Cis-trans Relationship in Cyclohexane

The main distinction between cis and trans cyclohexane is that the substituents in cis cyclohexane point in the same ring plane, whereas the substituents in trans cyclohexane point in opposing planes. Cyclohexane is a chair-conformed cycloalkane having a six-membered carbon ring. This compound has the lowest angle strain in the chair conformation, making it more stable than other potential conformations. Furthermore, half of the hydrogen atoms linked to carbon atoms are on the ring’s plane in this configuration. The equatorial or axial positions of the substituents in cyclohexane can be utilized to determine cis and trans isomerism if there are two or more substituents.

Define cis-trans isomers

The chemical compound cyclohexane has a geometric isomer called cis cyclohexane. Isomerism requires two (or more) substituents in the cyclohexane molecule. The cis isomer of cyclohexane is defined as two substituent groups in the same plane (either equatorial or axial). In the axial plane, cis-1-methyl-4-hydroxymethyl cyclohexane is cyclohexane containing a methyl group (-CH3) and hydroxyl group (-OH).

The geometric isomer of cyclohexane having substituents on opposite planes is trans cyclohexane. To put it another way, if one substituent is in the equatorial plane, the other is in the axial plane, and vice versa. The methyl group is in the equatorial plane in the trans structure of 1 methyl 4 hydroxymethyl cyclohexane isomers, whereas the hydroxyl group is in the axial plane.

The cis-trans isomer is a steric isomer in which the atoms are structured differently in three-dimensional space. Trans isomers have functional groups on the opposite side of the carbon chain, whereas cis isomers have functional groups on the same side of the carbon chain. Both organic and inorganic compounds can undergo this form of isomerization. Each double bond carbon atom can only have two separate atoms or groups of atoms for cis and trans isomers to exist.

Properties of Cis-trans isomers

A molecule’s cis-trans isomers exhibit a wide range of physical properties. Different dipole moments in the molecule or different spatial arrangements of the atoms can create these variances. 

• The cis isomer of pentene has a boiling point of 37°C, while the trans isomer has a boiling point of 36°C. The difference is minor due to the low bond polarity.
• The cis isomer of dichloroethylene has a boiling temperature of 60.3°C and the trans isomer of dichloroethylene has a boiling point of 47.5°C due to the polarity of the 1,2-dichloroethylene link. Butenedioic acid’s cis and trans isomers exhibit a wide spectrum of reactivity. Several factors have led to this.
• Fumaric acid is the trans isomer, while Maleic acid is the cis isomer. Elaidic and oleic acids have cis-trans isomers. The former is a solid at room temperature (melting point = 43°C), whereas the latter is a liquid (melting point= 13.4°C). The melting point of trans isomers is higher than that of cis isomers.
• In fundamentally inert solvents, they are easily soluble. Trans isomers are thought to have a lower density than cis isomers.
• Because the trans isomers’ unique bond dipole values are on opposite sides, they cancel each other out. The trans isomers are more stable than the acyclic cis isomers.

Examples of cis-trans isomers

• Organic Compound: Cis-trans isomerism is caused by the presence of a double or triple bond within a molecule, which limits bond rotation. This isomerism can be seen in the chemical compound but-2-ene.

• Inorganic compound: Several diazenes and diphosphenes have cis-trans isomers. In coordination complexes with square planar or octahedral geometries, the placement of the ligands generates cis-trans isomerism.

Conclusion

The cis isomers are molecules with identical atomic links. Substituent steric interaction can explain this. They suggest page groups on the same side of the double bond that are similar. Trans isomers, on the other hand, have side groups on the other side of the double bond that are similar. The longest double-bond chain can be utilised to determine the cistrans isomer. The isomer is cisalken if the two groups linked to the carbon of the double bond are on the same side of the double bond. The isomer is a trans alkene when the two groups are on opposite sides of the double bond.