Conformational isomerism

Conformational isomerism is the existence of distinct spatial arrangements of a molecule produced by rotation around single bonds, without breaking covalent bonds.

Conformer: A conformer is one of the spatial arrangements accessible to a molecule through rotation around single bonds. Each distinct arrangement produced by bond rotation is a conformer.
Single bond: A single bond is a covalent bond formed by one shared pair of electrons. Rotation around a single bond is the usual source of conformational change.
Ethane: Ethane is a two-carbon alkane with formula C₂H₆ and a freely rotating carbon–carbon single bond. Its staggered and eclipsed conformations provide the simplest model of torsional effects.
Boltzmann distribution: The Boltzmann distribution gives the relative populations of states at thermal equilibrium according to their energies and temperature. It predicts how strongly each conformer contributes to a molecular sample.
Configurational isomerism: Configurational isomerism describes stereoisomers that cannot interconvert without breaking and reforming covalent bonds. Unlike conformers, configurational isomers do not interconvert through ordinary single-bond rotation.
Torsional strain: Torsional strain is the energy increase caused by repulsion between bonding electron pairs in eclipsed or nearly eclipsed bonds. It makes eclipsed arrangements less stable than staggered ones.
Tetrahedral molecular geometry: Tetrahedral molecular geometry places four bonded groups around a central atom at angles near 109.5 degrees. Its three-dimensional geometry gives rotations around carbon bonds distinct spatial outcomes.
Butane: Butane is a four-carbon alkane whose central carbon–carbon bond connects two methyl groups. Rotation about its central bond yields anti and gauche conformers with different energies.
Nuclear magnetic resonance spectroscopy: Nuclear magnetic resonance spectroscopy studies atomic nuclei in magnetic fields using their responses to radiofrequency radiation. Its signals can reveal conformational populations and exchange rates.
Cis–trans isomerism: Cis–trans isomerism distinguishes arrangements in which substituents lie on the same or opposite sides of a reference plane or bond. Double-bond cis–trans forms require a different mechanism of interconversion than ordinary conformers.

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