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(of molecules), geometric forms that molecules of organic compounds can assume during the rotation of atoms or groups of atoms (substituents) about single bonds while maintaining the order of the chemical bonding of the atoms (chemical structures), the bond lengths, and valency angles. Molecules that differ from one another only in conformation are called conformers, or rotational isomers. The existence of conformations is determined by the spatial interaction (such as repulsion, attraction, and hydrogen bond formation) of substituents (hydrogen atoms included) that are not bonded to one another. One such example (see Figure 1) is represented by several planar conformations of a pentane molecule:
Unlike geometric and optical isomers, conformers under general conditions easily convert into one another (without the breaking of bonds) and therefore cannot be isolated (compareCONFIGURATION). The molecules of organic compounds usually exist in the form of a mixture of conformers that are in equilibrium,
among which those that are energetically most favorable, that is, exhibiting the lowest energy, predominate. The conformational state of molecules affects the physical properties of substances and the orientation and rate of chemical transformations (see).
V. M. POTAPOV