MNDO-PM3 study on gas-phase alkaline hydrolysis of phosphoryl and thiophosphoryl fluorides

Abstract

The gas-phase alkaline hydrolysis of phosphoryl and thiophosphoryl fluorides was theoretically examined by using the semiempirical MNDO-PM3 molecular orbital method. The potential-surface analysis showed that the facial attack of the hydroxide ion from the backside toward one of the P–F bonds was thermodynamically favored. The three trigonal bipyramidal and one square pyramidal pentacoordinate species were specified as stable intermediates by a reaction coordinate method. The vibrational analysis of transition states demonstrated that these permutational isomers were interconverted by Berry's pseudorotation process. The larger activation enthalpy of permutation was required for most pentacoordinate species from thiophosphoryl fluoride through permutation than phosphoryl fluoride. The apical departure of the fluoride ion from the pentacoordinate species was enegetically most favorable.