The dependence of 1J(C,H) and 3J(C,H) on a nitrogen lone-pair and carbonyl group.: Application to diazepam

The relatively large difference in the directly bonded (C, H) coupling constants of the C 3) methylene group in diazepam can be attributed to the spatial relationship of the C(3)-H bonds and the C(2)=O group and N(4)- lone pair. INDO - FTP calculated (1)J(C-3, H) values reveal a linear relationship with the C(2)-C(3)-N(4)-C(5) dihedral angle, a non- linear relationship with the C-H bond length and small negative change depending on the N( )-C(2)-C(3)-N(4) dihedral angle. The INDO - FTP calculated (3)J(C-5,H) values depend on the corresponding dihedral angle and the spatial relationships of the C=N double bond and the aryl group.