Conformation of dioxopiperazines

2,5‐Dioxopiperazines (DOPs), due to their conformational variability, provide a unique type of six‐membered ring, for which the general ring‐puckering formalism may be fully explored. First, it is shown, through the analysis of 65 X‐ray DOP structures, that any experimental conformation of the DOP ring (e.g. one described in terms of its six endocyclic torsion angles) is perfectly described by the formalism, with an average precision being not worse than 0.2° for any torsion angle type. Next, some applications of the treatment are visualized. They include: (i) A very simple test for an immediate check if originally reported values of endocyclic torsion angles are mutually consistent; (ii) Some generalizations concerning conformational dynamics of the DOP ring; (iii) Implications for solution studies and for the investigations of other types of six‐membered rings.