Molecular Structure and Conformation of 4H-l, 3, 2-Benzodioxaphosphorins, Including the Insecticide Salithion

Abstract

The crystal structure of salithion (2-methoxy-4H-1, 3, 2-benzodioxaphosphorin 2-sulfide) was determined by three-dimentional X-ray analysis from diffractometer data. The dioxaphosphorin ring in salithion adopted a distorted half-chair conformation with the P=S bond oriented equatorially in the solid state. The related benzodioxaphosphorins were divided into two classes by the NMR pattern of endocyclic methylene protons. The NMR spectra of the first class, including the cyclic phosphoramidates, phosphonates and phosphonothionates, were shown to be consistent with the presence of one preferred conformer with the axial P=O or P=S bond in solutions. Another class including the phosphates, phosphorothionates, phosphorothiolates and phosphorothiolothionates gave the spectra which suggested an equilibrium of rapidly interconverting conformers.