torsionangle

The torsion angle, also known as a dihedral angle, is a fundamental concept in chemistry and molecular modeling used to describe the three-dimensional arrangement of atoms in a molecule. It quantifies the rotation around a central chemical bond. Imagine four atoms connected in a chain, A-B-C-D. The torsion angle is defined by the angle between the plane containing atoms A, B, and C and the plane containing atoms B, C, and D.

Specifically, the torsion angle is measured between the bond A-B and the bond C-D, with the axis of rotation being the bond B-C. Conventionally, positive torsion angles represent a counterclockwise rotation when viewed from the perspective of atom B looking towards atom C, while negative angles represent a clockwise rotation. The range of possible torsion angles is from 0 to 360 degrees, or equivalently, from -180 to +180 degrees.

The conformation of a molecule, which refers to its spatial arrangement, is significantly influenced by its torsion angles. Different torsion angles can lead to distinct molecular shapes, such as eclipsed or staggered conformations around a bond. These conformational differences can have profound effects on a molecule's physical and chemical properties, including its reactivity, stability, and biological activity. In fields like protein folding, the torsion angles of the polypeptide backbone are crucial for determining the protein's final three-dimensional structure. Computational chemistry extensively uses torsion angles to explore potential energy surfaces and predict molecular geometries.