Structure of a five-membered ring containing a phosphinyl radical: ab initio predictions and single-crystal EPR study

The geometry of the five-membered ring (1) containing a phosphinyl radical is studied by ab initio molecular orbital calculations. X-irradiation of a single crystal of 1,3-benzazaphosphole (2) generates the cyclic phosphinyl radical (3) whose EPR parameters are obtained and compared with those calculated for 1. Experimental and calculated results show that, in 3, the five-membered ring adopts a distorted "envelope" structure and that a rapid inversion motion occurs at room temperature