Effect of Multiple Substitutions

Cyclohexanes are hydrocarbon compounds; these compounds can be chemically written by the cyclohexane formula, C6H12. Cyclohexanes can be defined by their many physical and chemical properties. 

Cyclohexane compounds are poorly soluble in alcohol and water and have a pleasant smell. Depending on the ring structure and the placement of the functional groups, the cyclohexanes can have multiple substitutes. In general, the functional groups in cyclohexane occupy axial or equatorial positions.

In the following article, we will learn about multiple substitutes of cyclohexanes and their effects on cyclohexane stability.

Cyclohexane

Before diving into the properties and features of multiple substitutes of cyclohexane, let us first understand what these compounds are.

Cyclohexane is a hydrocarbon compound; some of the general properties of cyclohexanes are given below.

• Cyclohexane is used as a solvent to dissolve various compounds, such as ethers, fats, resins, etc.

• Cyclohexane is also used in the production of Nylon 66.

• The composition of cyclohexane compounds can be determined by the cyclohexane formula or the chemical formula of cyclohexane. The cyclohexane formula is written as C6H12.

• A simple structure of cyclohexane looks like a perfect hexagon.

Physical Properties

• Cyclohexanes do not have any colour to them.

• They are found in the form of mobile liquids.

• They have a slight sweet smell.

• Cyclohexanes are little to no soluble in alcohol compounds and water.

Chemical Properties

• Cyclohexanes are highly flammable (prone to catch fire) compounds.

• Cyclohexanes are non-corrosive liquids.

• Cyclohexanes possess multiple substitutes depending on the molecular ring structure of the cyclohexane compound.

Substituted Cyclohexane

Multiple substitutes of cyclohexanes can be found depending on the molecular configuration of the compounds in the ring structure of cyclohexane.

• The multiple substitutes of cyclohexane are found either in axial or equatorial positions in the conformations of the ring structure.

• Six out of twelve hydrogen atoms are placed in an axial position in a general Cyclohexane ring structure.

• The other six hydrogen atoms in the cyclohexane ring structure are placed in the equatorial positions.

• This configuration gives a two-chair conformation for the Cyclohexane compound, which is interchangeable at room temperatures.

• However, for multiple substitutes of cyclohexane, the two-chair conformations of atoms do not apply. 

The concept of substituted cyclohexanes can be explained by considering the example of a  methylcyclohexane compound.

• In general, a methylcyclohexane ring structure possesses a two-chair conformation of compounds.

• This conformation is interchangeable by flipping the methylcyclohexane ring structure.

• The methyl group (functional group) is placed at an axial position in the ring structure in the initial conformation of methylcyclohexane.

• However, we discover that the methyl group occupies an equatorial conformation upon flipping the ring.

Studies have shown that the equatorial conformation of methylcyclohexane (C7H14) is much more stable than the axial conformation of the same compound.

Stability of Substituted Cyclohexane

Cyclohexane stability can be determined by the conformations of its compounds in the ring structure. 

Studies have shown that the equatorial conformations are more stable among the multiple substitutes of cyclohexanes than the axial confirmation. 

The following points can explain the cyclohexane stability in equatorial conformation.

• The two-chair conformation of cyclohexanes can undergo an interchange at room temperature conditions.

• In general, both conformations have similar physical and chemical properties; the energy exhibited by the two conformations is almost equal.

• However, introducing a functional group to the cyclohexane makes the two-chair conformation unbalanced.

• In the above example of methylcyclohexane (C7H14), the methyl group (CH3) occupies an axial position in the prior chair conformation, and later, it occupies the equatorial position in chair conformation. 

• This causes non-equivalent energies between the two-chair conformation of methylcyclohexane compounds.

• The energy difference causes the methyl group at an axial position to rise in energy level by 7.6 kJ/mol in the compound.

• This results in a more stable equatorial conformation of the methyl group.

1,3-diaxial interactions are responsible for the difference in energy between two conformations of the methyl group or functional groups.

The 1,3-diaxial interaction is caused when the carbon atoms at positions 1,3 and 5 undergo steric strain; here, this strain is caused by the introduction of the methyl functional group. 

As the methyl group is introduced in an axial position, it produces steric strain to carbon atoms placed at 1, 3, and 5 positions, and the resulting strain causes an increase in energy.

However, when the methyl functional group is positioned at an equatorial conformation, the position is anti to carbon 3 and 5; this results in less energy and cyclohexane stability.

Conclusion

Cyclohexanes are chemical compounds consisting of Carbon and Hydrogen atoms. As per the chemical formula, cyclohexanes can be written by the cyclohexane formula, C6H12. The position of the functional group interacting with given cyclohexane determines multiple substitutes for cyclohexanes. 

In the given article, we try to understand the multiple substitutes and their effects on cyclohexane stability. Here we look into the example of methylcyclohexane compounds. The equatorial position of the functional group provides more cyclohexane stability than the axial placing.