Anti-periplanar

In organic chemistry, anti-periplanar, or antiperiplanar, describes the A−B−C−D bond angle in a molecule. In this conformer, the dihedral angle of the A−B bond and the C−D bond is greater than +150° or less than −150°[1] (Figures 1 and 2). Anti-periplanar is often used in textbooks to mean strictly anti-coplanar,[2] with an A−B C−D dihedral angle of 180° (Figure 3). In a Newman projection, the molecule will be in a staggered arrangement with the anti-periplanar functional groups pointing up and down, 180° away from each other (see Figure 4). Figure 5 shows 2-chloro-2,3-dimethylbutane in a sawhorse projection with chlorine and a hydrogen anti-periplanar to each other.

Syn-periplanar or synperiplanar is similar to anti-periplanar. In the syn-periplanar conformer, the A and D are on the same side of the plane of the bond, with the dihedral angle of A−B and C−D between +30° and −30° (see Figure 2).

Figure 1: Functional groups A and D are anti-periplanar
Figure 2: Functional groups are considered periplanar if they have a dihedral angle less than −150° or greater than +150° or −30° to +30°. Adapted from a figure by Dreamtheater published on Wikimedia Commons.[3]
Figure 3: Representation of a strictly anti-coplanar conformation. A, B, C, and D are in the same plane and the dihedral angle between A–B and C–D is 180°.
Figure 4: Newman projection showing A and D anti-periplanar.
Figure 5: Sawhorse projection of 2-chloro-2,3-dimethylbutane showing Cl and H anti-periplanar.
  1. ^ Eliel, Ernest; Wilen, Samuel; Mander, Lewis (September 1994). Stereochemistry of Organic Compounds. New York: Wiley-Scientific. ISBN 978-0-471-01670-0.
  2. ^ Kane, Saul; Hersh, William (1 October 2000). "Periplanar or Coplanar?". Journal of Chemical Education. 77 (10): 1366. Bibcode:2000JChEd..77.1366K. doi:10.1021/ed077p1366.
  3. ^ Wikipedia, Dreamtheater at English (9 August 2012), English: An illustration of the syn/anti peri/clinal nomenclature of molecular torsional conformations. To be used on the page Alkane stereochemistry., retrieved 17 March 2017