Isomers

While studying organic chemistry, you must certainly have heard of isomerism. It is a very important topic and has a massive effect on the study of compounds. However, the different uses and applications of the concept may not have been covered in the course of the subject. To learn all about isomerism, its types, applications, and uses, read on. 

What are Isomers?

Isomers are chemical compounds that have the same chemical composition and same molecular formula but have different physical and sometimes different chemical properties. This is due to the different structural or spatial arrangement of the atoms in every molecule of the compound. The English word “Isomer” comes from the Greek term “Isomeros”, where  “isos” means “equal” and “méros” means “part”.

The concept of isomerism is widely used in the field of organic chemistry. This is one of the reasons why a wide variety of organic compounds exist, each having its own specific set of properties. Isomerism gives different compounds with the same molecular formula different properties, making scientists treat them and recognize them as different compounds. Isomers are compounds or polyatomic ions having the same molecular formula but different and distinct arrangements of atoms in space. Different isomers of a certain compound may show a huge difference in the various physical properties like the boiling point, melting point, optical rotation, etc, and also differences in chemical reactions they’re taking part in are widespread. Isomerism is still one of the most important and growing fields of organic chemistry.

Types of Isomers

Isomers are classified broadly into two categories – Structural or Constitutional Isomers and Stereoisomers. Let us learn about them in detail.

Stereoisomerism

Stereoisomers are those which have the same molecular bonding and composition, but the compounds have different orientations in space. In stereoisomerism, the relative position of the individual atoms is also taken into account. Apart from this, we also consider the rotations and translations of the atoms. 

The compounds showing stereoisomers can be further classified into compounds that 

show either geometric isomers or optical isomers.

You can read further about each of these kinds of isomers through online resources or through books on isomerism in organic chemistry. 

For example, let us consider an organic compound having the formula CPQRS and structure :

Now, if we alter the orientation of the atoms to get: 

The broad lines indicate that the atoms connected to the C-atom are oriented upwards from the plane of the paper, the dashed line indicates that the group or atom is oriented below the plane of the paper and the normal lines indicate that the atoms or group is on the plane of the paper. As we see, from the two stereoisomers, the orientations of the atoms have changed. Thus even though the connectivities of the atoms are the same, the orientations are different, thus they are stereoisomers or stereoisomers. The above example is of a compound showing optical isomerism. Geometric isomers have a great effect on the physical properties of the compound.

Structural Isomerism

Also known as constitutional isomers, structural isomers are compounds that have the same molecular formula but have differences in bondings of different groups. Though the atoms in a molecule are the same, the manner in which they are arranged and positioned is different. Structural isomerism gives rise to an innumerable number of compounds. Let us take the example of butane, which can be written in 2 ways – CH3-CH2-CH2-CH3 or n-butane and CH3-CH(CH3)-CH3 or 2-methylpropane. A chain with 10 carbons or decane can have as many as seventy-five structural isomers. 

Structural isomer can be further divided into five different types namely – 

• Chain Isomer
• Position Isomer
• Functional Isomer
• Metamerism
• Tautomerism

You can learn more about these from other online resources or from books on isomerism in organic compounds. 

Examples of Isomers

Let us take a few examples to understand the concept of isomerism

1. Chemical Formula: C3H8O

Possible structures:

2. Chemical Formula: C3H4

Possible Structures:

Conclusion

Now that you have a clear understanding of the concept of isomers, you should be ahead of many of your peers. Isomerism plays an important role in organic chemistry. Isomerism is one of the most important properties of organic compounds which isolates them from other compounds. As you shall see later, isomerism is also one of the key factors in deciding which organic compound would be able to perform the necessary function – for example, D-glucose is necessary for living organisms for the generation of energy in them, thus making it one of the most important beneficiary compounds, yet its isomer which is called L-glucose, can cause severe problems if ingested. Also, certain chemical reactions, especially the complex enzymatic reactions happening in our bodies can only proceed with one isomer of a particular compound and not with the other isomers. These above properties make isomerism and its study a very important topic in almost every biochemical research field in today’s world. The exact chemical and physical properties of a compound are highly dependent upon the content of its isomers as a mixture and also in determining which compound to use for a particular reaction. It is extremely vital in drug synthesis or making artificial substances and thus chemists have to be extremely careful to understand the importance of the stream.