In organic chemistry, anti-periplanar, or antiperiplanar, describes the  bond angle in a molecule. In this conformer, the dihedral angle of the  bond and the  bond is greater than +150° or less than −150° (Figures 1 and ). Anti-periplanar is often used in textbooks to mean strictly anti-coplanar, with an   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  and  between +30° and −30° (see Figure 2).