Conformational isomerism is the phenomenon of molecules with the same structural formula but different conformations (conformers) of atoms about a rotating bond. Steric repulsion will make some conformers more favourable than others - i.e. they will have a lower energy level. 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. In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of bonds between atoms, but in which the atoms are arranged differently. ... Jump to: navigation, search A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... Many chemical compounds, especially hydrocarbons, can exist in different geometric configurations. ... In chemistry, a chemical conformation is the spatial arrangement of atoms in a molecule. ... Jump to: navigation, search Properties For alternative meanings see atom (disambiguation). ... A chemical bond is the phenomenon of atoms being held together in molecules or crystals. ... Steric effects are the interaction of molecules dictated by their shape and/or spatial relationships. ... Butane, also called n-butane, is the unbranched alkane with four carbon atoms, CH3CH2CH2CH3. ...

Potential energies (of butane)

A measure of potential energy is stored in conformers with greater steric hindrance than the 'anti' conformer ground state. Jump to: navigation, search Potential energy is stored energy. ...

• Staggered a.k.a. gauche conformer - 16 kJ/mol
• Eclipsed H and CH₃ - 3.8 kJ/mol
• Eclipsed CH₃ and CH₃ - 19 kJ/mol

The eclipsed methyl groups exert a greater steric strain because of their greater electron density compared to lone hydrogen atoms. In chemistry a staggered conformation is a chemical conformation that exists in any open chain single chemical bond connecting two sp3 hybridised atoms as a conformational energy minimum. ... In chemistry an eclipsed conformation is a chemical conformation that exists in any open chain single chemical bond connecting two sp3 hybridised atoms as a conformational energy maximum due to steric hindrance. ... In chemistry a methyl-group is a hydrophobic Alkyl functional group which is derived from methane (CH4). ... Electron density is the measure of the probability of an electron being present at a specific location. ... Jump to: navigation, search General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...

Consequences

If the eclipsed conformations of an isomer have high enough potentials, they may prevent rotation of substituents to different staggered conformations at sufficiently low energy levels. This will result in a racemic mixture of conformations that may or may not have different reactivities in situations such as enzymatic reactions in which molecular shape is usually a key factor of operation. In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of bonds between atoms, but in which the atoms are arranged differently. ... In organic chemistry, a substituent is an atom or group of atoms subsituted in place of a hydrogen atom on the parent chain of a hydrocarbon. ... In chemistry, a racemate is a mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecule. ... Reactivity refers to the rate at which a chemical substance tends to undergo a chemical reaction in time. ... Jump to: navigation, search Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ...

Conformer dependent reactions

The E2 elimination mechanism relies on the base or acid attacked substituent being in an antiperiplanar configuration along a bond with respect to the leaving group. This prerequisite for reaction is important in understanding organic elimination reaction pathways, especially those involving halogenated cyclic alkanes. Two adjacent substituents on a cyclic alkane can only undergo an E2 elimination if they are both axial to the ring and hence antiperiplanar. A combination of axial and equatorial substituents cannot react through an E2 mechanism, though ring flips (with associated reconformation) may allow reactions to occur if they are not precluded by an energy barrier or steric lock through isopropyl or larger substituents. An elimination reaction is a type of organic chemical reaction in which two groups are removed from a molecule in either a one or two-step mechanism. ... A leaving group is an atom or molecule that detaches from an organic molecule, which, after detachment, is called the residual or main part. ...

Conditions

Conformational isomerism only occurs around single bonds as a result of the requirement of breaking one or more pi bonds to rotate substituents about a sigma bond axis in double and triple bonded atoms. Conformers sufficiently constrained to exhibit measurable isomerism are unique from various flavours of stereoisomers in the fact that changes in stereochemistry are independent from any mechanism and instead rely only on molecular energy. Electron atomic and molecular orbitals, showing a Pi-bond at the bottom right of the picture In chemistry, pi bonds (π bonds) are bonds with a single nodal plane containing the line segment between the two atoms. ... In organic chemistry, a substituent is an atom or group of atoms subsituted in place of a hydrogen atom on the parent chain of a hydrocarbon. ... Electron atomic and molecular orbitals, showing among others the sigma bond of two s-orbitals and a sigma bond of two p-orbitals In chemistry, sigma bonds (σ-bonds) are bonds where there is no nodal plane containing the line segment between the two bonded species. ...

See also

• isomer
  • diastereomer
  • enantiomer
  • chirality
• Steric effects
• Chemical conformation
  • Chair conformation
  • Cyclohexane