Dihedral angle

A dihedral angle is the angle between two intersecting planes. In chemistry it is the angle between planes through two sets of three atoms, having two atoms in common. In solid geometry it is defined as the union of a line and two half-planes that have this line as a common edge. In higher dimension, a dihedral angle represents the angle between two hyperplanes.

Definitions

A dihedral angle is an angle between two intersecting planes on a third plane perpendicular to the line of intersection.

A torsion angle is a particular example of a dihedral angle, used in stereochemistry to define the geometric relation of two parts of a molecule joined by a chemical bond.

Dihedral angles in stereochemistry

In stereochemistry every set of three (not co-linear) atoms of a molecule defines a plane. When two such planes intersect, the angle between them is a dihedral angle. Dihedral angles are used to specify the molecular conformation. Stereochemical arrangements corresponding to angles between 0° and ±90° are called syn (s), those corresponding to angles between ±90° and 180° anti (a). Similarly, arrangements corresponding to angles between 30° and 150° or between -30° and -150° are called clinal (c) and those between 0° and ±30° or ±150° and 180° are called periplanar (p).