Isomerism

Isomerism is one of the most important complexities of organic chemistry. The isomerism of molecules puzzled chemists for many years and remained unresolved until the mid-19th century.

General Map of Isomerism

Isomerism map: structural or constitutional isomers and stereoisomers, which can be conformers or configurational isomers (diastereomers and enantiomers)

Video: Functional isomerism: ethanol and dimethyl ether

Structural or constitutional isomers: different bond pattern (C₄H₁₀, C₂H₆O, C₆H₁₂)

A given molecular formula can correspond to a number of different compounds. Isomerism can affect the carbon chain, the functional group or both at the same time. The more atoms in the molecular formula, the greater the possibilities of isomerism. For instance, the molecular formula C₂₀H₄₂ corresponds to more than 200,000 different compounds, believe it or not...

Even with the same bond pattern, a molecular formula can represent several isomers that differ in the SPATIAL ARRANGEMENT of their atoms.

Isomers with the same bond pattern are stereoisomers

Video: Conformations: single bonds rotate

Conformers or rotamers: stereoisomers interconvertible by bond rotation (anti and gauche butane; equatorial and axial methylcyclohexane)

An important property of single bonds is that they can rotate, giving rise to structures with different spatial arrangements of their atoms. These subtle isomers are called ROTAMERS or CONFORMERS. Obviously, they interconvert by rotation about single bonds.

Isomers that have the same bond pattern but do not interconvert by rotation about single bonds are called CONFIGURATIONAL ISOMERS. Those that are not related as object and non-superimposable mirror image are called DIASTEREOMERS.

CONFIGURATIONAL ISOMERS that are related as object and non-superimposable mirror image are called ENANTIOMERS.

Configurational isomers: diastereomers (cis/trans) and enantiomers (R- and S-limonene)