DIPOLAR-CHEMICAL SHIFT NMR-SPECTRA OF THE CARBON NITROGEN LINKAGE IN BENZYLIDENEANILINE - CARBON AND NITROGEN CHEMICAL SHIELDING ANISOTROPIES

The magnitudes and orientations of the principal components of the carbon and nitrogen chemical shift tensors for the "localized" imine moiety of the Schiff base benzylideneaniline have been determined by the analysis of dipolar-chemical shift NMR spectra. The carbon chemical shift anisotropy was determined to be 156 ±2 ppm with η = 0.88 ±0.02 whereas the nitrogen shift anisotropy was found to be 545 ±2 ppm with η = 0.92 ±0.01. The most shielded component of both the carbon and nitrogen shift tensors is approximately perpendicular to the imine fragment. For the imine carbon the intermediate component of the shift tensor is approximately along the C=N axis. The corresponding component of the nitrogen chemical shift tensor is oriented along the direction of the nitrogen lone pair. These results are compared to those available in the literature for related molecules. For the 13C, 14N spin pair, the 13C dipolar-chemical shift NMR spectrum cannot be accurately simulated if the high-field approximation for the 14N nucleus is assumed. To circumvent this problem, a general equation is described that can be used to calculate the dipolar-chemical shift NMR spectrum of a spin 1/2 nucleus dipole coupled to a spin 1 nucleus where the high-field approximation is not invoked. © 1990 American Chemical Society.