Conformations of Trimethyl Phosphite: A Matrix Isolation Infrared and ab Initio Study

Abstract

The conformations of trimethyl phosphite (TMPhite) were studied using matrix isolation infrared spectroscopy. TMPhite was trapped in a nitrogen matrix using an effusive source maintained at two different temperatures (298 and 410 K) and a supersonic jet source. The experimental studies were supported by ab initio computations performed at the B3LYP/6-31++G** level. Computations identified four minima for TMPhite, corresponding to conformers with C(1)(TG(±)G(±)), C(s)(TG(+)G(-)), C(1)(G(±)TT), and C(3)(G(±)G(±)G(±)) structures, given in order of increasing energy. Computations of the transition state structures connecting the C(s)(TG(+)G(-)) and C(1)(G(±)TT) conformers to the global minimum C(1)(TG(±)G(±)) structure were also carried out. The barriers for the interconversion of C(s)(TG(+)G(-)) and C(1)(G(±)TT) to the ground state C(1)(TG(±)G(±)) conformer were 0.2 and 0.6 kcal/mol, respectively. Comparison of conformational preferences of TMPhite with the related carbon compound, trimethoxymethane, and the organic phosphate, trimethyl phosphate, was also made using natural bond orbital analysis.