13C-13C Coupling Constants in Bridgehead Polycycloalkanecarboxylic Acids

Article abstract of DOI:10.1021/jo00238a021

A series of bicyclic and polycyclic systems substituted with the 13C-labeled carboxyl group at the bridgehead have been synthesized for 13C NMR analysis.It is found that one-bond coupling to the bridgehead carbon atoms shows a reasonable correlation with s character.Vicinal coupling to the unsubstituted bridgehead carbon in the bicyclic compounds was observed to be considerably smaller than anticipated.Calculated values of ³J(13C-13C_bridgehead) obtained by SCF MO calculations performed at the INDO level are in excellent agreement with those determined experimentally and demonstrate that the magnitude of ³J(C-C) is a reflection of opposing through-bond and through-space contributions.On the basis of the MO calculations, the large four-bond 13C-1H coupling in bicyclo<1.1.1>pentane-1-carboxylic-6-13C acid can be attributed almost entirely to the effect of through-space interactions.