The structures of pyrimidines and purines. I. A determination of the structures of 2-amino-4-methyl-6-chloropyrimidine and 2-amino-4,6-dichloropyrimidine by X-ray methods

The structures of two isomorphous pyrimidines 2-amino-4-methyl-6-chloropyrimidine and 2-amino-4,6-dichloropyrimidine have been studied by X-ray methods. The molecules are based on planar six-membered rings with the C-C and C-N bonds in the ring having approximately 50% double-bond character. It is found that for the compound containing the methyl group, the methyl groups and the chlorine atoms are distributed at random throughout the structure in two chemically, but not crystallographically, equivalent positions in the molecules. The structure is held together by the van der Waals forces between the chlorine atoms of adjacent molecules and by a system of hydrogen bonds.