Cruz-Torres Armando, Galano Annia, Alvarez-Idaboy J Raúl
Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas 152, 007730 México D. F., México.
Phys Chem Chem Phys. 2006 Jan 14;8(2):285-92. doi: 10.1039/b507101a. Epub 2005 Oct 19.
The OH hydrogen abstraction reaction from beta-alanine has been studied using the BHandHLYP hybrid HF-density functional and 6-311G(d,p) basis sets. The energies have been improved by single point calculations at the CCSD(T)/6-311G(d,p) level of theory. The structures of the different stationary points are discussed. Reaction profiles are modeled including the formation of pre-reactive and product complexes. Negative net activation energy is obtained for the overall reaction. A complex mechanism is proposed, and the rate coefficients are calculated using transition state theory over the temperature range of 250-400 K. The rate coefficients are proposed for the first time and it was found that in the gas phase the hydrogen abstraction occurs mainly from the CH(2) group next to the amino end. The following expressions, in cm(3) mol(-1) s(-1), are obtained for the overall rate constants, at 250-400 and 290-310 K, respectively: k(250-400)= 2.36 x 10(-12) exp(340/T), and k(290-310)= 1.296 x 10(-12) exp(743/T). The three parameter expression that best describes the studied reaction is k(250-400)= 1.01 x 10(-21)T(3.09) exp(1374/T). The beta-alanine + OH reaction was found to be 1.5 times faster than the alpha-alanine + OH reaction.
使用BHandHLYP杂化HF-密度泛函和6-311G(d,p)基组研究了从β-丙氨酸中夺取OH氢的反应。通过在CCSD(T)/6-311G(d,p)理论水平上进行单点计算提高了能量。讨论了不同驻点的结构。对反应剖面进行了建模，包括预反应复合物和产物复合物的形成。得到了整个反应的负净活化能。提出了一个复杂的机理，并使用过渡态理论在250-400 K的温度范围内计算了速率系数。首次提出了速率系数，发现在气相中氢夺取主要发生在氨基端旁边的CH(2)基团上。分别在250-400 K和290-310 K下得到了以下总速率常数的表达式，单位为cm(3) mol(-1) s(-1)：k(250-400)= 2.36 x 10(-12) exp(340/T)，k(290-310)= 1.296 x 10(-12) exp(743/T)。最能描述所研究反应的三参数表达式为k(250-400)= 1.01 x 10(-21)T(3.09) exp(1374/T)。发现β-丙氨酸+OH反应比α-丙氨酸+OH反应快1.5倍。
