ABSTRACT: This report presents the energy details
related to mechanistic pathways of tautomeric
interconversion between phosphinous acids and
phosphine oxides with different substituents using
DFT, MP2 and CCSD (T) calculations. Four mechanisms
consisting of simple, dimer, water-assisted
(with 1, 2, and 3 molecules of water), and methanol-
assisted have been considered. In the most
cases and all pathways, the halogen-containing
phosphorus compounds preferred phosphinous acid
tautomer and the other structures preferred phosphine
oxide tautomers. In simple tautomerism, the
high-energy barriers showed the impossible pathway
for this interconversion and halogen substituents
had higher rate constants. In dimeric
mechanism, the relative stability of phosphine
oxide tautomer was increased and the tautomeric
processes via this mechanism were found to have
the higher rates versus the simple mechanism. In
the solvent-assisted mechanism, except one structure,
the relative stability of phosphinous acids
was increased in comparison with the simple or
dimer cases. Moreover, activation energies showed
the great enhancements in the rates of these interconversions
in the direct presence of the solvent.
© 2016 Wiley Periodicals, Inc. Heteroatom Chem.