计算饱和醇异构体标准生成焓的新方法

基于极性叠加原理,在成功设计烷烃异构体和多氯代烷烃生成焓计算新方法的基础上,设计了一种计算多元醇异构体生成焓的新方法,并合理地假定任一异构体的原子化焓等于三种键(C-C、C-H和C-O-H键)的键能、极性叠加能项以及氢键能项的加和.用这一模型拟合24种原子化焓数据,得到了标准生成焓的估算公式.为了检验预测的精确性,又设计了一种预测方法,使用在排除被预测的化合物条件下回归得到的参数,预测该化合物的生成焓.按这种方法,预测了24种异构体的生成焓.通过该5参数预测的相对于实验值的各种误差(平均绝对误差、均方根误差和最大绝对误差)不仅比7参数的基团法预测的对应误差小得多,而且比相应实验数据的误差还要小.与键加和法比较,该方法的模型包含了极性叠加能和氢键能量,该两项代表了主要的非键相互作用能,表征了不同异构体的结构差异,并大大减少了参数.

A New Scheme for Calculating the Standard Enthalpies of Formation of Alkanol Isomers

On the basis of successfully designing the schemes for calculation of the enthalpies of formation of alkane isomers and polychlorocarbon isomers applying the idea of polarity interference, we now design a new scheme for calculating the enthalpies of formation of polyhydric alcohol isomers. In this scheme, we reasonably suppose the enthalpy of atomization of any isomer to be equal to the sum of three bond enthalpy terms (i.e., C-C, C-H and C-O-H bond enthalpy terms) and a polarity interference enthalpy term and a hydrogen bond enthalpy term. Fitting such a model to 24 data of enthalpies of atomization of 24 compounds, an estimation formula for their enthalpies of formation has been obtained. In order to test the prediction accuracy, we have designed a predication method in which using the parameters obtained under exclusion of the compound to be predicted at each time, we predict the enthalpy of formation of the compound. According to such a method, the enthalpies of formation for the 24 isomers have been predicted. The average absolute errors from corresponding experimental values, root mean square deviation, and the max absolute errors predicted by this scheme with 5 parameters are not only much less than those predicted by the group scheme with 7 parameters, but also less than the corresponding deviations of experimental data. Compared with other bond additivity schemes for calculation of the enthalpies of formation of compounds, a very important advantage of this new scheme is that its model contains the polarity interference enthalpy and hydrogen bond enthalpy terms well reflecting main non-bonded interaction energies and expressing the structural disparities among different isomers, and greatly reducing parameters.