Diels-Alder reaction: A theoretical comprehensive study of substituent effects using the 'H* method'

In a second part, we define and calculate indices of reactivity, which characterize the effects of a second substitution in a given position of monosubstituted ethylene or diene. We briefly discuss their consequences for reactivity, regioselectivity and stereoselectivity. Finally, we investigate the possibility of computing a partition of σ and π effects. We conclude that for butadiene substitution, σ effects are almost the same in positions 1 and 2 whereas π effects should be stronger in position 2.