Two organophosphorus pesticides: methyl parathion and dicapthon

Structural studies performed in this laboratory of organophosphorus pesticides continue with these related compounds. The -NO2 groups of methyl parathion (systematic name: dimethyl 4-nitrophenyl phosphorothioate, C8H10NO5PS) and dicapthon (systematic name: 2-chloro-4-nitrophenyl dimethyl phosphorothioate, C8H9ClNO5PS) make dihedral angles of 10.67 (8) and 5.8 (1)°, respectively, with the planes of their attached rings, which accompanies angular distortion at the ring C atoms to which the -NO2 groups are attached. Similar distortions are observed at the C atom to which the thiophosphate groups are attached. Significant differences in distances and angles around the phenolic O, versus the -OMe groups, explain why it is the site of hydrolysis for these compounds. A comparison of a torsion angle involving the thiophosphate group and phenolic O atom with similar pesticide structures is given and indicates steric influences on that angle.