Snitsiriwat Suarwee, Bozzelli Joseph W
Department of Chemistry and Environmental Science, New Jersey Institute of Technology , University Heights, Newark, New Jersey 07102 United States.
J Phys Chem A. 2014 Jul 3;118(26):4631-46. doi: 10.1021/jp502702f. Epub 2014 Jun 19.
Thermochemical properties of tert-isooctane hydroperoxide and its radicals are determined by computational chemistry. Enthalpies are determined using isodesmic reactions with B3LYP density function and CBS QB3 methods. Application of group additivity with comparison to calculated values is illustrated. Entropy and heat capacities are determined using geometric parameters and frequencies from the B3LYP/6-31G(d,p) calculations for the lowest energy conformer. Internal rotor potentials are determined for the tert-isooctane hydroperoxide and its radicals in order to identify isomer energies. Recommended values derived from the most stable conformers of tert-isooctane hydroperoxide of are -77.85 ± 0.44 kcal mol(-1). Isooctane is a highly branched molecule, and its structure has a significant effect on its thermochemistry and reaction barriers. Intramolecular interactions are shown to have a significant effect on the enthalpy of the isooctane parent and its radicals on peroxy/peroxide systems, the R• + O2 well depths and unimolecular reaction barriers. Bond dissociation energies and well depths, for tert-isooctane hydroperoxide → R• + O2 are 33.5 kcal mol(-1) compared to values of ∼38 to 40 kcal mol(-1) for the smaller tert-butyl-O2 → R• + O2. Transition states and kinetic parameters for intramolecular hydrogen atom transfer and molecular elimination channels are characterized to evaluate reaction paths and kinetics. Kinetic parameters are determined versus pressure and temperature for the chemically activated formation and unimolecular dissociation of the peroxide adducts. Multifrequency quantum RRK (QRRK) analysis is used for k(E) with master equation analysis for falloff. The major reaction paths at 1000 K are formation of isooctane plus HO2 followed by cyclic ether plus OH. Stabilization of the tert-isooctane hydroperoxy radical becomes important at lower temperatures.
叔异辛基过氧化氢及其自由基的热化学性质通过计算化学来确定。使用具有B3LYP密度函数的等键反应和CBS QB3方法来确定焓。说明了基团加和性的应用以及与计算值的比较。熵和热容使用最低能量构象体的B3LYP/6 - 31G(d,p)计算得到的几何参数和频率来确定。为了确定异构体能量，还测定了叔异辛基过氧化氢及其自由基的内转子势能。从叔异辛基过氧化氢最稳定构象体得出的推荐值为-77.85±0.44千卡/摩尔(-1)。异辛烷是一种高度支化的分子，其结构对其热化学和反应势垒有显著影响。分子内相互作用对异辛烷母体及其在过氧/过氧化物体系中的自由基的焓、R• + O2阱深和单分子反应势垒有显著影响。叔异辛基过氧化氢→R• + O2的键离解能和阱深为33.5千卡/摩尔(-1)，相比之下较小的叔丁基 - O2→R• + O2的值约为38至40千卡/摩尔(-1)。对分子内氢原子转移和分子消除通道的过渡态和动力学参数进行了表征，以评估反应路径和动力学。确定了过氧化物加合物化学活化形成和单分子解离的动力学参数与压力和温度的关系。多频量子RRK（QRRK）分析用于k(E)，并结合主方程分析来研究反应速率的衰减。1000 K时的主要反应路径是形成异辛烷加HO2，然后是环醚加OH。在较低温度下，叔异辛基氢过氧自由基的稳定化变得很重要。
