Space groups rare for organic structures. III. Symmorphism and inherent molecular symmetry

Abstract

To a close approximation, the relative frequency of the space groups of molecular organic compounds is determined by ease of packing. When the molecules are in general Wyckoff positions, the relative frequency anticorrelates with the degree of symmorphism. Somewhat different considerations apply if the molecule possesses and uses some inherent symmetry (\overline 1, 2, m, 2/m, 222, mm, ...) [Kitaigorodskii (1955); Kitaigorodskii (1961). Organic Chemical Crystallography. New York: Consultants Bureau]. The observed frequencies are analysed in the light of the degree of symmorphism and molecular symmetry.