Types, Structures, Reactions, Uses and Properties of Isomers

Types, Structures, Reactions, Uses and Properties of Isomers


  • Isomers are compounds with the same molecular formula but different structural formulas.
  • They can have different physical and chemical properties due to the different ways their atoms are arranged.
  • The study of isomers sheds light on the versatility and dynamic nature of organic molecules.

Types of Isomers

  • There are two main types of isomers: structural (or constitutional) isomers and stereoisomers.
  • Structural isomers have the same molecular formula but a different connectivity of atoms. Sub-categories include chain isomers, functional group isomers, and tautomers.
  • Stereoisomers have the same molecular formula and sequence of bonded atoms but a different orientation in space. This class includes geometrical isomers and optical isomers.

Structures of Isomers

  • The structure of chain isomers varies by the arrangement of the carbon chain.
  • Functional group isomers contain different functional groups, for instance, aldehydes vs ketones and alcohols vs ethers.
  • Geometric isomers, a type of stereoisomer, differ in the position of substituents around a double bond.
  • Optical isomers are non-superimposable mirror images, similar to left and right hands, due to the presence of a chiral centre.

Reactions of Isomers

  • Structural isomers often show different chemical reactions, as their functional groups can be different.
  • Stereoisomers behave differently in reactions that are sensitive to the three-dimensional arrangement of atoms, such as with enzymes or other chiral molecules.

Uses of Isomers

  • Isomers have important applications in many areas, from fuels to pharmacology.
  • For instance, positional isomers of pentanol are used as solvents and in the manufacture of perfumes or artificial flavourings.
  • In medicine, different isomers of a drug can have drastically different levels of activity. The infamous drug thalidomide is a cautionary tale of chirality, with one isomer being therapeutic and the other being teratogenic.

Properties of Isomers

  • Physical properties of isomers, such as boiling point, melting point, and solubility, often differ due to differences in intermolecular forces.
  • For instance, straight-chain isomers have higher boiling points than their branched counterparts due to increased surface contact and hence stronger van der Waals forces.
  • Optical isomers rotate plane-polarized light in opposite directions, rendering them optically active, a characteristic property exploited in stereospecific syntheses.

Understanding the structures, reactions, uses and properties of isomers is imperative in the study of organics. The topic forms a linchpin for many advanced concepts, shedding light on the intricate nature of organic compounds.