Valadbeigi Younes, Farrokhpour Hossein, Tabrizchi Mahmoud
Department of Chemistry, Isfahan University of Technology , Isfahan 84156-83111, Iran.
J Phys Chem A. 2014 Sep 11;118(36):7663-71. doi: 10.1021/jp506140m. Epub 2014 Aug 26.
A kinetic study was performed on the proton-bound dimer formation of cyclopentanone, cyclohexanone, and cycloheptanone at atmospheric pressure with ion mobility spectrometry (IMS) at the temperature range of 30 to 70 °C. Measured rate constants were in the range of 9.5 × 10(-11) to 4.5 × 10(-10) cm(3) s(-1). Rate constants were also calculated using average dipole orientation (ADO) theory employing density functional theory (DFT). Calculated rate constants were in the range of 1.0-5.5 × 10(-9) cm(3) s(-1). The difference between experimental and calculated rate constants was interpreted based on the hydration of the protonated monomers so that water molecules were replaced with a neutral monomer molecule in the process of dimer formation. This process requires activation energy for the formation of dimer and consequently reduces the rate constants. To verify our hypothesis, an effective rate constant (keff) was introduced, which accounted for the energetically activated water-monomer replacement in the dimer formation reactions. A good agreement was observed between the experimental rate constants and calculated keff, confirming the validity of the proposed model in explaining the kinetics of dimer formation in atmospheric pressure.
在30至70°C的温度范围内，利用离子迁移谱（IMS）在大气压下对环戊酮、环己酮和环庚酮的质子结合二聚体形成进行了动力学研究。测得的速率常数在9.5×10⁻¹¹至4.5×10⁻¹⁰ cm³ s⁻¹范围内。还使用采用密度泛函理论（DFT）的平均偶极取向（ADO）理论计算了速率常数。计算得到的速率常数在1.0 - 5.5×10⁻⁹ cm³ s⁻¹范围内。基于质子化单体的水合作用解释了实验速率常数与计算速率常数之间的差异，即在二聚体形成过程中水分子被中性单体分子取代。该过程需要活化能来形成二聚体，因此降低了速率常数。为了验证我们的假设，引入了有效速率常数（keff），它考虑了二聚体形成反应中能量活化的水 - 单体取代。实验速率常数与计算得到的keff之间观察到良好吻合，证实了所提出模型在解释大气压下二聚体形成动力学方面的有效性。
