Ab Initio Structure of O-Methyl Methylphosphonofluoridate

摘要

The molecular structure of 0-methyl methylphosphonofluoridate, (CH3)P((0)(F)(OCH3), has been determined from ab initio SCF calculations. It is the simplest realistic model for all acetylcholinesterase enzyme inhibitors based on methylphosphonofluoridic acid. Structures obtained in STO-3G and 3-21G basis sets are compared. Bond distances and angles agree well with the results of the single experimental study, the primary difference being torsional angles that determine conformation. The computation indicates an eclipsed conformation, the methyl adjacent to the phosphoryl oxygen. It is stabilized by cancellation of intramolecular dipoles. Evidence is presented that the experimental conclusion is incorrect and that an eclipsed conformation should be displayed by other phosphorus esters as well.