Approximate self-consistent molecular orbital theory of nuclear spin coupling. I. Directly bonded carbon-hydrogen coupling constants
Approximate self-consistent molecular orbital theory of nuclear spin coupling. I. Directly bonded carbon-hydrogen coupling constants
复制标题
核自旋耦合的近似自洽分子轨道理论。
DOI：
10.1021/ja00704a001
复制
发表时间：
1970
影响因子：
15
通讯作者：
J. Pople
中科院分区：
文献类型：
--
作者：
G. Maciel;J. McIver;N. Ostlund;J. Pople
采用有限微扰方法，在INDO分子轨道近似下，应用自洽微扰理论，计算了一系列分子中直接成键的碳和氢之间的各向同性核自旋耦合。包括只与费米接触机制的扰动，JCH值计算各种各样的化合物。以氢原子和碳原子的原子轨道密度为固定参数，对于烃和具有-1+取代基（-F，-OR，-NR 2，-O等）的分子，得到了与实验趋势很好的一致性，但不适用于具有-I-取代基（-CF 3、-C（O）X、-NO2、-CN等）的分子。当这些密度按照基于斯莱特规则的简单修正而变化时，计算结果和实验结果之间的对应关系得到了定性的改善。对于那些实验趋势被定性再现的分子，预测取代基效应的敏感性比基于碳的性质的简单参数所预测的更接近实验结果。核自旋-自旋耦合常数中研究最频繁的一类，也是在定性理论争论中出现得相当频繁的一类，是直接键合的CH常数。通过卫星实验和有趣的早期碳杂化解释的相对直接的实验访问产生了大量的实验活动针对这一nmr参数。2-20早期的杂交论点是
With the employment of finite perturbation methods, a self-consistent perturbation theory is applied in the INDO molecular orbital approximation to the calculation of isotropic nuclear spin coupling between directly bonded carbon and hydrogen for a series of molecules. Including perturbations associated only with the Fermi contact mechanism, Jch values are calculated for a wide variety of compounds. Regarding hydrogen Is and carbon 2s atomic orbital densities at the nuclei as fixed parameters, good agreement with experimental trends is obtained for hydrocarbons and for molecules with—1+ substituents (-F,-OR,-NR2,—O, etc.), but not for molecules with-I-substituents (-CF3,-C (0) X,-N02,-CN, etc.). The correspondence between calculated and experimental results is improvedqualitatively when these densities are varied in accordance with a simple correction based on Slater’s rules. For those molecules for which the experimental trends are qualitatively reproduced, a sensitivity to substituent effects is predicted which is closerto the experimental results than what would be predicted by simple arguments based on carbon s character. ne of the most frequently studied classes of nuclear spin-spin coupling constants, and one which has appeared quitefrequently in qualitative theoretical arguments, is the directly bonded CH constant. Relatively straightforward experimental access via satellite experiments and intriguing early interpretations in terms of carbon hybridization generated a great deal of ex-perimental activity directed toward this nmr param-eter. 2-20 The early hybridization arguments were