定义Definition
对映体过量是手性样品中主要对映体比次要对映体多出的摩尔分数，ee = |R − S|/(R + S) × 100%。外消旋体 ee = 0，纯对映体 ee = 100%。
Enantiomeric excess is the mole-fraction excess of the major over the minor enantiomer, ee = |R − S|/(R + S) × 100 % — 0 for a racemate, 100 % for a pure enantiomer.
测定方法Measurement
手性 HPLC/GC/SFC（最常用）；手性位移试剂或手性溶剂化试剂 NMR；与手性试剂衍生化为非对映体后 NMR 或色谱分析（莫舍尔酯）；旋光法（光学纯度，可能有非线性偏差）。
Chiral HPLC/GC/SFC (most common); NMR with chiral shift or solvating agents; derivatisation to diastereomers (Mosher esters) then NMR or chromatography; polarimetry (optical purity, possibly non-linear).
相关量Related quantities
对映体比 er = R:S；ee = (er − 1)/(er + 1)。90% ee 相当于 95:5。IUPAC 近年更推荐报告 er。
Enantiomeric ratio er = R:S; ee = (er − 1)/(er + 1); 90 % ee is 95:5. IUPAC increasingly recommends reporting er.
意义Significance
衡量不对称合成的成功程度；药品质量标准常要求单一对映体药物 ee > 99%。“非线性效应”（卡根）指催化剂 ee 与产物 ee 不成正比。
It measures the success of asymmetric synthesis; single-enantiomer drugs typically require ee > 99 %. Kagan’s ‘non-linear effects’ describe product ee not proportional to catalyst ee.
年表Timeline
- 1971
莫里森与莫舍尔推广 ee 概念
Morrison and Mosher popularise the ee concept
- 1986
卡根报道不对称催化的非线性效应
Kagan reports non-linear effects in asymmetric catalysis