Probability-plot comparison of crystallographically independent molecules

Molecules may be described in terms of chemical coordinates (bond lengths, bond angles and torsion angles) or bonded and non-bonded interatomic distances, as well as by crystallographic coordinates. For studies of molecular geometry, the former is more generally useful. Since random errors in interatomic distances should be normally distributed, they may be used in probability-plot analyses of differences in molecular geometry. Several examples of such analyses are discussed. The method is shown to be applicable to entire molecules or molecular fragments, even when the chemical or crystallographic environment is different. The technique is sensitive to minor changes in conformation which might otherwise be overlooked.