The key difference between cis cyclohexane and trans cyclohexane is that cis cyclohexane has its substituents pointing to the same plane of the ring whereas trans cyclohexane has its substituents pointing to opposite planes.
Cyclohexane is a cycloalkane in which a six-membered carbon ring that exists in the chair conformation. In the chair conformation, this compound has the lowest angle strain; thus, it is more stable than other possible conformations. Moreover, in this conformation, half of the hydrogen atoms connected to carbon atoms are in the plane of the ring. We call this as equatorial positioning. The other half is located perpendicular to the plane of the ring. We call this axial positioning. When there are two or more substituents in cyclohexane, we can observe cis and trans isomerism by observing whether the substituents are in equatorial position or axial position.
CONTENTS
1. Overview and Key Difference
2. What is Cis Cyclohexane
3. What is Trans Cyclohexane
4. Side by Side Comparison – Cis vs Trans Cyclohexane in Tabular Form
5. Summary
What is Cis Cyclohexane?
Cis cyclohexane is a geometric isomer of the organic compound cyclohexane. The cyclohexane molecule should have two (or more) substituents in order to show this isomerism. If the two substituents groups are in the same plane (either equatorial or axial), then we call it the cis isomer of cyclohexane.
Figure 01: Cis and trans 1 methyl 4 hydroxymethyl cyclohexane
For example, if cyclohexane has a methyl group (-CH3) and hydroxyl group (-OH) in the axial plane, then we call it cis-1-methyl-4-hydroxymethyl cyclohexane. The structure of this isomer and the opposite (trans-isomer) are given in the image above.
What is Trans Cyclohexane?
Trans cyclohexane is a geometric isomer of cyclohexane which has its substituents in the opposite planes. That means; if one substituent is in the equatorial plane, the other substituent will be in the axial plane and vice versa. In the above example (in the isomers of 1 methyl 4 hydroxymethyl cyclohexane), the trans structure has methyl group in the equatorial plane while the hydroxyl group is in the axial plane.
What is the Difference Between Cis and Trans Cyclohexane?
Cyclohexane is an organic compound having six carbon atoms attached to each other via single covalent bonds, forming a six-membered ring. It can show cis-trans isomerism. The key difference between cis cyclohexane and trans cyclohexane is that cis cyclohexane has its substituents pointing to the same plane of the ring whereas trans cyclohexane has its substituents pointing to opposite planes. That means; if the substituents are in the equatorial plane (or in the axial plane), it is a cis isomer while if the substituents are in opposite planes (one substituent in the equatorial plane and the other in axial plane), then the isomer is trans.
Summary – Cis vs Trans Cyclohexane
Cyclohexane is an organic compound which can show cis-trans isomerism when it has two or more substituents. The key difference between cis cyclohexane and trans cyclohexane is that cis cyclohexane has its substituents pointing to the same face of the ring whereas trans cyclohexane has its substituents pointing to opposite faces.
Reference:
1. “4.2: Cis-Trans Isomerism in Cycloalkanes.” Chemistry LibreTexts, Libretexts, 23 May 2019, Available here.
Image Courtesy:
1. “Cis and trans 1 methyl 4 hydroxymethyl cyclohexane” By MarkForeman – Chemdraw drawing, Previously published here. (CC BY-SA 3.0) via Commons Wikimedia