Rotamer

In chemistry, rotamers are chemical species that differ from one another primarily due to rotations about one or more single bonds. Various arrangements of atoms in a molecule that differ by rotation about single bonds can also be referred to as different conformations. Conformers/rotamers differ little in their energies, so they are almost never separable in a practical sense.^{[citation needed]} Rotations about single bonds are subject to small energy barriers.^{[1][failed verification]} When the time scale for interconversion is long enough for isolation of individual rotamers (usually arbitrarily defined as a half-life of interconversion of 1000 seconds or longer), the species are termed atropisomers (see: atropisomerism).^[2][3][4] The ring-flip of substituted cyclohexanes constitutes a common form of conformers.^[5]

The study of the energetics of bond rotation is referred to as conformational analysis.^[6] In some cases, conformational analysis can be used to predict and explain product selectivity, mechanisms, and rates of reactions.^[7] Conformational analysis also plays an important role in rational, structure-based drug design.