C-H center dot center dot center dot O and C-H center dot center dot center dot N hydrogen bond networks in the crystal structures of some 1,2-dihydro-N-aryl-4,6-dimethylpyrimidin-2-ones

A set of three aryl dimethyl pyrimidinones have been studied and their crys tal structures described in terms of networks of C-H ... O and C-H ... N hy drogen bonds. Two of the three molecules in this study differ in the replac ement of a chloro group by a methyl group and obey the chloro-methyl exchan ge rule in that they have nearly identical crystal structures. However, and in contrast to other pairs of compounds so related, the chloro and methyl groups here are not merely isosteric but also form similar polarization-ind uced Cl ... Ph and CH3... Ph contacts. These conjugated molecules may offer some scope for nonlinear optical studies. (C) 2000 Academic Press.