Abstract
The symmetry groups of nonrigid molecules first defined by Longuet–Higgins, in the most general cases are generalized wreath product groups. We first outline the representation theory of wreath product groups. Then the representation theory of generalized wreath product groups is developed. Several illustrative examples of NMR groups are offered. The character tables of several nonrigid molecular groups are presented. An example of a nonrigid triphenyl molecule is given to illustrate the use of the generalized wreath product in deriving optical selection rules.