Isomers

Isomers are molecules that have the same molecular formula, but have a different arrangement of the atoms in space. That excludes any different structures (isomers) which are simply due to the molecule rotating as a whole, or rotating about particular bonds. For example, both of the following are the same molecule. They are not isomers.

Types of Isomers

There are two main types of isomers. These are structural isomers and stereoisomers.

Structural Isomers

Structural isomers have the same molecular formula but the bonding connections or their order differs.

Chain Isomerism

Chain isomerism occurs among the alkanes. These are hydrocarbons with the formula CnH2n+2. The carbon atoms can be arranged in a chain in various ways.

Functional Group Isomerism

Functional group isomerism occurs when there are two or more possibilities for the functional group you can have.

Tautomeric Isomerism

Tautomeric isomerism is a special type of functional group isomerism and involves the simultaneous shift of a hydrogen atom and a double bond position.

Stereoisomers

Stereoisomers are isomers that differ in spatial arrangement of atoms, rather than order of atomic connectivity. One of their most interesting type of isomer is the mirror-image stereoisomers, a non-superimposable set of two molecules that are mirror image of one another. The two forms are called enantiomers.

See Also

• Enantiomers
• Structural isomer
• Stereoisomer
• Functional group isomerism
• Tautomeric isomerism

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