Learning Objective: To learn what is structural isomerism and its subtypes.
Skill Level – Intermediate
Chapter: Structural Isomerism
Author's Note: Structural isomerism is an important concept in organic chemistry that teaches structural variations within a molecule that contains the same number of atoms in the exact whole number ratio.
Such an analysis is crucial since one isomer may be more useful than the other. For example, in the petroleum industry, isooctane, an isomer of n-octane has greater capability to lower the knocking for smoother engine functionality. Similarly, while both butane and isobutane are C4H10, their structural arrangement attributes fuel-like properties to butane, whereas isobutane is a refrigerant and propellant in aerosol sprays.
While each isomer shares a similar set of atoms, they are dissimilar in their physical and chemical properties due to the variation in their structural arrangements.
Structural Isomerism - Introduction and Subtypes
Imagine you are in a MasterChef competition, and it is a Mystery Box Challenge. You must create a unique recipe using only a fixed number of ingredients. Each person in the competition will have their unique signature version. In such a situation where the number of ingredients is fixed, the variety, and the unique recipes it produces, play a crucial role.
Similarly, in the realm of chemistry, the concept of structural isomerism is like a culinary Mystery Box Challenge. Molecules, like chefs, craft unique structures, each with its own distinct attachments from a fixed number of atoms. This individuality is what makes the concept of structural isomerism so intriguing.
Just as each recipe in a cooking competition has its own unique taste, each structure in structural isomerism has its own unique physical and chemical properties. This variety and distinctiveness are what make the concept of structural isomerism fascinating.
For example, different ways to represent carbon-hydrogen-containing hydrocarbons having a fixed number of atoms are shown below.
In all the above structures, what changed was how the atoms connected differently when the carbon count increased to four and five to form dissimilar molecules, revealing their structural diversity.
As you can see, with the increase in the number of carbon atoms, the number of variations or the structural isomers also increases.
To explain more elaborately, one, two, three carbon methane, ethane, and propane have no isomers; four-carbon butane has 2 isomers; five-carbon pentane has 3 isomers; six-carbon hexane has 5 isomers; seven-carbon heptane has 9 isomers, eight-carbon octane has 18 isomers; ten-carbon decane has 75 isomers, and so on.
The increase in the number of isomers is not linear. Also, complexity arises when a heteroatom or unsaturation is present in the molecular formula. Such structures must also then consider the presence of various functional groups.
Therefore, structural isomerism is divided into six easier subtypes to understand various attachment patterns –
1. Chain Isomerism
2. Position Isomerism
3. Functional Group isomerism
4. Metamerism
5. Tautomerism
6. Ring-chain isomerism
This method is analogous to dividing cooking into different techniques of boiling, braising, grilling, baking, stewing, etc., to make categorization easier. And you will come across such variations in techniques in a MasterChef competition!
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Next: Chain or Nuclear Isomerism
Next: Positional Isomerism
Next: Ring-chain Isomerism
Next: Functional Isomerism
Next: Metamerism
Next: Tautomerism
