RECONSIDERATION OF THE STEREOELECTRONIC EFFECT IN OXYPHOSPHORANE SPECIES

Properties of various oxyphosphoranes such as neutral pentahydroxyphos phorane (doubly protonated 3b) and dianionic trihydroxyphosphorane (3b ) and trimethoxyphosphorane (3a) were examined by ab initio molecular orbital calculations. The energies of the stationary points were evalu ated at the MP2 level of theory with the 6-31+G basis. The analysis o f the oxyphosphorane species indicates that the orientation of the equ atorial methoxyl group determines the mode of formation/cleavage of th e axial P-O-2/P-O-5 bond. This dependence of the reactivity on the con formation of the equatorial P-O-3 bond is in accord with the predictio n that is based on the stereoelectronic effect. However, the present w ork shows that the long-postulated ''n-sigma orbital interaction'' is not predominant in the stereoelectronic control of the oxyphosphorane system.