Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, USA.
J Phys Chem A. 2009 Dec 10;113(49):13762-71. doi: 10.1021/jp904232n.
All species involved in the multichannel decomposition of gas-phase dimethyl methylphosphonate (DMMP) were investigated by electronic structure calculations. Geometries for stationary structures along the reaction paths, were fully optimized with the MP2 method and the B3LYP and MPW1K DFT functionals, and the 6-31G*, 6-31++G**, and aug-cc-pVDZ basis sets. The geometries determined by the B3LYP and MPW1K functionals are in very good agreement with the MP2 values. Increasing the basis set size from 6-31G* to aug-cc-pVDZ does not significantly alter this result. Single point energy calculations were carried out with highly accurate but computationally more expensive CBS-QB3 theory. DMMP has three conformers, which lead to the four primary product channels, (O)P(CH(2))(OCH(3)) + CH(3)OH, (O)P(CH(3)) (OCH(3))(OH) + CH(2), c-(O)P(CH(3))OCH(2) + CH(3)OH, and (O)P(CH(3))(OCH(3))(OCH) + H(2). The first channel has the lowest energy barrier and is expected to be the most important pathway. It occurs via C-H and P-O bond cleavages accompanied by O-H bond formation. The other three channels have higher and similar energy barriers, and are expected to have smaller and similar rates. The product (O)P(CH(3))(OCH(3))(OCH) undergoes a secondary decomposition to form (OH)P(CH(3))(OCH(3)) + CO.
所有涉及气相二甲基甲基膦酸酯（DMMP）多通道分解的物种都通过电子结构计算进行了研究。通过 MP2 方法以及 B3LYP 和 MPW1K DFT 函数，用 6-31G*、6-31++G** 和 aug-cc-pVDZ 基组对反应路径上的稳定结构的几何形状进行了完全优化。B3LYP 和 MPW1K 函数确定的几何形状与 MP2 值非常吻合。将基组从 6-31G*增加到 aug-cc-pVDZ 并不会显著改变这一结果。单点能计算采用了高度准确但计算成本更高的 CBS-QB3 理论进行。DMMP 有三个构象，导致了四个主要的产物通道，(O)P(CH(2))(OCH(3)) + CH(3)OH、(O)P(CH(3)) (OCH(3))(OH) + CH(2)、c-(O)P(CH(3))OCH(2) + CH(3)OH 和 (O)P(CH(3))(OCH(3))(OCH) + H(2)。第一个通道的能量势垒最低，预计是最重要的途径。它通过 C-H 和 P-O 键的断裂以及 O-H 键的形成发生。其他三个通道的能量势垒较高且相似，预计其反应速率也较小且相似。产物 (O)P(CH(3))(OCH(3))(OCH) 会发生二次分解，形成 (OH)P(CH(3))(OCH(3)) + CO。
