaturation
不饱和度（缺氢指数）= (2C + 2 + N − H − X) ÷ 2，每个双键或环计 1，三键计 2，苯环计 4。例：C₆H₆ 的不饱和度 = (12 + 2 − 6) ÷ 2 = 4。
The degree of unsaturation (double-bond equivalent) is (2C + 2 + N − H − X) ÷ 2; each double bond or ring counts 1, a triple bond 2 and a benzene ring 4. For C₆H₆: (12 + 2 − 6) ÷ 2 = 4.
饱和与不饱和油脂Saturated and unsaturated fats
动物脂肪多由饱和脂肪酸组成，常温下为固体；植物油含较多不饱和脂肪酸，为液体。植物油经催化加氢可制成人造黄油。
Animal fats are mostly made from saturated fatty acids and are solid at room temperature; vegetable oils contain more unsaturated acids and are liquid. Catalytic hydrogenation of vegetable oils makes margarine.