The stereochemical dependence of 13C nuclear magnetic resonance chemical shifts and 13C–31P couplings in some dialkylphosphonocyclohexanes

Abstract

13C chemical shifts and 13C–31P couplings are reported for 15 dialkylphosphonocyclohexanes. Data are compared to those for three related hydroxyphosphonates. Both direct and vicinal 13C–31P couplings are useful stereochemical probes. Materials with equatorial phosphorus exhibit one bond couplings larger by ca. 5 Hz than their axial counterparts. Vicinal couplings follow an approximate dihedral angle dependence but are attenuated by OH substitution. In addition to the expected gauche-γ shielding effects, pentavalent phosphorus substituents induce minor (ca. 1 ppm) upfield shifts at carbons to which they bear an anti-periplanar relation.