High resolution 13C nuclear magnetic resonance spectra for symmetrical orthodihalobenzenes including long-range 13CH couplings
Analysis of high resolution 13C NMR spectra for symmetrical orthodihalobenzenes have provided all long-range 13CH coupling values in orthodichloro-, dibromo-, and diiodobenzene. Furthermore, since the analyses were sensitive to the sign of the coupling constants, the relative signs of these long-range 13CH couplings have been determined from unique spectral fits. The substituent effects on the chemical shifts in this series of compounds appear to be additive. The 13CH couplings are compared with coupling values in other compounds and are shown to be related to substituent electronegativity. The absolute magnitude of the 13CH couplings for these halogen-substituted compounds are larger than those observed in benzene, with but one exception. In all cases, three-bonded 13CH couplings are found to be larger than the two-bond values.