Choi N, Pilling M J, Seakins P W, Wang L
School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK.
Phys Chem Chem Phys. 2006 May 14;8(18):2172-8. doi: 10.1039/b516531h. Epub 2006 Mar 28.
The kinetics of chlorine atom abstractions from normal and selectively deuterated propane and isobutane have been measured at room temperature and 195 K using a laser flash photolysis system, and following the course of the reaction via IR diode laser absorption measurements of HCl product. In conjunction with the kinetic measurements, a comparison of the HCl signal heights from pairs of measurements on normal and selectively deuterated systems has allowed the determination of the branching fractions of the reactions at the primary, secondary (propane) and tertiary (isobutane) positions. The kinetic data (all in units of cm(3) molecule(-1) s(-1)) for the reaction of Cl atoms with propane ((1.22 +/- 0.02) x10(-10), 195 K; (1.22 +/- 0.03) x10(-10) 298 K) and isobutane ((1.52 +/- 0.02) x10(-10), 195 K; (1.25 +/- 0.04) x10(-10), 298 K) are generally in good agreement with literature data. No data are available for comparison with our measurements for the reactions of Cl atoms with CH(3)CD(2)CH(3) ((1.02 +/- 0.03) x10(-10), 195 K; (1.09 +/- 0.02) x10(-10), 298 K) or (CH(3))(3)CD ((1.32 +/- 0.03) x10(-10), 195 K; (1.12 +/- 0.04) x10(-10), 298 K). Rate coefficients at 195 K for the reactions of Cl atoms with ethane ((5.04 +/- 0.08) x10(-11) and n-butane ((2.19 +/- 0.03) x10(-10)) were also measured. The branching fractions for abstraction at the primary position increased with temperature for both propane ((40 +/- 3)% at 195 K to (48 +/- 3)% at 298 K) and isobutane ((49 +/- 4)% at 195 K to (62 +/- 5)% at 298 K). The direct measurements from this study are in good agreement with most calculations based on structure activity relationships.
利用激光闪光光解系统，并通过红外二极管激光吸收测量HCl产物来跟踪反应进程，在室温及195K下测量了氯原子从普通丙烷、选择性氘代丙烷和异丁烷上夺取氢原子的动力学。结合动力学测量，通过比较普通体系和选择性氘代体系的成对测量中HCl信号高度，确定了反应在伯、仲（丙烷）和叔（异丁烷）位置的支化分数。氯原子与丙烷反应（（1.22±0.02）×10⁻¹⁰，195K；（1.22±0.03）×10⁻¹⁰，298K）以及与异丁烷反应（（1.52±0.02）×10⁻¹⁰，195K；（1.25±0.04）×10⁻¹⁰，298K）的动力学数据（单位均为cm³·分子⁻¹·s⁻¹）与文献数据总体吻合良好。对于氯原子与CH₃CD₂CH₃（（1.02±0.03）×10⁻¹⁰，195K；（1.09±0.02）×10⁻¹⁰，298K）或(CH₃)₃CD（（1.32±0.03）×10⁻¹⁰，195K；（1.12±0.04）×10⁻¹⁰，298K）的反应，没有可与我们测量数据作比较的数据。还测量了氯原子与乙烷（（5.04±0.08）×10⁻¹¹）和正丁烷（（2.19±0.03）×10⁻¹⁰）在195K时的反应速率系数。对于丙烷（从195K时的（40±3）%增加到298K时的（48±3）%）和异丁烷（从195K时的（49±4）%增加到298K时的（62±5）%），伯位夺取氢原子的支化分数均随温度升高而增加。本研究的直接测量结果与大多数基于构效关系的计算结果吻合良好。
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