Figure 4. HOMO-LUMO interaction in the Diels-Alder reaction

From

Using Balloons to Model Pi-Conjugated Systems and to Teach Frontier Molecular Orbital Theory

Daniel J. Swartling, Janet G. Coonce, Derek J. Cashman

World Journal of Chemical Education. 2018, 6(2), 102-106 doi:10.12691/wjce-6-2-5