Sign In

3.13 : Disubstituted Cyclohexanes: cis-trans Isomerism

Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.

In cyclohexane, the substituents can occupy different positions generating distinct isomers. For instance, in the case of 1,4-dimethylcyclohexane, the cis isomer has two conformers equilibrating in equal proportions. Both conformers have one methyl group in the axial and the other in the equatorial positions. However, the conformers of the trans isomer are energetically non-equivalent. The trans conformer having both the methyl groups in the axial position experiences strong steric repulsion and is less stable than the diequatorial form. Hence the trans-diequatorial form is most abundant at equilibrium.

The isomers of 1,2-dimethylcyclohexane are similar to that of 1,4 counterparts. The trans-1,2-dimethylcyclohexane has two energetically non-equivalent conformers. Due to the absence of 1,3-diaxial interactions, the diequatorial form is more stable and abundant than the diaxial conformer. In contrast, both conformers of the cis-isomer have equivalent energies with one axial and one equatorial methyl group.

The presence of bulky substituents alters the equilibrium because the bulky substituent preferentially occupies the equatorial position to avoid the strong steric repulsion in the axial position.

Tags
Disubstituted CyclohexanesCis trans IsomerismStereoisomersPhysical PropertiesCarbon carbon Bonds14 dimethylcyclohexaneCis IsomerTrans IsomerEquilibrating ConformersAxial PositionEquatorial PositionSteric RepulsionDiequatorial FormTrans diequatorial Form12 dimethylcyclohexaneDiaxial InteractionsBulky Substituent

From Chapter 3:

article

Now Playing

3.13 : Disubstituted Cyclohexanes: <em>cis-trans</em> Isomerism

Alkanes and Cycloalkanes

10.1K Views

article

3.1 : Structure of Alkanes

Alkanes and Cycloalkanes

22.1K Views

article

3.2 : Constitutional Isomers of Alkanes

Alkanes and Cycloalkanes

16.3K Views

article

3.3 : Nomenclature of Alkanes

Alkanes and Cycloalkanes

15.7K Views

article

3.4 : Physical Properties of Alkanes

Alkanes and Cycloalkanes

9.4K Views

article

3.5 : Newman Projections

Alkanes and Cycloalkanes

13.2K Views

article

3.6 : Conformations of Ethane and Propane

Alkanes and Cycloalkanes

11.5K Views

article

3.7 : Conformations of Butane

Alkanes and Cycloalkanes

11.4K Views

article

3.8 : Cycloalkanes

Alkanes and Cycloalkanes

10.4K Views

article

3.9 : Conformations of Cycloalkanes

Alkanes and Cycloalkanes

10.1K Views

article

3.10 : Conformations of Cyclohexane

Alkanes and Cycloalkanes

9.8K Views

article

3.11 : Chair Conformation of Cyclohexane

Alkanes and Cycloalkanes

11.9K Views

article

3.12 : Stability of Substituted Cyclohexanes

Alkanes and Cycloalkanes

10.7K Views

article

3.14 : Combustion Energy: A Measure of Stability in Alkanes and Cycloalkanes

Alkanes and Cycloalkanes

5.8K Views

JoVE Logo

Privacy

Terms of Use

Policies

Research

Education

ABOUT JoVE

Copyright © 2025 MyJoVE Corporation. All rights reserved