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.
Key Takeaways: Anti-Periplanar Definition
- Anti-periplanar and syn-periplanar are a pair of terms used to describe chemical bond geometry of a molecule.
- The anti-periplanar conformation is a periplanar conformation in which the dihedral angle between two atoms or groups of atoms is between ±150° and 180°. In this conformation, the groups are anti-coplanar.
- The syn-periplanar conformation is a periplanar conformation in which the dihedral angle between the atoms or groups is between ±30°. In this conformation, both groups are on the same side of the 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.