The electronic effect of lone pairs on the nuclear spin coupling constants

Abstract

There has recently been considerable interest in the electronic effect of lone pairs on the nuclear spin coupling constants (1-6). The lone pair electrons on the nitrogen or oxygen atoms have been accepted to affect the geminal protonproton spin coupling constants in adjacent CH2 fragments (4, 7). The large positive coupling constants for geminal protons in formaldehyde and imines have been interpreted as the result of delocalization of an electron from adjacent lone pair orbital to the antisymmetric CH, orbital (7). Recently it has also been reported that there are striking effects of the nitrogen lone pairs orientation on the 14N-C-H and 15N-C-H coupling constants for H&=iS-R fragments in imines (I) and oximes (II) (4-6). Q ui e recently we reported that the t directly bonded 13C-H coupling constant also depends upon the orientation of the nitrogen lone pair electrons in oxime (II) and aziridine (III) (8).