Acocella Angela, Marforio Tainah D, Calvaresi Matteo, Bottoni Andrea, Zerbetto Francesco
Department of Chemistry "G. Ciamician", Alma Mater Studiorum - University of Bologna, via Selmi 2, Bologna 40126, Italy.
J Chem Theory Comput. 2020 Apr 14;16(4):2172-2180. doi: 10.1021/acs.jctc.9b00690. Epub 2020 Mar 6.
The prototype Diels-Alder (DA) reaction between butadiene and ethene (system ) and the DA reaction involving 1-methoxy-butadiene and cyano-ethylene (system ) are investigated with an explicit-time-dependent Density Functional Theory approach. Bond orders and atomic net charges obtained in the dynamics at the transition state geometry and along the reaction coordinate toward reactants are used to provide a picture of the process in terms of VB/Lewis resonance structures that contribute to a resonance hybrid. The entire dynamics can be divided into different domains (reactant-like, product-like, and transition state domains) where different Lewis resonance structures contribute with different weights. The relative importance of these three domains varies along the reaction coordinate. In addition to the usual reactant-like and product-like covalent Lewis structures, ionic Lewis structures have non-negligible weights. In system , the electron-donor OCH on the diene and the electron-acceptor CN on the dienophile make more important the contributions of ionic Lewis structures that stabilize the transition state and determine the decrease of the reaction barrier with respect to system .
采用显式含时密度泛函理论方法研究了丁二烯与乙烯（体系 ）之间的原型狄尔斯-阿尔德（DA）反应以及涉及1-甲氧基-丁二烯和氰基乙烯（体系 ）的DA反应。在过渡态几何结构以及沿着朝向反应物的反应坐标的动力学过程中获得的键级和原子净电荷，用于根据对共振杂化体有贡献的VB/路易斯共振结构来描绘该过程。整个动力学过程可分为不同的区域（反应物类、产物类和过渡态区域），不同的路易斯共振结构在这些区域中以不同的权重起作用。这三个区域的相对重要性沿反应坐标而变化。除了通常的反应物类和产物类共价路易斯结构外，离子路易斯结构的权重也不可忽略。在体系 中，二烯上的给电子基团OCH和亲双烯体上的吸电子基团CN使得离子路易斯结构的贡献更为重要，这些离子路易斯结构稳定了过渡态，并决定了相对于体系 反应势垒的降低。
