Diels Alder Regiochemistry

The regioselectivity of Diels-Alder reactions can be predicted by analyzing the electronic distribution in the reactants. The animation uses resonance structures and electrostatic potential maps to visualize these electronic effects.

1. The resonance hybrid of the electron-rich diene has partial negative charge concentrated at one end, as indicated by the electrostatic surface (red = electron-rich).
2. The resonance hybrid of the electron-poor dienophile has partial positive charge localized at one end (blue-green = electron-poor).
3. The reactants align their partial positive and negative charges, leading to the orientation that produces the major regioisomer.
4. In the transition state, concerted cyclic electron flow occurs to form the new bonds.