Relative Signs of the 31P-1H and 31P-C-1H Nuclear Magnetic Resonance Coupling Constants

The possibility that terms other than Fermi contact interaction make significant contributions to nuclear spin-spin coupling with heavy nuclei has stimulated considerable interest in the n.m.r. spectra of compounds containing heteroatoms. In particular, relative signs and magnitudes of J_(XCH) and J_(XCCH) have be en reported for ethyl derivatives of several heavy isotopes of spin 1/2. In order to understand better the factors responsible for spin coupling with a representative heavy nucleus, we have analyzed the spectra of (CH_3)_3P, (CH_3)_2PH, and (CH_3)PH_2 and have obtained relative signs and magnitudes of J_(PH) and J_(PCH).