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

The gas-phase alkaline hydrolysis of phosphoryl acid thiophosphoryl fluorid es was theoretically examined by using the semiempirical MNDO-PM3 molecular orbital method. The potential-surface analysis showed that the facial atta ck of the hydroxide ion from the backside toward one of the P-F bonds was t hermodynamically favored. The three trigonal bipyramidal and one square pyr amidal pentacoordinate species were specified as stable intermediates by a reaction coordinate method. The vibrational analysis of transition states d emonstrated 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 thro ugh permutation than phosphoryl fluoride. The apical departure of the fluor ide ion from the pentacoordinate species was enegetically most favorable. ( C) 2001 Elsevier Science B.V. All rights reserved.