What Is Isomerism?
Before we dive into the intricacies of isomerism, let’s take a look at what isomerism is. Say you have 5 beads that you need to make a necklace. Out of five beads, three are red, and two are blue. You can arrange these beads in any way you want to. You can place three reds, and then two blues, or you can also put two reds, then one blue, two reds and then one blue. They are made of the same constituents, and yet, they are different. Isomers are exactly this. They are molecules with the same chemical formulae but with a different chemical structure. Isomers are molecules that have the same molecular formula but have a different arrangement of atoms in space.
This means a different arrangement, entirely and not just a changed orientation or the slight rotation of the constituents of the molecules. Isomers do not necessarily share similar properties unless they have the same functional groups, in the case of isomerism in organic chemistry. Isomerism is widely studied in organic chemistry and has a huge application in chemistry and medicine. Let’s take a look at one specific group of isomerism – structural isomerism.
Structural Isomerism
Structural isomerism is the type of isomerism where the atoms and the functional groups are joined together in different ways. This means that when you compare two structural isomers, the atoms and the functional groups are located at different places. In structural isomerism, the atoms are arranged in a completely different order. In organic chemistry, the relocation can occur with atoms, functional groups or even carbon atoms which are an integral part of the chain. There are a few types of structural isomers, and let us learn about them.
Chain Isomerism
A chain isomerism is observed when the carbon molecules in the chain of an organic molecule are relocated, which alters the chain of the organic compound. The images shown below are examples of chain isomerism. The first row represents the chemical, pictorial and formula representation of n-butane, whereas the second row represents that of isobutane. As you can see, they are both made of the same number of carbon and hydrogen atoms, but the chain of carbon molecules is altered due to the attachment of the carbon molecule at a different point. The number of possible structural isomers increases greatly with the number of available atoms. There are only two butanes, but there are three pentanes (C5H12), 18 octanes (C8H18) and so on.
Positional Isomerism
Organic molecules usually have functional groups attached at the terminals, such as halogen atoms, hydroxyl atoms, etc. The relocation of these functional groups between two identical organic compounds gives rise to positional isomerism. A simple example of this type of isomerism would be
The above images represent various positional isomers of propanol. The formula for propanol is C3H7OH or C3H8O. Note that in the above images, in the first two, the position of the hydroxyl group (-OH) is changed, leading to the creation of two positional isomers. Positional isomerism can also be observed in cyclic organic compounds, such as benzene rings and other such aromatic compounds.
Functional Isomerism
In functional isomerism, the same sets of atoms are re-arranged in such a way that the two functional isomers have significantly different properties from each other due to their containing different functional groups. This means that they belong to different families of compounds. To understand this better, let’s recall the propanol molecule.
Although both molecules contain the same constituents, the second organic compound has a completely different arrangement of atoms. More importantly, the oxygen here is connected to two carbons instead of hydrogen and carbon, which makes it an ether, not an alcohol like the first compound. In this article, we learnt about isomerism, isomers and the various types of structural isomerism, such as chain isomerism, positional isomerism and functional isomerism. To learn more, visit BYJU’S website, and fall in love with learning.
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