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Structural isomerism

Structural isomerism, or constitutional isomerism, is a type of isomerism where isomers have the same molecular formula but have different arrangements of atoms within the molecule. e.g. n-pentane, isopentane and neopentane are structural isomers.

One of two or more compounds that contain the same number and kinds of atoms but that differ significantly in their geometric arrangement is to be considered as structural isomers.

Some common examples of Structural Isomers

  • Butane and isobutane (C4H10).
  • Pentan-1-ol, pentan-2-ol, and pentan-3-ol are structural isomers that exhibit position isomerism.
  • Cyclohexane and hex-1-ene are examples of functional group structural isomers.

Isomers that contain the same number of atoms of each kind but differ in the (bonding positions), positions at which atoms are bonded to one another are called structural isomers, which differ in structure or bond type. For inorganic complexes, there are three types of structural isomers: 

  • Ionisation
  • Coordination 
  • Linkage

The number of possible constitutional isomers increases greatly with the number of available atoms. There are only two butanes, but there are three pentanes (C5H12), 18 octanes (C8H18), and no fewer than 366,319 constitutional isomers of the hydrocarbon containing 20 carbon atoms and 42 hydrogens.

Types of Structural Isomerism

There are three types of structural isomerism:

  1. Chain isomerism.
  2. Functional group isomerism.
  3. Position isomerism.

Two main forms of isomerism

  1. Structural isomerism
  2. Stereo isomerism

Isomerism is classified into two main types that are structural or constitutional isomerism and stereoisomerism, in structural isomerism the bonds between the atoms differ; and stereoisomerism or spatial isomerism, the bonds are the same but the relative positions of the atoms differ.

Pentane Structural Isomerism

Pentane has three structural isomers. They are as follows:

N-pentane: The straight chain normal structure of Pentane is known as N-Pentane.

Iso-pentane: In this isomer of Pentane, one carbon atom is branched with the one carbon atom in the straight chain of the  other four carbon atoms. The IUPAC name of Iso-pentane is 2-methylbutane.

Neo-pentane: In this isomer of Pentane, two carbon atoms are branched with the central carbon atom in the straight chain of the other 3 carbon atoms. The IUPAC name of Neo-pentane is 2,2-dimethylpropane.

Conclusion 

In chemistry, a structural isomer of a compound is another compound whose molecule has the same number of atoms, but with logically different bonds between them. These are important because two isomers can have the same chemical formula, but have different chemical structures. The structure contributes to the properties of the molecule. In structural isomers, the atoms in each isomer are connected, or bonded, in different ways. As a result, structural isomers often contain different functional groups or patterns of bonding. Isomers will have different bonding properties and will form different disaccharides and macromolecules depending on the isomer involved, e.g. glucose and fructose are structural isomers; glucose + glucose forms maltose, glucose + fructose forms sucrose.