Difference Between Cis and Trans Isomers

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Cis vs Trans

When we study the isomers in chemistry, we come across different forms of isomers. Although isomers are divided into two different groups - stereoisomers and constitutional isomers, there are other sub-divisions of isomers as well, such as cis and trans isomers. However, there is a difference between cis and trans isomers.

Generally, the cis and trans isomerism is found in both organic and inorganic compounds. Cis isomers are the isomers that have two similar atoms lying on the same side of the double bond in a molecule. The trans isomers have molecules with two similar atoms that are placed on opposite sides of the double bond. Both the cis and trans isomers possess the same molecular formula but differ in a few aspects. In this article, we will learn about the difference between cis vs trans-isomers.

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What is Cis and Trans Form of Isomers?

The atoms that make up isomers in stereoisomerism join up in the same order, but have a different spatial arrangement. Geometric isomerism is a type of stereoisomerism.

These kinds of isomers tend to occur when the rotation in a molecule is restricted. The examples of stereoisomers generally consist of the carbon-carbon double bond.

Talking about the difference between the cis and trans stereoisomers, the main difference between the two lies in the arrangement of the atoms in the double bonds. However, some of the major difference between the isomers cis and trans are tabulated below. Let us take a look at them.

Difference Between Cis and Trans Isomers



Cis isomers are referred to as the molecules having the same connectivity of the atoms. They constitute similar side groups that are placed on the same side of the double bond.

Trans isomers, on the other hand, consist of molecules having similar side groups that are placed on opposite sides of the double bond.

Cis isomers are generally almost polar.

Trans isomers are not much polar. Many of the known trans isomers are non-polar molecules.

Because of the loosely packed molecules, the cis isomers possess relatively lower melting points when compared to the trans-isomers.

Because of the tightly packed molecules, the melting points of the trans isomers are generally higher than that of the cis isomers.

Similarly, because of the presence of the strong attractive forces between the two atoms, the cis isomers tend to possess a higher boiling point.

The boiling point of the trans isomers is comparatively low since there are no such strong attractive forces.

In the inert solvents, the cis isomers tend to possess a strongly soluble content.

The solubility of the trans isomers in neutral solvents is relatively smaller.

Both the forms of the cis isomers possess a higher acid power.

The protons in the trans isomers are not readily emitted. Hence, it has a lesser acidic strength.

FAQ (Frequently Asked Questions)

1. What are Isomers?

Ans: The definition of isomers is given as follows.

Isomers refer to the molecules twitch tend to possess the same molecular formula but a different spatial arrangement of the atoms. This means that it excludes all the different arrangements that are just because of the molecules that are rotating as a whole unit or are rotating around the particular bonds. When the atoms that make up the different isomers tend to join together but in a different order, it is referred to as the structural isomerism. However, it is important to know that structural isomerism is not a type of stereoisomerism.

2. What are Stereoisomers?

Ans: Stereoisomers refer to the isomers which possess the same composition but have a varying orientation. This means that they possess the same parts but the spatial arrangement of these parts have a different orientation. There are two different types of stereoisomers, namely, enantiomers and diastereomers. Enantiomers are the stereoisomers that have mirror images, similar to the human hand, whereas diastereomers are the isomers other than the mirror images. However, the energy required and timescale are essential. These isomers tend to occur when the rotation is restricted in the given molecule. At the introductory level in regards to organic chemistry, the examples of these isomers generally involve the double bonds of the carbon-carbon molecules.

3. How to get Geometric Isomers?

Ans: To achieve geometric isomers, there are a few things to be considered. These are as follows:

  1. The rotation must be restricted, which includes the carbon-carbon double bond.

  2. There must be two different groups on the left-hand side of the carbon-carbon bond and similarly, two different groups on the right-hand side as well. However, the groups on the left side don’t need to be the same as the groups on the right side.

Hence, if we keep in mind the things that are mentioned above, we can easily achieve the geometric isomers of an organic or an inorganic compound.

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