Wang Heng, Castillo Álvaro, Bozzelli Joseph W
Department of Chemical Engineering, Chemistry, and Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States.
J Phys Chem A. 2015 Jul 23;119(29):8202-15. doi: 10.1021/acs.jpca.5b03912. Epub 2015 Jul 1.
Enthalpies of formation for 14 C2–C4 fluorinated hydrocarbons were calculated with nine popular ab initio and density functional theory methods: B3LYP, CBS-QB3, CBS-APNO, M06, M06-2X, ωB97X, G4, G4(MP2)-6X, and W1U via several series of isodesmic reactions. The recommended ideal gas phase ΔHf298° (kcal mol(–1)) values calculated in this study are the following: −65.4 for CH3CH2F; −70.2 for CH3CH2CH2F; −75.3 for CH3CHFCH3; −75.2 for CH3CH2CH2CH2F; −80.3 for CH3CHFCH2CH3; −108.1 for CH2F2; −120.9 for CH3CHF2; −125.8 for CH3CH2CHF2; −133.3 for CH3CF2CH3; −166.7 for CHF3; −180.5 for CH3CF3; −185.5 for CH3CH2CF3; −223.2 for CF4; and −85.8 for (CH3)3CF. Entropies (S298° in cal mol(–1) K(–1)) were estimated using B3LYP/6-31+G(d,p) computed frequencies and geometries. Rotational barriers were determined and hindered internal rotational contributions for S298°, and Cp(T) were calculated using the rigid rotor harmonic oscillator approximation, with direct integration over energy levels of the intramolecular rotation potential energy curve. Thermochemical properties for the fluorinated carbon groups C/C/F/H2, C/C2/F/H, C/C/F2/H, C/C2/F2, and C/C/F3 were derived from the above target fluorocarbons. Previously published enthalpies and groups for 1,2-difluoroethane, 1,1,2-trifluoroethane, 1,1,2,2-tetrafluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,1,2,2-pentafluoroethane, 2-fluoro-2-methylpropane that were previously determined via work reaction schemes are revised using updated reference species values. Standard deviations are compared for the calculation methods.
通过一系列等键反应，使用九种常用的从头算和密度泛函理论方法：B3LYP、CBS-QB3、CBS-APNO、M06、M06-2X、ωB97X、G4、G4(MP2)-6X和W1U，计算了14种C2 - C4氟代烃的生成焓。本研究计算得到的推荐理想气相ΔHf298°（千卡·摩尔⁻¹）值如下：CH3CH2F为 - 65.4；CH3CH2CH2F为 - 70.2；CH3CHFCH3为 - 75.3；CH3CH2CH2CH2F为 - 75.2；CH3CHFCH2CH3为 - 80.3；CH2F2为 - 108.1；CH3CHF2为 - 120.9；CH3CH2CHF2为 - 125.8；CH3CF2CH3为 - 133.3；CHF3为 - 166.7；CH3CF3为 - 180.5；CH3CH2CF3为 - 185.5；CF4为 - 223.2；(CH3)3CF为 - 85.8。使用B3LYP/6 - 31 + G(d,p)计算的频率和几何结构估算熵（S298°，单位为卡·摩尔⁻¹·K⁻¹）。确定了旋转势垒，并使用刚性转子谐振子近似计算了S298°和Cp(T)的受阻内旋转贡献，对分子内旋转势能曲线的能级进行直接积分。从上述目标氟代烃中推导了氟代碳基团C/C/F/H2、C/C2/F/H、C/C/F2/H、C/C2/F2和C/C/F3的热化学性质。使用更新后的参考物种值，对先前通过工作反应方案确定的1,2 - 二氟乙烷、1,1,2 - 三氟乙烷、1,1,2,2 - 四氟乙烷、1,1,1,2 - 四氟乙烷、1,1,1,2,2 - 五氟乙烷、2 - 氟 - 2 - 甲基丙烷的生成焓和基团进行了修订。比较了计算方法的标准偏差。
