Final answer:
In E2 reactions, anti and syn coplanar refer to the relative positions of the hydrogen and leaving group atoms on the reactant molecule.
Step-by-step explanation:
In E2 reactions, anti and syn coplanar refer to the relative positions of the hydrogen and leaving group atoms on the reactant molecule.
Anti coplanar means that the hydrogen and leaving group are on opposite sides of the molecule's plane, while syn coplanar means they are on the same side of the plane.
The E2 mechanism occurs when these hydrogen and leaving group atoms are in the anti or syn coplanar positions, allowing for the concerted transfer of electron pairs and the formation of a double bond.