Interdependence of phosphorus-31-selenium-77 NMR coupling constants in bicyclic phosphorus selenide compounds

Bicyclic compounds exo,exo-alpha -P4Se3X2 and exo,exo-alpha -P4Se3XI (X = C N, NMePh or NPr2i) and endo,exo-alpha -P4Se3(CN)(2) have been made in solut ion and their P-31 and Se-77 NMR spectra completely analysed. Ab initio cal culations of P-31 and Se-77 NMR shieldings in exo,exo- and endo,exo-alpha - P4Se3(CN)(2) and in exo,exo-alpha -P4Se3(CN)I confirmed these assignments. In an unsymmetric compound exo,exo-alpha -P4Se3XI the twelve P-31-Se-77 NMR coupling constants have values related to those in the corresponding symme tric compounds exo,exo-alpha -P4Se3X2 and exo,exo-alpha -P4Se3I2 by simple rules, useful for predicting couplings in exo,exo-alpha -P4Se3X2 when the s pectra of exo,exo-alpha -P4Se3XI and exo,exo-alpha -P4Se3I2 have already be en analysed.