Difference Between Congener and Isomer

The key difference between congener and isomer is that the congener refers to chemical compounds having similar structures and similar properties. Meanwhile, isomer refers to molecules having the same chemical formula but different structures.

The terms congener and isomer refer to groups of compounds which are grouped according to their similarities. The term congener may have different definitions, but in chemistry, we mostly use the definition that states congeners are chemical compounds having similar structures and similar properties. Isomers, on the other hand, are compounds having different structures but similar atomic composition; hence, they have different properties as well.

CONTENTS

1. Overview and Key Difference
2. What is Congener 
3. What is Isomer 
4. Side by Side Comparison – Congener vs Isomer in Tabular Form
5. Summary

What is Congener?

Congener is a term that refers to chemical compounds having similar structures and similar properties. However, this term sometimes refers to the members of the same group in the periodic table of elements. For example, polychlorinated biphenyls are a class of chemical compounds which has about 200 congeners. Similarly, there are polybrominated biphenyls, which is a different class of compounds containing compounds having the same chemical structure with similar chemical properties. These chemical compounds are related to each other in origin, structure, or function.

We can categorize these classes of compounds according to the origin, structure or function. For example, there are congener alcohols which form during fermentation. So, this is the classification based on the origin of the compound. Similarly, we can classify congeners of oleic acid according to the function; they can modify the cell membrane of animal cells to prevent tumours. Moreover, we can classify the compounds depending on the structure. For example, potassium chloride and sodium chloride can be considered as congeners because they have similar valences and yield similar structures.

What is Isomer?

Isomer is a term that refers to compounds having similar chemical formulas but different structures. These isomers can be either ions or molecules. A compound having different isomers is known as isomerism. There are two major types of isomerism: structural isomerism and stereoisomerism.

Structural isomerism or constitutional isomerism is the property of having different connectivity of atoms for the same chemical formula. For example, propanol and methoxyethane have the same chemical formula C₃H₈O, but they have different structures and different functional groups. Stereoisomers are compounds having similar chemical formulas, similar connectivity of atoms but different geometries. There are two types of stereoisomers as enantiomers and diastereomers. These are different from each other, depending on the presence or absence of chiral centres, non-superposable mirror images, etc.

What is the Difference Between Congener and Isomer?

The terms congener and isomer refer to the groups of compounds that are categorized according to their similarities. However, the key difference between congener and isomer is that the congeners refer to chemical compounds having similar structures and similar properties, whereas isomers refer to molecules having the same chemical formula but different structures. Therefore, congeners have similar structures, while isomers have similar chemical formulas but different structures. If we consider some examples, potassium chloride and sodium chloride are congeners in valency and structure, while alcohols are similar in origin. Meanwhile, propanol and methoxyethane are structural isomers.

Below is a summary of the difference between congener and isomer.

Summary – Congener vs Isomer

The terms congener and isomer refer to the groups of compounds which are categorized according to their similarities. The key difference between congener and isomer is that the term congener refers to the chemical compounds having similar structures and similar properties, whereas the term isomer refers to the molecules having the same chemical formula but different structures.

Reference:

1. Helmenstine, Anne Marie. “Congener Definition and Examples.” ThoughtCo, Dec. 5, 2018, Available here.
2. Jones, Maitland. “Isomerism.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 18 Oct. 2016, Available here.

Image Courtesy:

1. “Polychlorinated biphenyl structure” By D.328 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Cisplatin and transplatin” By Anypodetos – Own work (CC0) via Commons Wikimedia