Theoretical study on the structure of phosphonyl radicals

The experimental a(31P) hyperfine splitting (hfs) constants of the phosphonyl radicals Y2ṖO (Y  Me, OMe, NMe2) are fairly well reproduced by ab initio calculations at the UMP2/DZP/ /TZP level of theory. The large increase observed experimentally in a(31P) with increasing electronegativity of the α-substituents is mainly due to the electronic influence of the α-substituents rather than to an increase in pyramidality at the radical centre as previously suggested. This finding confirms that in localized radicals it is incorrect to obtain structural information simply from the trend of the experimental isotropic hfs constants at the radical centre.