比旋光度Specific rotation

l 以 dm、c 以 g/mL（纯液体用密度）代入；严格单位为 deg·mL·g⁻¹·dm⁻¹，习惯只写度数。报告时注明温度、波长（D 线 589 nm）、溶剂和浓度，如 [α]²⁰_D = +66.5（c 1.0，H₂O）。

Use l in dm and c in g/mL (density for neat liquids); the unit deg mL g⁻¹ dm⁻¹ is usually omitted. Report temperature, wavelength (D line, 589 nm), solvent and concentration, e.g. [α]²⁰_D = +66.5 (c 1.0, H₂O).

鉴定手性化合物、测定光学纯度（ee ≈ [α]观测/[α]纯）、监测蔗糖转化（右旋蔗糖水解为左旋的“转化糖”）和糖的变旋现象。

Identifying chiral compounds, estimating optical purity (ee ≈ [α]obs/[α]pure), following sucrose inversion (dextrorotatory sucrose → laevorotatory invert sugar) and sugar mutarotation.

比旋光度的正负与 R/S 构型无对应关系；不同溶剂、pH 下符号甚至可反转（如乳酸）。少量高旋光杂质会严重影响结果，现代 ee 测定多用手性色谱。

The sign does not map onto R/S, and can even reverse with solvent or pH (lactic acid). Small amounts of highly rotating impurities distort results; modern ee measurements use chiral chromatography.