EXPERIMENTAL AND THEORETICAL-STUDY OF SUBSTITUENT EFFECTS ON (3)J((13)C1-H-1) COUPLING-CONSTANTS IN 1-X-BICYCLO[1.1.1]PENTANES

A series of 23 bridgehead-substituted bicyclo[1,1,1]pentanes were synt hesized and the (3)J(C1-H) coupling constants determined from their pr oton-coupled C-13 NMR spectra. It was found that the values of the cou plings are strongly dependent upon the type of substituent present, wi th powerful effects exerted by the halogens in particular. The IPPP-CL OPPA-INDO theoretical approach, which was employed to provide a measur e of the extent of through-bond versus through-space transmission of c oupling information, was found to give (3)J(C1-H) values in good agree ment with experimental data. Empirical substituent parameter regressio ns were performed and found to be consistent with the CLOPPA descripti on of the increase in both the through-bond and through-space contribu tions to the coupling. The substituent parameter regressional analyses also demonstrated that electronegativity effects play a predominant r ole in determining the magnitude of the couplings, particularly in tho se substrates in which the substituent is attached to the ring system by a second-row element.