In chemistry,<unk>  is a form of stereoisomerism involving the phenomenon of molecules with the same structural formula existing as different<unk>  isomers or conformers due to atoms rotating about a bond.
There are three principle effects that make some conformers more stable than others:
File:Conformers01.jpgDifferent conformers can interconvert by rotation around single bonds, without breaking chemical bonds. A simplified example is that of a butane molecule viewed in the Newman projection shown - i.e. as if viewed down the central C-C bond with relative rotations of C² and C³ illustrated. Rotamers are a set of conformers and the rotation barrier is the activation energy required to jump from one conformer to another conformer.
The population of different conformers follows a Boltzmann distribution:
The subscripts i and j represent the highest and lowest energy. g is the number of conformations found at that particular energy, the degeneracy. N is the population of molecules in a particular conformation.
Two important forms of<unk>  exist:
Another example of<unk>  is the folding of molecules, where some shapes are stable and functional, but others are not.<unk>  is also found in atropisomers.
Conformational isomerism
Cis-trans isomerism
Equilibrium unfolding
Thermal depolymerization
Mutualism
Exothermic reaction
Dislocations
Chemical modification