Open AccessElectron Dynamics with Explicit-Time Density Functional Theory of the [4+2] Diels–Alder Reaction
Author(s) -
Angela Acocella,
Tainah Dorina Marforio,
Matteo Calvaresi,
Andreà Bottoni,
Francesco Zerbetto
Publication year - 2020
Publication title -
journal of chemical theory and computation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.001
H-Index - 185
eISSN - 1549-9626
pISSN - 1549-9618
DOI - 10.1021/acs.jctc.9b00690
Subject(s) - reaction coordinate , chemistry , resonance (particle physics) , density functional theory , ionic bonding , diels–alder reaction , reaction dynamics , lewis acids and bases , transition state , computational chemistry , covalent bond , chemical physics , diene , molecule , atomic physics , physics , catalysis , organic chemistry , ion , natural rubber
The prototype Diels-Alder (DA) reaction between butadiene and ethene (system 1 ) and the DA reaction involving 1-methoxy-butadiene and cyano-ethylene (system 2 ) 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 2 , the electron-donor OCH 3 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 1 .