The $E2$ (Elimination Bimolecular) mechanism involves the concerted removal of a proton and a leaving group.

• Base: Requires a strong base ($Et{O}^{-},O{H}^{-},N{H}_2^{-}$) to abstract the $\beta$-proton.
• Geometry: The reaction requires Anti-periplanar geometry. The $C-H$ bond being broken and the $C-X$ bond being broken must be in the same plane but in opposite directions ($180^{\circ }$ dihedral angle).
• This minimizes electronic repulsion between the electron-rich base and the leaving group.