Chem 240 Videos - Video 37
Updated (with better sound! Better production values! Chem3D images!) version is HERE: https://youtu.be/KxjjbX7Susc
The key orbital alignment in an E2 elimination is "anti-periplanar". The Leaving group is aligned with, but opposite the H that is abstracted. This is to ensure good overlap between C-H sigma and C-LG sigma star orbitals...
...but it also has implications for geometry and regioisomerism that are best illustrated in 6-membered ring systems or via newman projections, as illustrated.
