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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Thermochemistry of C_7H_(16) to C_(10)H_(22) Alkane Isomers: Primary, Secondary, and Tertiary C-H Bond Dissociation Energies and Effects of Branching
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Thermochemistry of C_7H_(16) to C_(10)H_(22) Alkane Isomers: Primary, Secondary, and Tertiary C-H Bond Dissociation Energies and Effects of Branching

机译：C_7H_（16）到C_（10）H_（22）烷烃异构体的热化学：一级，二级和三级C-H键解离能及支化作用

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Standard enthalpies of formation (ΔH°_(f 298)) of methyl, ethyl, primary and secondary propyl, and n-butyl radicals are evaluated and used in work reactions to determine internal consistency. They are then used to calculate the enthalpy of formation for the tert-butyl radical. Other thermochemical properties including standard entropies (S°(T)), heat capacities (C_p(T)), and carbon-hydrogen bond dissociation energies (C-H BDEs) are reported for n-pentane, n-heptane, 2-methylhexane, 2,3-dimethylpentane, and several branched higher carbon number alkanes and their radicals. ΔH°_(f 298) and C-H BDEs are calculated using isodesmic work reactions at the B3LYP (6-31G(d,p) and 6-311G(2d,2p) basis sets), CBSQB3, CBS-APNO, and G3MP2B3 levels of theory. Structures, moments of inertia, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level for contributions to entropy and heat capacities. Enthalpy calculations for these hydrocarbon radical species are shown to have consistency with the CBS-QB3 and CBS-APNO methods using all work reactions. Our recommended ideal gas phase ΔH°_(f 298) values are from the average of all CBS-QB3, CBS-APNO, and for G3MP2B3, only where the reference and target radical are identical types, and are compared with literature values. Calculated values show agreement between the composite calculation methods and the different work reactions. Secondary and tertiary C-H bonds in the more highly branched alkanes are shown to have bond energies that are several kcal mol~(-1) lower than the BDEs in corresponding smaller molecules often used as reference species. Entropies and heat capacities are calculated and compared to literature values (when available) when all internal rotors are considered.
机译：评估甲基，乙基，伯和仲丙基，正丁基和正丁基的标准形成焓（ΔH°（f 298）），并将其用于工作反应以确定内部稠度。然后将它们用于计算叔丁基自由基的形成焓。报告了正戊烷，正庚烷，2-甲基己烷，2的其他热化学性质，包括标准熵（S°（T）），热容（C_p（T））和碳氢键解离能（CH BDEs）。 ，3-二甲基戊烷和一些支链的较高碳数的烷烃及其自由基。使用B3LYP（6-31G（d，p）和6-311G（2d，2p）基组），CBSQB3，CBS-APNO和G3MP2B3水平的等离子功反应计算ΔH°_（f 298）和CH BDEs理论。在B3LYP / 6-31G（d，p）级别上计算结构，惯性矩，振动频率和内部转子电势，以有助于熵和热容量。这些烃自由基物种的焓计算显示与使用所有工作反应的CBS-QB3和CBS-APNO方法具有一致性。我们建议的理想气相ΔH°_（f 298）值来自所有CBS-QB3，CBS-APNO和G3MP2B3的平均值，仅当参考基团和目标基团是相同类型时，才与文献值进行比较。计算值表明复合计算方法与不同的工作反应之间的一致性。支化度更高的烷烃中的二级和三级C-H键的键能比通常用作参考物质的相应较小分子中的BDE低几千卡·摩尔（-1）。当考虑所有内部转子时，将计算熵和热容量并将其与文献值（如果有）进行比较。

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