Try:
http://www.biochem.ucl.ac.uk/~roman/surfnet/surfnet.html
http://www.sander.embl-heidelberg.de/whatif/chap31.html
Hope it helps,
Jurgen
--
Drs Jurgen F. Doreleijers
NMR spectroscopy, Utrecht University, The Netherlands
mailto:jurgen at nmr.chem.ruu.nl
http://www-nmr.chem.ruu.nl/users/jurgen/jurgen.html