Periplanar refers to two atoms or groups of atoms in a conformation are in the same plane with respect to the reference single bond.
The image shows two conformations of butane (C4H10). The methyl groups (-CH3) are lined up in the same plane with the middle carbon-carbon single bond.
The top conformation is known as syn-periplanar and the bottom is known as anti-periplanar.
Sources
- March, Jerry (1985). Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.). New York: Wiley. ISBN 0-471-85472-7.
- Testa, Bernard; Caldwell, John (2014). Organic Stereochemistry: Guiding Principles and Biomedicinal Relevance. ISBN 390639069.