 Antiperiplanar conformation

An antiperiplanar conformation places two specified bonds in approximately the same plane with a dihedral angle of $180^{\circ }$. The designation concerns those particular bonds, not the planarity of the entire molecule.

In many E2 elimination reactions, the carbon-hydrogen bond being broken and the carbon-leaving-group bond align antiperiplanar. This arrangement supports the orbital overlap required to form the new pi bond. In a cyclohexane chair, the condition often requires a trans-diaxial pair, linking conformational geometry directly to which elimination pathway is accessible.