Theoretical Rotation, Pseudorotation and Pseudoinversion Barriers for the Hydroxyphosphoranyl Radical

Cramer, C. J.
J. Am. Chem. Soc. 1990, 112, 7965.

Hydroxyphosphoranyl, H₃POH^*, has been studied computationally and found to have two local minimum equilibrium structures. Each is characterized by a trigonal bipyramidal geometry in which the unpaired electron is localized equatorially. They differ in the disposition of the hydroxyl group, either axial (preferred) or equatorial. All possible transition states for the permutation of any number of substituents have been located and characterized at the MP2/6-31G*//6-31G* + ZPVE level. Pseudorotation intermediates were found to have trigonal bipyramidal geometries in which the unpaired electron is localized axially. Pseudorotations permuting only hydrogen atoms had barriers of 4-10 kcal/mole. Interconversion of the two local minima for H₃POH^* was found to be accomplished more efficiently by a pseudoinversion process (14.9 kcal/mol) than a pseudorotation (17.0 kcal/mol). Analysis of the distribution of spin density in H₃POH^* is provided and arguments about the controversial geometries of two other phosphoranyl radicals are analyzed therewith.