Attempted prediction of the crystal structures of six monosaccharides

A method is reported to generate possible crystal structures of the six hexopyranoses where comparison with an X-ray determination is possible. In these molecules, internal degrees of freedom are all-important. Using essentially only the information that the space group is P2 1 2 1 2 1 with one molecule in the asymmetric unit, a systematic search was made for all low-energy crystal structures of these substances. The energies were minimized with respect to nine lattice and rigid-body parameters and six intramolecular dihedral angles. The number of possible structures within the range 10 kcal mol −1 is of the order 1000. In all cases, the experimental structure was among them, and in four cases this was either the structure with the lowest energy or only a few tenths of a kcal mol −1 higher. However, in the two other cases the relative energy of the experimental structure was over 5 kcal mol −1 . Such calculations can provide a sensitive test for force fields