定义Definition
纽曼投影式沿某一 C–C 键轴方向观察分子：前面的碳用点（三条键交于圆心）表示，后面的碳用圆圈（键从圆周伸出）表示，便于看出构象和二面角。
A Newman projection views a molecule along a C–C bond: the front carbon is a point where three bonds meet, the rear carbon a circle with bonds from its edge, showing conformations and dihedral angles clearly.
用途Uses
比较重叠式与交叉式、邻位交叉（gauche，60°）与对位交叉（anti，180°）构象的能量；分析 E2 消除所需的反式共平面、卡普拉斯方程中的二面角、费尔金–安模型中亲核试剂进攻方向。
Comparing eclipsed and staggered, gauche (60°) and anti (180°) conformations; analysing the anti-periplanar geometry of E2, dihedral angles for the Karplus equation and nucleophile trajectories in the Felkin–Anh model.
由来Origin
美国化学家梅尔文·纽曼于 1952 年提出。
Introduced by the American chemist Melvin Newman in 1952.
示例Example
丁烷 C2–C3 键：对位交叉最稳定，邻位交叉高约 3.8 kJ/mol，全重叠（两甲基重叠）最高约 19 kJ/mol。
Butane C2–C3: anti is most stable, gauche about 3.8 kJ/mol higher, and the fully eclipsed (methyls eclipsed) about 19 kJ/mol higher.
年表Timeline
- 1952
纽曼提出投影式
Newman introduces the projection