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Ring - Chain Isomerism | Structural isomerism

Learning Objective: To learn about ring–chain isomerism, a subtype of structural isomerism. 

Skill Level – Intermediate

 

Prerequisites: 

Related – 

 

Chapter: Structural Isomerism

 

Author's Note: Ring-chain isomerism demonstrates two forms of representing an organic compound that can exist as a flexible open chain or rigid close structure. This difference leads to various possibilities –

-  Certain drugs or natural compounds may exhibit different effects depending on whether they are in an open-chain or ring form.

- Open-chain compounds may be more reactive in specific reactions than their ring counterparts, which can be more stable.

- The physical properties of ring-chain isomers, such as boiling points, melting points, and solubility, can differ significantly, affecting separation techniques.

Therefore, it is essential to study how to identify two ring-chain isomers and predict their structural formula. This section details ring-chain isomerism, its examples, functional groups commonly exhibiting ring-chain isomerism, and more.

Ring - Chain Isomerism 

Compounds may have the same molecular formula but can vary in their structures such that they can exist in open chain or closed are called ring-chain isomers, and the phenomenon is called ring-chain isomerism.

The compounds must have at least a DBE value of 1 to show ring and chain isomerism.

For example, 

 

a) Alkenes and cycloalkanes (CnH2n)

An example of CnH2n is C3H6, a molecular formula that has one degree of unsaturation in this structure. 

One degree of unsaturation (*DBE) can be one double bond or a cyclic ring. Therefore, the ring-chain isomer of C3H6 is-

 

 

C4H8 represents-

 

 

b) Alkynes and cycloalkenes (CnH2n-2)

An example of CnH2n-2 is ....

 

c) Unsaturated alcohols and cyclic ethers (CnH2nO)

Molecules with the general molecular formula CnH2nO have....

 

 

Subscribe to learn all subtypes of structural isomerism.

Structural Isomerism
Organic Chemistry - Drawing Structures, Concepts, and Examples

Sibi Atul

Author Bio

Sibi Atul holds an M.Sc. in Drug Chemistry and spent several years as a Research Scientist in medicinal chemistry before moving into undergraduate teaching. She now writes and edits full-time at CurlyArrows — an organic chemistry platform trusted by learners in over 170 countries for more than 11 years — where she has authored hundreds of illustrated tutorials, Q&As, and course modules. She also hosts the podcast Learning Organic Chemistry with Sibi. Her drug discovery background and classroom experience uniquely qualify her to make complex chemistry accessible to students worldwide. Connect with Sibi on LinkedIn

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Structural Isomerism

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Reactive Intermediates

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Stereoisomerism - Conformation and Configurational Isomerism

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