ABSTRACT
Many biologically active molecules such as sugars and proteins are chiral (see Section 9.1.2). If all the chiral molecules in a crystal have the same handedness, then the point groups associated with the crystal can only have proper operations. e proper operations for the crystallographic point groups are found in point groups 1, 2, 3, 4, and 6. A proper point group is a point group that has only proper operations. Proper point groups are also called pure rotational point groups (Burns and Glazer, 2013, p. 71). Biochemists who deal mainly with chiral molecules oen use the term “chiral point groups” (Rupp, 2010, p. 227) for the proper point groups. e term “proper point group” is used in this book because molecules or formula units that are not chiral-that is, that do not have a handednesscan form in the proper point groups. An example is α-cristobalite with point group 222 (see Chapter 12).
