I'm looking for the best and most recent parametrization of the Karplus
equation for vicinal (3 bond) J(CH) coupling constants, particularly in
situations where one or more of the three carbons involved in the pathway
are sp2 rather than sp3 hybridized. In particular, one J value of interest
is H-C-C-C=O where the C=O is an a,b unsaturated ketone (unsat. is not in
the pathway). We have a minimized structure (natural product) which
predicts a dihedral of ~30 degrees, but the J value is very small (~1.8
Hz). It seems that a lot of work has been done recently on these couplings
in 13C-labelled proteins so there should be a growing body of data
available, for example, on H(beta)-C-C(alpha)-C=O couplings.
Neil
Neil E. Jacobsen, Ph.D.
NMR Facility Manager
Department of Chemistry
University of Arizona
Tucson, AZ 85721
520-621-8146
FAX 520-621-8407