Geometry: Anti-Periplanar
Reaction Coordinate Diagram

Concept Quiz

The E2 Mechanism

The E2 (Elimination Bimolecular) reaction is a concerted, single-step process. A strong base abstracts a proton from the $\beta$-carbon at the exact same time the leaving group departs from the $\alpha$-carbon, forming a double bond.

Rate $= k [\text{Substrate}][\text{Base}]$
Stereospecificity (Anti-Periplanar):
For the new $\pi$ bond to form smoothly, the developing $p$-orbitals must be parallel. This geometrically requires the leaving group and the $\beta$-proton to be strictly $180^\circ$ apart (anti-periplanar) in the transition state.