Difference Between Benzene and Cyclohexane

The key difference between benzene and cyclohexane is that the benzene is an aromatic compound whereas the cyclohexane is a non-aromatic compound.

The scientist, Kekule found the benzene structure in 1872. Because of the aromaticity, benzene is different from other aliphatic compounds. Thus, it is a separate field of study in organic chemistry. On the other hand, though cyclohexane has a similar shape to benzene, it is not aromatic. Cyclohexane is a saturated alkane, which has different properties than benzene.

CONTENTS

1. Overview and Key Difference
2. What is Benzene
3. What is Cyclohexane
4. Side by Side Comparison – Benzene vs Cyclohexane in Tabular Form
5. Summary

What is Benzene?

Benzene has only carbon and hydrogen atoms arranged to give a planar structure. It has the molecular formula of C₆H₆.  Its structure and some of the important properties are as follows.

• Benzene is a colourless liquid with a sweet odour.
• It is flammable and evaporates quickly when exposed.
• Useful as a solvent, because it can dissolve a lot of non-polar compounds.
• It is slightly soluble in water.
• Delocalization of pi electrons.

Structure of Benzene

The structure of benzene is unique compared to other aliphatic hydrocarbons. Therefore, benzene has unique properties. All the carbons in benzene have three sp² hybridized orbitals. Two sp² hybridized orbitals of carbon overlap with sp² hybridized orbitals of adjacent carbons on either side. Other sp² hybridized orbital overlaps with the s orbital of hydrogen to form a σ bond.

Also, the electrons in p orbitals of carbon overlap with the p electrons of carbon atoms in both sides forming pi bonds. This overlap of electrons happens in all the six carbon atoms and, therefore, produces a system of pi bonds, which spread over the whole carbon ring. Thus, we say that these electrons become delocalized. The delocalization of the electrons means that there aren’t alternating double and single bonds. Therefore, all the C-C bond lengths are the same, and the length is between single and double bond lengths. As a result of the delocalization, benzene ring is stable, thus, reluctant to undergo addition reactions, unlike other alkenes.

The sources of benzene include natural products or various synthesized chemicals. Naturally, it occurs in petrochemicals like crude oil or gasoline. Concerning the synthetic products, benzene is present in some plastics, lubricants, dyes, synthetic rubber, detergents, drugs, cigarette smoke and pesticides. Benzene is released on burning of above materials. Therefore, automobile exhaust and factory emissions too contain benzene. Above all, it is carcinogenic, so exposure to high levels of benzene can cause cancer.

What is Cyclohexane?

Cyclohexane is a cyclic molecule with the formula of C₆H₁₂. Though it has a similar number of carbons like benzene, cyclohexane is a saturated molecule. Hence, there are no double bonds between carbons as in benzene. Also, it is a colourless liquid with a mild sweet odour.

Furthermore, we can produce this compound via the reaction between benzene and hydrogen. Since this is a cycloalkane, it is somewhat unreactive. Also, it is nonpolar and hydrophobic. Therefore, this is useful as a nonpolar solvent in the laboratory applications. Moreover, cyclohexane is one of the most stable cycloalkane, because its total ring strain is minimum. Thus, it produces the least amount of heat when burning compared to other cycloalkanes.

What is the Difference Between Benzene and Cyclohexane?

Benzene is an organic compound having the chemical formula C₆H₆ and a planar structure whereas cyclohexane is a cyclic molecule with the formula of C₆H₁₂. The key difference between benzene and cyclohexane is that benzene is an aromatic compound whereas cyclohexane is a non-aromatic compound. It is because, there are no double bonds between carbon atoms in the cyclohexane ring. Another important difference between benzene and cyclohexane is that the benzene is an unsaturated molecule while cyclohexane is a saturated molecule. It is because benzene has carbon atoms in the ring with sp² hybridization whereas cyclohexane has carbon atoms in the ring with sp³ hybridization.

The below infographic of difference between benzene and cyclohexane shows more differences between the two.

Summary – Benzene vs Cyclohexane

Benzene and cyclohexane are both six-membered ring structures. But they differ from each other according to the chemical bonding between carbon atoms; thus, the geometry of the molecules. Since the bonding between carbon atoms determines the aromaticity of molecules, we can emphasize that the key difference between benzene and cyclohexane as; benzene is an aromatic compound whereas cyclohexane is a non-aromatic compound.

Reference:

1. “Benzene.” Wikipedia, Wikimedia Foundation, 27 Sept. 2018. Available here  
2. “Cyclohexane.” Wikipedia, Wikimedia Foundation, 10 Oct. 2018. Available here  

Image Courtesy:

1.”Benzene-aromatic-3D-balls”By Benjah-bmm27 – Own work, (Public Domain) via Commons Wikimedia
2.”Cyclohexane-chair-3D-balls” (Public Domain) via Commons Wikimedia