Elucidating the Gas Phase Thermochemistry and the H‑Atom Abstraction Reactions of Triethyl Phosphite.

Triethyl phosphite (TEPI), an organophosphorus compound, offers potential applications in flame-retardant materials, organic synthesis, homogeneous catalysis, agrochemicals, and pharmaceutical intermediate production. However, TEPI has received little attention compared to more extensively studied phosphates and phosphonates, with its thermal decomposition and chemical reactivity, particularly under combustion and high-temperature conditions, remaining largely unexplored. This study addresses that gap by analyzing the thermochemical properties and reaction kinetics of TEPI to clarify its combustion behavior and support the accurate modeling of its reaction pathways. In this study, the M06-2X/6-311++G-(d,p) level of theory was used for geometry optimization, vibrational frequency calculations, and dihedral scans. The single-point energies (SPEs) of TEPI and its five radicals were calculated at the MP2/cc-pVXZ (X = D, T, or Q) and CCSD-(T)/cc-pVXZ (X = D, T) levels of theory. We applied complete basis set (CBS) extrapolation to these energies to improve the accuracy and approximate the basis set limit. The bond dissociation energies (BDEs) of TEPI were calculated using single-point energies (SPEs) corrected with zero-point energies (ZPEs), as well as total energies at zero Kelvin (TEZK) obtained from an average of composite methods, including G3B3, G2, CBS-QB3, and G3B3. The thermochemical properties of TEPI and the rate constants for hydrogen atom abstraction (HAA) reactions with molecular oxygen, O