Anti-Periplanar Conformation Definition

Definition of Anti-Periplanar Conformation

Butane Anti-periplanar Conformation
This shows butane in the anti-periplanar conformation in sawhorse and Newman projections. Todd Helmenstine

Two of the terms you may encounter in organic chemistry are anti-periplanar and syn-periplanar. Both refer to the geometry of chemical bonds in a molecule.

Anti-Periplanar Definition

Anti-periplanar refers to a periplanar conformation where the dihedral angle between two atoms or groups of atoms is  between ±150° and 180°. In texts, anti-periplanar means bonds are anti-coplanar.

The image shows butane (C4H10) in a syn-periplanar conformation where the two methyl groups (-CH3) are lined up with a 180° angle.

Syn-coplanar is related to anti-periplanar. The dihedral angle between the atoms or groups is between ±30° and the groups are both on the same side of the plane as each other.

Sources

  • Eliel, Ernest; Wilen, Samuel; Mander, Lewis (September 1994). Stereochemistry of Organic Compounds. New York: Wiley-Scientific.
  • Kane, Saul; Hersh, William (1 October 2000). "Periplanar or Coplanar?". Journal of Chemical Education. 77 (10): 1366.