text: The term anti-periplanar was first coined by Klyne and Prelog in their work entitled "Description of steric relationships across single bonds", published in 1960. ‘Anti’ refers to the two functional groups lying on opposite sides of the plane of the bond.  ‘Peri’ comes from the Greek word for ‘near’ and so periplanar means “approximately planar”. In their article “Periplanar or Coplanar?” Kane and Hersh point out that many organic textbooks use anti-periplanar to mean completely anti-planar, or anti-coplanar, which is technically incorrect.