Gao Yide, DeYonker Nathan J, Garrett E Chauncey, Wilson Angela K, Cundari Thomas R, Marshall Paul
The Department of Chemistry, Center for Advanced Scientific Computing and Modeling, University of North Texas, 1155 Union Circle No. 305070, Denton, Texas 76203-5017, USA.
J Phys Chem A. 2009 Jun 25;113(25):6955-63. doi: 10.1021/jp901314y.
A quantitative understanding of the thermochemistry of cyclohexadienyl radical and 1,4-cyclohexadiene is beneficial for diverse areas of chemistry. Given the interest in these two species, it is surprising that more detailed thermodynamic data concerning the homolytic C-H bond enthalpies of such entities have not been forthcoming. We thus undertook an experimental and computational evaluation of (a) the enthalpy of formation of cyclohexadienyl radical (C(6)H(7)), (b) the homolytic C-H bond enthalpy of 1,4-cyclohexadiene (C(6)H(8)), and (c) the enthalpy of the addition of a hydrogen atom to benzene. Using laser photolysis experiments coupled with highly accurate ab initio quantum mechanical techniques, a newly recommended enthalpy of formation for C(6)H(7) is determined to be 208.0 +/- 3.9 kJ mol(-1), leading to a homolytic bond dissociation enthalpy of 321.7 +/- 2.9 kJ mol(-1), almost 9 kJ mol(-1) higher than previously determined enthalpies that used less certain experimental values for the C(6)H(7) enthalpy of formation.
对环己二烯基自由基和1,4 - 环己二烯热化学的定量理解对化学的多个领域都有益处。鉴于对这两种物质的关注，令人惊讶的是，关于此类实体均裂C - H键焓的更详细热力学数据尚未出现。因此，我们对以下内容进行了实验和计算评估：(a) 环己二烯基自由基（C₆H₇）的生成焓；(b) 1,4 - 环己二烯（C₆H₈）的均裂C - H键焓；(c) 氢原子加成到苯上的焓变。通过结合高精度从头算量子力学技术的激光光解实验，确定C₆H₇新推荐的生成焓为208.0±3.9 kJ mol⁻¹，导致均裂键解离焓为321.7±2.9 kJ mol⁻¹，比之前使用不太确定的C₆H₇生成焓实验值所确定的焓高出近9 kJ mol⁻¹。
