Choi Y M, Lin M C
Department of Chemistry, Emory University, 1515 Pierce Drive, Atlanta, Georgia 30322, USA.
Chemphyschem. 2004 Feb 20;5(2):225-32. doi: 10.1002/cphc.200300919.
Kinetics and mechanism for the reaction of phenyl radical (C6H5) with ketene (H2C beta=C alpha=O) were studied by the cavity ring-down spectrometric (CRDS) technique and hybrid DFT and ab initio molecular orbital calculations. The C6H5 transition at 504.8 nm was used to detect the consumption of the phenyl radical in the reaction. The absolute overall rate constants measured, including those for the reaction with CD2CO, can be expressed by the Arrhenius equation k = (5.9 +/- 1.8) x 10(11) exp[-(1160 +/- 100)/T] cm3 mol-1 s-1 over a temperature range of 301-474 K. The absence of a kinetic isotope effect suggests that direct hydrogen abstraction forming benzene and ketenyl radical is kinetically less favorable, in good agreement with the results of quantum chemical calculations at the G2MS//B3LYP6-31G(d) level of theory for all accessible product channels, including the above abstraction and additions to the C alpha, C beta, and O sites. For application to combustion, the rate constants were extrapolated over the temperature range of 298-2500 K under atmospheric pressure by using the predicted transition-state parameters and the adjusted entrance reaction barriers E alpha = E beta = 1.2 kcal mol-1; they can be represented by the following expression in units of cm3 mol-1 s-1: k alpha = 6.2 x 10(19)T-23 exp[-7590/T] and k beta = 3.2 x 10(4)T2.4 exp[-246/T].
采用光腔衰荡光谱（CRDS）技术以及混合密度泛函理论（DFT）和从头算分子轨道计算方法，研究了苯基自由基（C6H5）与乙烯酮（H2Cβ=Cα=O）反应的动力学和反应机理。利用504.8 nm处的C6H5跃迁来检测反应中苯基自由基的消耗情况。所测得的绝对总速率常数，包括与CD2CO反应的速率常数，在301 - 474 K的温度范围内可用阿伦尼乌斯方程k = (5.9 ± 1.8) x 10(11) exp[-(1160 ± 100)/T] cm3 mol-1 s-1表示。动力学同位素效应的缺失表明，直接氢提取生成苯和烯酮基自由基在动力学上不太有利，这与在G2MS//B3LYP6 - 31G(d)理论水平下对所有可及产物通道（包括上述提取以及向Cα、Cβ和O位点的加成）进行量子化学计算的结果高度一致。为了应用于燃烧领域，通过使用预测的过渡态参数和调整后的入口反应势垒Eα = Eβ = 1.2 kcal mol-1，在大气压力下将速率常数外推到298 - 2500 K的温度范围；它们可以用以下单位为cm3 mol-1 s-1的表达式表示：kα = 6.2 x 10(19)T-23 exp[-7590/T] 和kβ = 3.2 x 10(4)T2.4 exp[-246/T]。
