Difference Between Cis and Trans Fatty Acids

The key difference between cis and trans fatty acids is that the cis fatty acids have two hydrogen atoms attached to the double bond in the same side of the carbon chain whereas the trans fatty acids have the two hydrogen atoms bonded to the double bond in the opposite sides of the carbon chain.

Fatty acids are carboxylic acids containing long aliphatic carbon chains that are either saturated or unsaturated. This means, the aliphatic chain may or may not contain double bonds between the carbon atoms. Cis and trans fatty acids are two forms of unsaturated fatty acids.

CONTENTS

1. Overview and Key Difference
2. What is Cis Fatty Acids
3. What is Trans Fatty Acids
4. Side by Side Comparison – Cis vs Trans Fatty Acids in Tabular Form
5. Summary

What is Cis Fatty Acids?

Cis fatty acids are carboxylic acids containing long aliphatic carbon chains having the two hydrogen atoms attached to double bond in the same side of the carbon chain. We name this as the “cis configuration of unsaturated fatty acids”.

Since the hydrogen atoms are on the same side of the carbon chain, it causes the chain to bend. This restricts the conformational freedom of the fatty acid. If there are many double bonds in the chain, it lessens the flexibility of the chain. Moreover, if there are more cis configurations along the carbon chain, it makes the chain quite curved in its most accessible conformations. Examples include cis-oleic acid and cis-linoleic acid.

What is Trans Fatty Acids?

Trans fatty acids are carboxylic acids containing long aliphatic carbon chains having the two hydrogen atoms attached to double bond in the opposite sides of the carbon chain. Therefore, this does not cause the carbon chain to bend much.

Figure 01: Comparison of Cis and Trans Configurations of Oleic Acid

Moreover, their shape is similar to straight saturated fatty acids. The trans fatty acids are not that much common in nature as cis configuration. It forms mainly as a result of industrial production. For example, hydrogenation reactions may cause the formation of trans fatty acids.

What is the Difference Between Cis and Trans Fatty Acids?

Cis fatty acids are carboxylic acids containing long aliphatic carbon chains having the two hydrogen atoms attached to double bond in the same side of the carbon chain whereas the trans fatty acids are carboxylic acids containing long aliphatic carbon chains having the two hydrogen atoms attached to double bond in the opposite sides of the carbon chain. This is the key difference between cis and trans fatty acids. Furthermore, when considering their occurrence, cis configuration is much common in nature while the trans configuration is not common in nature. Because, the trans fatty acids mainly form as a result of different industrial processes such as hydrogenation. Moreover, another difference between cis and trans fatty acids is that the cis configuration causes the fatty acid molecule to bend while the trans configuration does not cause the molecule to bend much.

Summary – Cis vs Trans Fatty Acids

Fatty acids are mainly in two types of saturated and unsaturated fatty acids. We can categorize unsaturated fatty acids further, as cis and trans fatty acids. The difference between cis and trans fatty acids is that the cis fatty acids have two hydrogen atoms attached to the double bond in the same side of the carbon chain whereas the trans fatty acids have the two hydrogen atoms bonded to the double bond in the opposite sides of the carbon chain.

Reference:

1. “Fatty Acid.” Wikipedia, Wikimedia Foundation, 24 Aug. 2018. Available here
2. “The Kinds of Fats.” Indiana University Bloomington, The Lilly Library, Indiana University. Available here 

Image Courtesy:

1.”Isomers of oleic acid”By Edgar181 – Own work, (Public Domain) via Commons Wikimedia  

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