JCE Software Chemistry Comes Alive!
Diels-Alder Visualization - Part 3 of 3

An animation of hybrid orbitals changing shape is presented as a simpler way to visualize the reaction.

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Narrative
It is more informative and less arbitrary to replace the three filled molecular orbitals by the six half-filled hybrid orbitals of which they are composed. Now there is no need to represent the bonds as shifting in a clockwise or counterclockwise direction.

Each hybrid merely changes its shape from pure p to sp3 and reorients slightly to overlap with a different hybrid in the new bonding pattern. Note how little real change in hybrid shape and orientation is needed in order to accomplish this three bond transformation.

Visualizing orbital interactions between molecules can explain why some chemical reactions can occur easily and others don't.