GROUND STATES OF CONJUGATED MOLECULES .9. HYDROCARBON RADICALS AND RADICAL IONS
GROUND STATES OF CONJUGATED MOLECULES .9. HYDROCARBON RADICALS AND RADICAL IONS
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DOI：
10.1021/ja01010a005
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发表时间：
1968-01-01
影响因子：
15
通讯作者：
VENIER, CG
中科院分区：
文献类型：
--
作者：
DEWAR, MJS;HASHMALL, JA;VENIER, CG
本系列文献4中所述的SCF-MO方法已推广到开壳体系，特别是碳氢自由基和自由基离子。计算是通过改进的闭壳层程序进行的，其中未成对的电子被两个自旋相反的半电子取代。计算结果与偶数交替烃的自由基生成热、电子亲和能和电离势的实验数据符合得很好，也表明光谱电离常数和电子碰撞电离常数的差异是由于前者是绝热值，后者是垂直值。给出了半电子模型的理论证明，并用它解释了PMO方法的成功。5用分子轨道理论讨论共轭自由基的生成热，目前仅限于粗略的HMO计算。这篇文章的目的是提出一种SCF-MO方法，它似乎对广泛的碳氢自由基和自由基离子都能得到非常满意的结果。这种方法的基础是Pople SCF MO方法的一个版本，该方法已在本系列的早期文献4中描述，并已被证明对大范围的闭壳型共轭分子1·4·6的基态性质的计算具有极高的精度。本文对该方法作了简单的修正，使其适用于开壳系统，取得了类似的结果。这里讨论的自由基是碳氢基，如烯丙基或苄基，以及由中性碳氢化合物通过电子的损失或获得而产生的离子自由基。近年来已经测量了各种自由基的生成热；离子的生成热可以从母体碳氢化合物的生成热以及实验确定的电离势或电子亲和能来推断。以前计算电离势或电子亲合势的大多数尝试都是基于库普曼斯定理。7由于即将成为父母的原因，本程序不适用于此。然而，我们的方法提供了离子自由基形成热的直接估计，与对母体碳氢化合物的类似估计一起，允许计算电离势和电子亲和能。由于我们的程序现在准确地给出了中性碳氢化合物的生成热
The SCF-MO method described in previous papers4 of this series has been extended to open-shell sys-tems, in particularhydrocarbon radicals and radical ions. The calculations were carried out by a modified closedshell procedure in which the unpaired electron is replaced by two half-electrons of opposite spin. The results are in goodagreement with experimentaldata for the heats of formation of radicals and electron affinities and ionization potentials of even-alternant hydrocarbons; theyalso suggest that the differences between spectroscopic and electron-impact values for ionization constants are due to the former being adiabatic values, and the latter vertical ones. A theoretical justification for the half-electron model is given, and it is also used to explain the success of the PMO method. 5Attempts to discuss the heats of formation of con-xx jugated radicals in terms of MO theory have until now been limited to crude HMO calculations. The purpose of this paper is to present a SCF-MO treatment which seems to give very satisfactory results for a wide range of hydrocarbon radicals and radical ions. The basis of this approach is a version of the Pople SCF MO method which has beendescribed in earlier papers4 of this series, and which has beenshown to account with remarkable accuracy for the ground-state proper-ties of a wide range of conjugated molecules1· 4· 6 of closed-shell type. Here we describe a simple modifica-tion of the method which allows it to be applied with similar success to open-shell systems. The radicals treated here are hydrocarbon radicals, such as allyl or benzyl, and ion radicals derived from neutral hydrocarbons by loss, or gain, of an electron. The heats of formation of various radicals have been measured in recent years; those of the ions can be inferred from the heats of formation of the parent hydro-carbons, together with the experimentally determined ionization potentials or electron affinities. Most pre-vious attempts to calculate ionization potentials or electron affinities havebeen based on the use of Koop-mans’ theorem. 7 For reasons that will become ap-parent presently, this procedure is not applicable here. However, our method provides direct estimates of the heats of formation of the ion radicals, which, together with similar estimates for the parent hydrocarbons, allow the ionization potentials and electron affinities to be calculated. Since our procedure now gives heats of formation of neutral hydrocarbons with an accuracy