Constitutional isomer

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Constitutional isomers, also known as structural isomers[1], are isomers that share the same molecular formula but has different structural formula or different order of attachment of atoms[2]. There are 3 types of constitutional isomers, which are functional group isomers, chain isomers and position isomers.

Functional group isomers are isomers containing varied functional groups. Butane and methylpropane are examples of functional group isomerism.

Chain isomers have different length of carbon chains despite the equal number of each atoms. For example, butane and 2-methylpropane show chain isomerism.

Every position isomers show different positions of their functional groups respectively. For example, 1,2-dibromopropane and 1,3-dibromopropane exist as position isomers[3].

However, some molecular formulas do not exhibit constitutional isomerism because there is only one way of connecting the atoms within the compound. Examples include methane, ethane and propane[4].


  1. Bettelheim FA, Brown WH, Campbell MK, Farrell SO. Introduction to Organic and Biochemistry Seventh Edition. 2010. Brooks/Cole. Belmont. Pg 20
  2. Burg J M, Tymoczko J L, Gatto, Jr G J, Stryer L. Biochemistry Eighth Edition. 2015. W.H. Freeman and Company. New York. Pg 317
  3. Ryan L, Norris R. Cambridge International AS and A Level Chemistry Coursebook Second Edition. 2014. Latimer Trend. UK. Pg 194 - 195
  4. Bettelheim F, Brown W, Campbell M, Farrell S. Introduction to General, Organic and Biochemistry Eighth Edition. 2007. Thomson Brooks/Cole. Belmont. Pg 305
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