Suresh Cherumuttathu H, Alexander P, Vijayalakshmi K Periya, Sajith P K, Gadre Shridhar R
Computational Modeling and Simulation Section, National Institute for Interdisciplinary Science and Technology (CSIR), Trivandrum 695 019.
Phys Chem Chem Phys. 2008 Nov 21;10(43):6492-9. doi: 10.1039/b809561b. Epub 2008 Sep 24.
Density functional theory computations at the B3LYP/6-31G(d,p) level have been carried out for three types of model compounds, viz. (i) 4-substituted bicyclo[2.2.2]octane carboxylic acids, (ii) anions of 4-substituted bicyclo[2.2.2]octane carboxylic acids and (iii) 4-substituted quinuclidines where the substituents are NO(2), CN, Cl, Br, CF(3), F, CHO, CH(2)Cl, COOH, COCH(3), CONH(2), OH, OCH(3), C(6)H(5), NH(2), H, CH(3), CH(2)CH(3), CH(CH(3))(2), and C(CH(3))(3) to study the dependencies between molecular electrostatic potential minimum (V(min)) and the inductive substituent constant sigma(I). All the three model systems show excellent linear correlation between V(min) and sigma(I) suggesting that the calculation of V(min) parameter in these systems offers a simple and efficient computational approach for the evaluation of inductive substituent constants. The calculated linear equation for the models (i), (ii), and (iii) are V(min) = 12.982 sigma(I)- 48.867, V(min) = 13.444 sigma(I)- 182.760, and V(min) = 18.100 sigma(I)- 65.785, respectively. Considering the simplicity of the quinuclidine model, V(min) value at the nitrogen lone pair region of a 4-substituted quinuclidine system is recommended for the evaluation of sigma(I). Further, the additivity effect of sigma(I) is tested on multiply substituted quinuclidine and bicyclo[2.2.2]octane carboxylic acid derivatives using the V(min) approach and the results firmly supported the additivity rule of inductive effect. The systems showing considerable deviations from the additivity rule are easily recognized as those showing either steric effect or intramolecular hydrogen bond interactions at the V(min) response site. However, the distance relation of sigma(I) is not well represented in the caged molecular systems.
在B3LYP/6 - 31G(d,p)水平上对三种类型的模型化合物进行了密度泛函理论计算，即：(i) 4 - 取代双环[2.2.2]辛烷羧酸，(ii) 4 - 取代双环[2.2.2]辛烷羧酸的阴离子，以及(iii) 4 - 取代奎宁环，其中取代基为NO(2)、CN、Cl、Br、CF(3)、F、CHO、CH(2)Cl、COOH、COCH(3)、CONH(2)、OH、OCH(3)、C(6)H(5)、NH(2)、H、CH(3)、CH(2)CH(3)、CH(CH(3))(2)和C(CH(3))(3)，以研究分子静电势最小值(V(min))与诱导取代基常数sigma(I)之间的相关性。所有这三种模型体系均显示出V(min)与sigma(I)之间具有良好的线性相关性，这表明在这些体系中计算V(min)参数为评估诱导取代基常数提供了一种简单有效的计算方法。模型(i)、(ii)和(iii)的计算线性方程分别为V(min) = 12.982 sigma(I) - 48.867、V(min) = 13.444 sigma(I) - 182.760和V(min) = 18.100 sigma(I) - 65.785。考虑到奎宁环模型的简单性，建议使用4 - 取代奎宁环体系中氮孤对区域的V(min)值来评估sigma(I)。此外，使用V(min)方法对多取代奎宁环和双环[2.2.2]辛烷羧酸衍生物的sigma(I)加和效应进行了测试，结果有力地支持了诱导效应的加和规则。与加和规则有显著偏差的体系很容易被识别为在V(min)响应位点表现出空间效应或分子内氢键相互作用的体系。然而，sigma(I)的距离关系在笼状分子体系中并未得到很好的体现。
