Examination of the spectra of a series of tolyl-and benzylphosphonium salts, phosphonates, and phosphine oxides shows the existence of two types of long-range 31P-1H spin-spin couplings. Four-bond allylic couplings (1-2.5 Hz) are observed in both series of compounds; the magnitude of 4 J~~ depends upon the position of attachment (sp2 or sp3 carbon) of phosphorus to the allylic triad. Both five-and seven-bond homoallylic couplings are observed in the benzylphosphorus systems. The magnitudes of 'JPH (2.3-2.6 Hz) are greater than those of ?]pH (1 ,1-1,7 Hz). Neither six-bond couplings in the benzyl series nor five-and six-bond couplings in the tolyl analogs are observed. Both inductive hyperconjugation and overlap hyperconjugation coupling mechanisms are considered for the homoallylic interactions; on the basis of certain consistent patterns of JPH behavior and the study of model compounds, the latter mechanism is favored.nvestigations of the proton magnetic resonance spectra

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