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Isomer types:

Compounds that have the same molecular formula but different chemical structures are called isomers.
Depending on what types of differences there are between the structures, it is possible to classify isomers into various sub-types.
If you "click" on the named boxes there is a link to a definition and an example.

Types of Isomer tree


Constitutional (or structural) isomers differ in the order in which the atoms are connected so they contain different functional groups and / or bonding patterns:

  • example: 1-propanol, 2-propanol and ethyl methyl ether (C3H8O)

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Stereoisomers contain the same functional groups and differ only in the arrangement of atoms in space.

Conformational isomers (or conformers or rotamers) are stereoisomers produced by rotation about sigma bonds, typically rapidly interconverting at room temperature:

  • example 1: butane : staggered (left) and eclipsed (center).The C2-C3 sigma bond rotation is animated (right). Try rotating the model to look along the C-C to see the two forms.

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  • example 2: cyclohexane : chair (left) and boat (right).These two forms can be interconverted by twisting the ring structure.

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Configurational isomers are stereoisomers that do not readily interconvert at room temperature and can (in principle at least) be separated.

Geometric isomers are configurational isomers that differ in the spatial position around a bond with restricted rotation (e.g. a double bond):

  • E-2-butene and Z-2-butene

Optical isomers are configurational isomers that differ in the 3D relationship of the substituents about one or more atoms:

Enantiomers are optical isomers that are non-superimposable mirror images.

  • (R)- or (S)-2-chlorobutane. Try moving the images to show that they are mirror images.

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Diastereomers are optical isomers that are not enantiomers.
  • (S,R)- or (R,R)-2-bromo-3-chlorobutane

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 © Dr. Ian Hunt, Department of Chemistry, University of Calgary

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