Nuclear Magnetic Resonance Spectroscopy. ^(13)C-^(15)N Coupling Constants as a Conformational Probe?

There have been several attempts to explain the variation in ^(13)C-^(l5)N coupling constants with the stereochemical orientation of the carbons with respect to the nitrogen lone pairs. Most of the substances investigated so far, however, have the possibility of averaging of coupling constants due to bond rotation and/or nitrogen inversion. The only relatively rigid substances looked at have had aromatic nitrogen, and, with these, other effects are expected to play a role