Abstract
The Diels-Alder reactions may be the most important class of organic reactions. There reactions have high regio- and stereo-selectivity. In this study, we have studied the reaction mechanisms between 1,1-substituted ethylene and butadiene. As substituent groups of 1,1-substituted, electron donor group (CH3, C2H5, OH, OCH3, NH2) and electron attractive groups (F, Cl, CN, CHO, NO2) are chosen. All equilibrium and transition state structures were determined with analytically calculated energy gradients at the CASSCF method with 6-31G(d) basis set. To interpret the mechanism of the concerted pathway, CiLC analysis was performed along the IRC pathway. The reactions between butadiene and substituted ethylene with electron donor groups have lager activation energy barriers than these with electron attractive groups. Generally, F and Cl substitution groups are classified into electron attractive groups. But, these substitution groups look like electron donor groups from the activation energy barriers. Accordingly, the electronic state of substituted ethylene was characterized by using the CiLC method. This analysis implies that F, Cl have electron donating ability under Diels-Alder reactions. From above result, we revealed a correlation that the class of the substituted ethylene on the basis of the CiLC analysis might adopt either the concerted or stepwise reaction pathways.
