Science, Tech, Math › Science Anti-Periplanar Conformation Definition Definition of Anti-Periplanar Conformation Share Flipboard Email Print This shows butane in the anti-periplanar conformation in sawhorse and Newman projections. Todd Helmenstine Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By 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. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated 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.