A comparison of semi-empirical and AB initio methods on the hydrolysis of phosphinates, phosphonates, and phosphates

The hydrolysis of phosphorus fluoridates was studied by semiempirical and a b initio methods. The reaction proceeds through a metastable intermediate s eparated from the reactants and products by transition structures, Both met hods gave similar qualitative results; however, the first transition (forma tion of the trigonal bipyrimid intermediate) occurred earlier and the secon d (loss of F-) later with semiempirical methods. Including solvation in the calculations is critical. The AMSOL program generated reasonable energies especially when the limitations of the semiempirical Hamiltonian are consid ered, The Onsanger model was not a significant improvement over calculation s on isolated molecules.