Hindered rotation around a C-*PH bond: a single-crystal EPR study of the diphenyldibenzobarrelenephosphinyl radical

Research was conducted to examine the barrier to rotation of the P-H group around the C-*P bond using a new phosphine, the diphenyldibenzobarrelenephosphine. The EPR spectrum of the resulting phosphinyl radical, trapped in a single crystal of diphenyldibenzobarrelenephosphine, was examined at 77 K and at room temperature after homolytic scission of a P-H bond by radiolysis. Results indicate that interaction between the phosphinyl hydrogen and the phenyl ring bound to the ethylenic bond explains the potential energy profile.