Diabatic surface methods for the study of the reactivity of organic molecules. 1. Cycloaddition of two ethylenes

In this paper we discuss the quantitative diabatic surface analysis of the surface associated with the thermal cycloaddition of two ethylene molecules. We show that the main features of a saddle point, such as the index (i.e., the number of negative eigenvalues of the Hessian) and the origin, can be understood by analyzing the behavior of the reactant and product diabatic surfaces computed in a three-dimensional subspace involving two relevant geometrical variables at a time. We show also that the behavior of the constituent diabatic surfaces can be easily rationalized with the simple energy expressions of qualitative MO theory. © 1986, American Chemical Society. All rights reserved.