F. Herold et al., Dimers of solid 4-arylhexahydro-1H,3H-pyrido[1,2-c]pyrimidine-1,3-diones. C-13 CP/MAS NMR, x-ray diffraction and semi-empirical MO studies, J PHYS ORG, 13(4), 2000, pp. 213-220
C-13 cross-polarization magic angle spinning NMR data are reported for eigh
t derivatives of 4-aryl-hexahydro-1H,3H-pyrido[1,2-c]pyrimidine-1,3-diones
1-8 and the x-ray diffraction data for 4 with R = 4'-Me. The crystal struct
ure of 4 shows the formation of centrosymmetric dimers via intermolecular h
ydrogen bonds with an N2 ... O11 distance of 2.797(3) Angstrom. Deshielding
of carbonyl carbons in the solids 1-8 as compared with solution shows that
such dimers probably also exist in other compounds. According to the PM3 c
alculations, three types of dimers with two Cl=O ... HN, two C3=O ... HN bo
nds and 'mixed,' i.e. with one Cl=O ... HN and one C3=O ... HN bond, are po
ssible. Copyright (C) 2000 John Wiley & Sons, Ltd.