High level ab initio quantum mechanical model chemistries have been used to
study the relative stabilities of the simple phosphine oxides tautomers OP
H3/PH2OH and OPH(OH)(2)/P(OH)(3) and related molecules. It is found that th
e two PH,OH isomers are virtually equi-energetic and only slightly move sta
ble than OPH3 itself; and the oxides with one or move hydroxyl groups ave s
ignificantly move stable than their hydroxide tautomers. The difference in
stability arises mainly from the variation of the P=O bond energy among the
various species, the P=O bond energy increasing with the number ofhydroxyl
groups present. The effects of solvation in aqueous solution ave estimated
by reaction field polarized continuum models and by explicit calculations
of OPH3 and PH2OH hydrogen bound to a single water molecule. Both approache
s indicate that the oxide form is significantly stabilized by its aqueous e
nvironment. (C) 2000 John Wiley & Sons, Inc.