PMO Analysis of Cycloadditions, I Diels‐Alder Reactions of 2,3‐Bis(methylene)norbornane

A perturbational molecular orbital (PMO) treatment within the semiempirical MINDO/3 approximation is applied to the cycloadditions of 2,3‐bis(methylene)norbornane ( 1 ) to electron‐deficient olefins ( 2 – 5 ). Different contributions to the interaction energy deriving from steric effects, polar effects, and orbital interactions are analysed. The results, obtained by the program package PERVAL, which is developed for an IBM AT personal computer, are evaluated graphically. The origin of the reactivity sequence 2 < 3 < 4 < 5 is traced back to the HOMO diene ‐LUMO dienophile interaction. Various possibilities to interpret the results of PMO calculations are demonstrated.