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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Theoretical Bond Energies: A Critical Evaluation
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Theoretical Bond Energies: A Critical Evaluation

机译：理论键能：关键评估

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摘要

The recently proposed scheme of Grimme (BE scheme) (I. Am. Chem. Sor. 1996, 118, 1529) to calculate intrinsic bond energies (BE's) of hydrocarbons, which define seminal equilibrium quantities of chemical structures, is evaluated critically. CH and regular CC bonds are treated well; the corresponding BE's are reliable and self-consistent. In contrast, the performance of the method is markedly reduced for bonds of unusual1ength, if the bond length is not determined by bond bending or by conjugation. Differences between BE's for CH bonds, which lie within the remarkably narrow range from ca. 103 to 110 kcal mol-l, and CH bond dissociation energies (BDE's,ca. 86-132 kcal mol-l, linear correlation,Rc = 0.9291) give a measure of radical (de)stabilization. BE's of SpT-SpY CC single bonds correlate linearly with the respective BDE's (Rc = 0.9987) and can be used tor a reliable prediction of BDE's at almost no computational cost. Individual intrinsic bond energies are used to establish CC and CH bond length-bond energy-bond order correlations. In extension of Grimme' s original report, the performance of the model is tested thoroughly for anions, cations, and radicals of hydrocarbons and it is shown that these species are treated less satisfactorily ..Attempts to treat non-hydrocarbon compounds by the same procedure are also less successful with the exception of saturated silicon hydrides. Results of this work show that the relationships between bond length-bond order-bond energy as described by established models of the chemical bond can be related to the properties of the electron density at bond critical points. Despite the much greater angle distortion, cyclopropane has a strain energy only slightly larger than cyclobutane. This problem of the nearly equivalent strain energies is readdressed, leading to new estimates for the stabilization of cyclopropane due to CH bond strengthening (11.7 kcal mol-l) and to a-aromaticity (11.3kcalmol;-I).
机译：严格评估了最近提出的Grimme方案（BE方案）（I。Am。Chem。Sor。1996，118，1529），该方案用于计算烃的固有键能（BE's），定义了化学结构的精平衡量。 CH和常规CC债券得到良好处理;相应的BE可靠且自洽。相反，如果粘结长度不是通过粘结弯曲或通过共轭确定的，则对于异常强度的粘结，该方法的性能会显着降低。 CH键的BE之间的差异位于ca的极窄范围内。 103至110 kcal mol-1，CH键解离能（BDE's，约86-132 kcal mol-1，线性相关，Rc = 0.9291）给出了自由基（去）稳定度的量度。 SpT-SpY CC单键的BE与相应的BDE线性相关（Rc = 0.9987），可用于几乎无计算成本的BDE可靠预测。各个内在键能用于建立CC和CH键的长度键能键顺序相关性。在Grimme的原始报告的扩展中，对该模型的性能进行了彻底的烃阴离子，阳离子和自由基测试，结果表明这些物种的处理效果不令人满意。尝试通过相同的方法处理非烃化合物除饱和氢化硅外，它们的成功率也较低。这项工作的结果表明，化学键的已建立模型所描述的键长-键序-键能之间的关系可以与键临界点处电子密度的性质有关。尽管角度畸变大得多，但环丙烷的应变能仅比环丁烷稍大。这个几乎相等的应变能的问题被重新解决，由于CH键的增强（11.7kcal mol-1）和α-芳烃性（11.3kcalmol; -1），导致对环丙烷稳定的新估计。

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