https://doi.org/10.1351/goldbook.12187
Rotamer defined by a relative rotation about a skeletal bond of a single-strand chain.
Notes:
- A rotational isomeric state is conventionally defined over a sequence of three contiguous skeletal bonds with reference to the dihedral (or torsion) angle (\(\phi\)) between the planes defined by the first two bonds and the second two bonds. For example, for a chain composed of single \(\ce{C-C}\) skeletal bonds, \(\phi \approx 0^{\circ}\) can be used to define the (planar) trans (\(t\)) rotational isomeric state, and \(\phi \approx \pm 120^{\circ}\) to define the gauche\(\pm\) (\(g_{\pm}\)) rotational isomeric states.
- Alternative notations exist. For example, \(\phi = 180°, \pm 60^{\circ}\), respectively, can be used to denote the \(t\) and \(g_{\pm}\) states, which can also be given the symbols \(\rm{T}\), \(\rm{G}^{+}\), and \(\rm{G}^{-}\). The trans and gauche states or conformers are also known as the "antiperiplanar conformers" and "synclinal conformers". The notation used in Note 1 is that introduced by Flory and co-workers and is now the one most frequently used in polymer science.
- The energies of rotational isomeric states are determined by short-range intramolecular interactions.