text: Many definitions that describe a specific conformer (IUPAC Gold Book) exist, developed by William Klyne and Vladimir Prelog, constituting their Klyne–Prelog system of nomenclature:
  * a torsion angle of ±60° is called gauche
  * a torsion angle between 0° and ±90° is called syn  (s)
  * a torsion angle between ±90° and 180° is called anti (a)
  * a torsion angle between 30° and 150° or between –30° and –150° is called clinal
  * a torsion angle between 0° and 30° or 150° and 180° is called periplanar (p)
  * a torsion angle between 0° to 30° is called synperiplanar or syn- or cis-conformation (sp)
  * a torsion angle between 30° to 90° and –30° to –90° is called synclinal or gauche or skew (sc)
  * a torsion angle between 90° to 150°, and –90° to –150° is called  anticlinal (ac)
  * a torsion angle between ±150° to 180° is called  antiperiplanar or anti or trans (ap).
  Torsional strain results from resistance to twisting about a bond.