Gaussian 03
Spin-Spin Coupling
Determining Conformations via Spin-Spin Coupling Constants
Conformational analysis is a difficult problem when studying new compounds for which X-ray structures are not available. Magnetic shielding data in NMR spectra provides information about the connectivity between the various atoms within a molecule. Spin-spin coupling constants can aid in identifying specific conformations of molecules because they depend on the torsion angles with the molecular structure.
Gaussian 03 can predict spin-spin coupling constants in addition to the NMR shielding and chemical shifts available previously. Computing these constants for different conformations and then comparing predicted and observed spectra makes it possible to identify the specific conformations that were observed. In addition, the assignment of observed peaks to specific atoms is greatly facilitated.