端基异构体Anomer

α-D-吡喃葡萄糖 [α]D = +112°，β-D-吡喃葡萄糖 +18.7°；任一种溶于水后经开链醛式互变，比旋光度逐渐变为平衡值 +52.7°（约 36% α、64% β）。β 型较多是因为其所有大取代基都处于平伏键。

α-D-Glucopyranose has [α]D = +112° and β +18.7°; either one in water interconverts through the open-chain aldehyde until rotation reaches +52.7° (≈36 % α, 64 % β). β predominates because all its large groups are equatorial.

吡喃糖 C-1 上的电负性取代基（–OR、–X）倾向直立键，超过空间位阻的预期，称端基效应，常用环氧孤对电子 n → σ*(C–X) 超共轭解释。

Electronegative substituents at C-1 of pyranoses prefer the axial position more than sterics predict — the anomeric effect, usually explained by n(O) → σ*(C–X) hyperconjugation.

糖苷键的 α/β 构型决定多糖性质：淀粉、糖原为 α-1,4 连接（人能消化），纤维素为 β-1,4 连接（人不能消化，形成直链纤维）。

Glycosidic α/β configuration defines polysaccharides: starch and glycogen are α-1,4 (digestible by humans), cellulose is β-1,4 (indigestible, forming straight fibres).