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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Thermochemical properties for isooctane and carbon radicals: Computational study
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Thermochemical properties for isooctane and carbon radicals: Computational study

机译：异辛烷和碳自由基的热化学性质：计算研究

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摘要

Thermochemical properties for isooctane, its internal rotation conformers, and radicals with corresponding bond energies are determined by use of computational chemistry. Enthalpies of formation are determined using isodesmic reactions with B3LYP density function theory and composite CBS-QB3 methods. Application of group additivity with comparison to calculated values is illustrated. Entropy and heat capacities are determined using geometric parameters, internal rotor potentials, and frequencies from B3LYP/6-31G(d,p) calculations for the lowest energy conformer. Internal rotor potentials are determined for the isooctane parent and for the primary, secondary, and tertiary radicals in order to identify isomer energies. Intramolecular interactions are shown to have a significant effect on the enthalpy of formation of the isooctane parent and its radicals. The computed standard enthalpy of formation for the lowest energy conformers of isooctane from this study is-54.40 ± 1.60 kcal mol~（-1）, which is 0.8 kcal mol~（-1） lower than the evaluated experimental value-53.54 ± 0.36 kcal mol~（-1）. The standard enthalpy of formation for the primary radical for a methyl on the quaternary carbon is-5.00 ± 1.69 kcal mol~（-1）, for the primary radical on the tertiary carbon is-5.18 ± 1.69 kcal mol~（-1), for the secondary isooctane radical is-9.03 ± 1.84 kcal mol~(-1), and for the tertiary isooctane radical is-12.30 ± 2.02 kcal mol ~(-1). Bond energy values for the isooctane radicals are 100.64 ± 1.73, 100.46 ± 1.73, 96.41 ± 1.88 and 93.14 ± 2.05 kcal mol~(-1) for C3?CCCC2, C3CCCC2?, C3CC?CC2, and C3CCC?C2, respectively. Entropy and heat capacity values are reported for the lowest energy homologues.
机译：异辛烷，其内部旋转构象异构体以及具有相应键能的自由基的热化学性质可通过计算化学方法确定。使用B3LYP密度函数理论和复合CBS-QB3方法通过等渗反应确定生成焓。说明了组可加性与计算值比较的应用。熵和热容量使用几何参数，内部转子电势和B3LYP / 6-31G（d，p）计算得出的频率来确定，其能量最低。确定异辛烷母体以及伯，仲和叔基的内部转子电势，以识别异构体能。分子内相互作用显示出对异辛烷母体及其自由基形成焓具有显着影响。这项研究计算出的异辛烷最低能构象的标准形成焓为-54.40±1.60 kcal mol〜（-1），比评估的实验值-53.54±0.36 kcal低0.8 kcal mol〜（-1）。摩尔〜（-1）。季碳上一个甲基的伯基的标准形成焓为-5.00±1.69 kcal mol〜（-1），叔碳上的伯基的形成焓为-5.18±1.69 kcal mol〜（-1），仲异辛烷基的自由基为-9.03±1.84 kcal mol〜（-1），叔异辛烷基的自由基为-12.30±2.02 kcal mol〜（-1）。对于C3→CCCC2，C3CCCC2→，C3CC→CC2和C3CCC→C2，异辛烷基的键能值为100.64±1.73、100.46±1.73、96.41±1.88和93.14±2.05kcal mol·（-1）。报告了最低能量同系物的熵和热容值。

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