Conformational analysis. 122. Heats of formation of conjugated hydrocarbons by the force field method
Conformational analysis. 122. Heats of formation of conjugated hydrocarbons by the force field method
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构象分析。
DOI：
10.1021/ja00446a001
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发表时间：
1977
影响因子：
15
通讯作者：
N. L. Allinger
中科院分区：
文献类型：
--
作者：
J. Kao;N. L. Allinger
A scheme for the calculation of the heats of formation of conjugated hydrocarbons (gasphase, 25 C) has been de-veloped, which begins with geometries obtained by molecular mechanics calculations. The energies of the part of the molecule (from molecularmechanics) and from the part (from an SCF calculation) are summed to yield the heat of formation. The method is applicable to planar and nonplanar systems of a wide varietyof structural types. The average deviation from ex-periment obtained was 1.34 kcal/mol for a representative group of 65 compounds. This method is far superiorin both generali-ty and in accuracy to any previously published competitive calculational scheme.Although the Pariser-Parr-Pople self-consistent-field molecular-orbital (PPP-SCF-MO) theory of tt electron systems3 has been successfully applied to the prediction of elec-tronic transition energies, 3-4 comparatively few applications of the method have been made to ground state properties. Past calculations of the heats of atomizationAH& or heats of formation (AH f) of conjugated systems have been especially few. Chung and Dewar5 were the first to develop an SCF-MO treatment for the ground state properties of conjugated hy-drocarbons, and this was later modified to some extent. 6 Lo and Whitehead7 and Lorquet8 employed different parameter schemes within their SCF-MO treatments and achieved re-sults for hydrocarbons comparable in accuracy to those obtained by Dewar and co-workers. Two major handicaps of the PPP-SCF-MO method were evident from this work; namely the limitation of the method to planar structures, and its in-ability to allowfor strain and nonbonded interactions. It is surprising that no extensive systematic application of the method including strain and nonbonded interactions has yet been reported. 9Recent applications of SCF methods to the calculation of heats of formation have been mainly of the all valence electron (MINDO) type. 4-10 The force field method has been widely examinedand has proved to be a good method to calculate geometries, steric energies, and heats of formation (AHf) for localized mole-cules. 11 However, there are only two full-scale attempts at grappling with the problem of the use of force field calculations to determine the structures of delocalized molecules that have been reported. Both the Karplus-Warshel12 and our11-13 methods for delocalized molecules work pretty well. The ap-
