Galano Annia
Instituto Mexicano del Petróleo, Eje Central Lazaro Cardenas 152, 007730 México DF, México.
J Phys Chem A. 2006 Jul 27;110(29):9153-60. doi: 10.1021/jp061705b.
A theoretical study of the mechanism and kinetics of the OH hydrogen abstraction from hydroxyacetone is presented. Optimum geometries and frequencies have been computed at the BH and HLYP/6-311++G(d,p) level of theory for all stationary points. Energy values have been improved by single-point calculations at the above geometries using CCSD(T)/ 6-311++G(d,p). The rate coefficients are calculated for the temperature range 280-500 K by using conventional transition state theory (TST), including tunneling corrections. Our analysis supports a stepwise mechanism involving the formation of a reactant complex in the entrance channel and a product complex in the exit channel, for all the modeled paths. Four experimental values of the rate constant at 298 K have been previously reported: three of them in great agreement (approximately 3 x 10(-12) cm(3) molecule(-1) s(-1)), and one of them twice larger. The calculations in the present work support the smaller value. A curved Arrhenius plot was found in the studied temperature range; thus the expression that best describes the obtained data is k(280-500)(overall) = 5.29 x 10(-23)T(3.4)e(1623/T) cm(3) molecule(-1) s(-1). The activation energy was found to vary with temperature from -1.33 to +0.15 kcal/mol.
本文对从羟基丙酮中夺取氢原子的OH反应机理和动力学进行了理论研究。在BH和HLYP/6-311++G(d,p)理论水平上计算了所有驻点的最优几何结构和频率。通过在上述几何结构上使用CCSD(T)/6-311++G(d,p)进行单点计算，提高了能量值。使用传统过渡态理论（TST），包括隧穿校正，计算了280 - 500 K温度范围内的速率系数。对于所有模拟路径，我们的分析支持一种逐步机理，该机理涉及在入口通道形成反应物络合物以及在出口通道形成产物络合物。先前已报道了298 K时速率常数的四个实验值：其中三个非常吻合（约为3×10⁻¹² cm³·分子⁻¹·s⁻¹），另一个是其两倍大。本工作中的计算支持较小的值。在所研究的温度范围内发现了一条弯曲的阿伦尼乌斯曲线；因此，最能描述所得数据的表达式为k(280 - 500)(总体) = 5.29×10⁻²³T³·⁴e¹⁶²³/T cm³·分子⁻¹·s⁻¹。发现活化能随温度在 - 1.33至 + 0.15 kcal/mol之间变化。
