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
By
Anne Marie Helmenstine, Ph.D.
Anne Marie Helmenstine, Ph.D.
Chemistry Expert
  • Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
  • B.A., Physics and Mathematics, Hastings College
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
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Updated on November 05, 2019

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.

 

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Helmenstine, Anne Marie, Ph.D. "Anti-Periplanar Conformation Definition." ThoughtCo, Aug. 25, 2020, thoughtco.com/anti-periplanar-conformation-definition-603388. Helmenstine, Anne Marie, Ph.D. (2020, August 25). Anti-Periplanar Conformation Definition. Retrieved from https://www.thoughtco.com/anti-periplanar-conformation-definition-603388 Helmenstine, Anne Marie, Ph.D. "Anti-Periplanar Conformation Definition." ThoughtCo. https://www.thoughtco.com/anti-periplanar-conformation-definition-603388 (accessed April 19, 2024).