Stereoelectronic Effects in the Reactions of Phosphate Diesters. Ab Initio Molecular Orbital Calculations of Reaction Surfaces. 2

Ab initio molecular orbital calculations of the reaction profile for hydroxide-catalyzed hydrolysis of dimethyl phosphate in a number of different conformations reveal large stereoelectronic effects. In the two-step reaction, proceeding via a metastable pentacovalent phosphorane intermediate, both hydroxide attack and methoxidedisplacement steps are stereoelectronicaily controlled. Antiperiplanar lone pairs on the basal ester oxygen in the trigonal bipyramidal transition states facilitate translation of the apical bond. In contrast to previous studies on the stereoelectronic effect, orientation of the leaving bond does not alter the energy of the transition state.