Structural effects on the chemical shift of exo - endo and exo - exo tetra cyclo dodecane

The systematic investigation of rigid cyclic molecules has provided a basis for a number of concepts presently employed in NMR spectroscopy. Bicyclic systems of norbornyl family have been extensively studied in this respect but their tetracyclic analogs have received much less attention. The large number of peaks that into narrow chemical shift ranges and the presence of intramolecular affects that arise from groups brought into close proximity have probably been responsible for this state of affairs. As in the case of other polycyclic rings of interest, more data from model systems would be desirable. We have analysed the proton and carbon-13 spectra of endo-endo tetra cyclo [6.1.13,6.02,7] dodeca-4-en-10-ol (1A) and its analogs and found interactions between atoms that are four or more bonds away. Although these upfield δ and δE effects could be accounted for by invoking steric interactions similar to those that give to the well-know γgauche effect, there are other discrepancies between carbon-13 chemical shifts of tetracyclic dodecanes and their bicyclic analogs that are not amenable to simple rationalizations and a look other situations where such effects may be present would be recommendable. (author)