Signs and Mechanisms One-Bond Couplings

The magnetic dipoles of two magnetically active nuclei also may interact directly through space. This interaction, however, is averaged to zero for nuclei in solution by 

The one-bond coupling between carbon-13 and protons is readily measured from the 

The zero intercept of this equation indicates that there is no coupling when the s character is zero, in agreement with the Fermi contact model. 

The one-bond CH coupling ranges from about 100 to 320 Hz, and much of the variation may be interpreted in terms of the 7-s relationship. The coupling constant in cyclopropane (162 Hz) demonstrates that the carbon orbital to hydrogen is approximately sp hybridized. Intermediate values in hydrocarbons may be interpreted in terms of fractional hybridization. The J = 144 Hz for the indicated CH bond in tricyclopentane (4-15) corresponds to 29% s character (sp ), 160 Hz in cubane (4-16) to 32% s character (sp ), and 179 Hz in quadricyclane (4-17) 

Just as the resonance frequency of a nucleus is proportional to its gyromagnetic ratio y, the coupling constant between two nuclei is proportional to the product of both gyromagnetic ratios that is, 7(X-Y) oc 7x7y- Nuclei with very small gyromagnetic ratios, such as 

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