Correlation between C-H and C-C spin-spin coupling constants and s character of hybrids calculated by the maximum overlap method

For some thirty hydrocarbons the s character of hybrids obtained by the application of the maximum overlap method have been correlated with C-H and C-C spin-spin coupling constants. The following relationships were obtained: $$J_{{text{C}}^{{text{13}}} - {text{H}}} = 1079a_{{text{CH}}}^{text{2}} /(1 + S_{{text{CH}}}^{text{2}} ) - 54.9$$ , $$J_{{text{C}}_{text{1}}^{{text{13}}} - {text{C}}_{text{2}}^{{text{13}}} } = 1020.5a_{{text{C}}_{text{1}} }^2 a_{{text{C}}_{text{2}} }^{text{2}} /(1 + S_{{text{CC}}}^{text{2}} ) - 8.2$$ . Here the coupling constants are expressed in cps units. In the calculation of the maximum overlap hybrids either the experimental bond lengths or a standard bond lengths were used. For the (J_{{text{C}}^{{text{13}}} - {text{H}}}) and (J_{{text{C}}^{{text{13}}} - {text{H}}} ) coupling constants the standard deviations are 0.9 cps and 1.9 cps respectively. It has been suggested that the large additive constant in the (J_{{text{C}}^{{text{13}}} - {text{H}}}) correlation may be attributed to the ionic character of C-H bonds. A good agreement with the experimental data strongly supports the idea that the Fermi contact term and the hybridization are dominant factors in determining carbon-hydrogen and carbon-carbon spin-spin coupling constants across one bond, at least in hydrocarbons.