text: Rotating their carbon–carbon bonds, the molecules ethane and propane have three local energy minima.  They are structurally and energetically equivalent, and are called the staggered conformers.  For each molecule, the three substituents emanating from each carbon–carbon bond are staggered, with each H–C–C–H dihedral angle (and H–C–C–CH dihedral angle in the case of propane) equal to 60° (or approximately equal to 60° in the case of propane).  The three eclipsed conformations, in which the dihedral angles are zero, are transition states (energy maxima) connecting two equivalent energy minima, the staggered conformers.
  The butane molecule is the simplest molecule for which single bond rotations result in two types of nonequivalent structures, known as the anti- and gauche-conformers (see figure).
  For example, butane has three conformers relating to its two methyl (CH) groups: two gauche conformers, which have the methyls ±60° apart and are enantiomeric, and an anti conformer, where the four carbon centres are coplanar and the substituents are 180° apart (refer to free energy diagram of butane). The energy difference between gauche and anti is 0.9 kcal/mol associated with the strain energy of the gauche conformer. The anti conformer is, therefore, the most stable (≈ 0 kcal/mol). The three eclipsed conformations with dihedral angles of 0°, 120°, and 240° are transition states between conformers. Note that the two eclipsed conformations have different energies: at 0° the two methyl groups are eclipsed, resulting in higher energy (≈ 5 kcal/mol) than at 120°, where the methyl groups are eclipsed with hydrogens (≈ 3.5 kcal/mol).
  While simple molecules can be described by these types of conformations, more complex molecules require the use of the Klyne–Prelog system to describe the different conformers.
  More specific examples of conformational isomerism are detailed elsewhere:
  *Ring conformation
  **Cyclohexane conformations, including with chair and boat conformations among others.
  **Cycloalkane conformations, including medium rings and macrocycles
  **Carbohydrate conformation, which includes cyclohexane conformations as well as other details.
  *Allylic strain – energetics related to rotation about the single bond between an sp carbon and an sp carbon.
  *Atropisomerism – due to restricted rotation about a bond.
  *Folding, including the secondary and tertiary structure of biopolymers (nucleic acids and proteins).
  *Akamptisomerism – due to restricted inversion of a bond angle.