Exo-exo and endo-endo vicinal proton spin-spin coupling constants in norbornane and norbornene. An IPPP-CLOPPA analysis

CAVASOTTO, CLAUDIO N.; GIRIBET, CLAUDIA G.; RUIZ DE AZÚA, MARTIN C.; CONTRERAS, RUBEN H.

JOURNAL OF COMPUTATIONAL CHEMISTRY

JOHN WILEY & SONS INC

Año: 1991 vol. 12 p. 141 - 146

0192-8651

The IPPP-CLOPPA method is used to study the origin of the difference between exo-exo and endo-endo vicinal interproton couplings in norbornane and norbornene. The main pathway defining such couplings is found to be determined by the corresponding CH bonds and antibonds. For this reason they can be considered to be transmitted through space. Contributions from excitations involving MOs of bridge 7 and the CH endo and exo bonds and antibonds are found to be negligible in both compounds. Even though bridges 5–6 and 7 are not included in the coupling pathway, they influence the structure of endo and exo CH bonds, and thus cause the nonequivalence of endo-endo and exo-exo couplings. Results obtained with the NNBI method are compared to those of IPPP-CLOPPA.