Nuclear magnetic resonance spectroscopy. Spin-spin coupling of carbon to phosphorus, mercury, nitrogen, and other elements

Spin-spin coupling between carbon and phosphorus, mercury, nitrogen, and boron has been observed in proton-decoupled ^(13)C spectra. One-bond couplings involving carbon are generally positive and two-bond couplings are negative; however, if unhybridized p orbitals are used in the bonding, such as with phosphorus(III) or fluorine, one-bond couplings are negative and two-bond couplings are positive. A comparison of the magnitudes of carbon-phosphorus and carbon-nitrogen couplings with carbon-carbon couplings shows a significant negative contribution to the coupling constants which suggests that average energy approximation should not be used for this kind of comparison. Carbon-mercury couplings correlate well with carbon-carbon or proton-mercury couplings in similar bonding situations.