Difference Between Cyclohexane and Benzene

Main Difference – Cyclohexane vs Benzene

Cyclohexane and benzene are two important organic compounds that have many applications in chemical synthesis processes. Both are composed of six carbon atoms and are cyclic structures. Since the 2D chemical structure of cyclohexane and benzene looks somewhat similar, their structures and names are often confusing. However, there are many differences between cyclohexane and benzene. The main difference between cyclohexane and benzene is that cyclohexane contains twelve hydrogen atoms bonded to six carbon atoms, two hydrogen atoms per each carbon atom whereas benzene contains six hydrogen atoms bonded to six carbon atoms, one hydrogen atom per each carbon atom.

Key Areas Covered

1. What is Cyclohexane
     – Definition, Chemical Properties, Structure, Synthesis
2. What is Benzene
     – Definition, Chemical Properties, Structure
3. What is the Difference Between Cyclohexane and Benzene
     – Comparison of Key Differences

Key Terms: Aromatic, Atom, Benzene, Crude Oil, Cyclic, Cyclohexane, Hybridization, Octane Number

What is Cyclohexane

Cyclohexane is an organic compound having the chemical formula C₆H₁₂ and is a cyclic structure. It is a cycloalkane, which means, cyclohexane is a saturated compound having no double or triple bonds in its structure and is a cyclic compound. Therefore, all carbon atoms in cyclohexane are sp³ hybridized.

Although the 2D structure of cyclohexane seems planar, it is actually not so. The chemical structure of cyclohexane is given in the image below. This structure is known as chair conformation. This conformation is the most stable structure for cyclohexane where the torsional strain has been minimized.

Figure 1: Cyclohexane has no Planar Structure

The molar mass of cyclohexane is 84.16 g/mol. It is a colorless liquid at room temperature. Cyclohexane has a sweet, but gasoline-like odor. The melting point of cyclohexane is 6.47 °C, and the boiling point is 80.74 °C. It is immiscible with water but is soluble in solvents such as ether, alcohol and acetone.  

Cyclohexane cannot be found in natural resources like crude oil. Therefore cyclohexane should be synthesized. In industrial scale, cyclohexane is produced by hydrogenation of benzene. It is simple and easy because both benzene and cyclohexane are cyclic structures composed of six carbon atoms. However, the reaction is highly exothermic.

Cyclohexane is a major raw material for the production of adipic acid and caprolactam. These compounds are the precursors used in nylon production. Cyclohexane is also used as a nonpolar solvent in laboratories. 

What is Benzene

Benzene is a very common and important organic molecule having the chemical formula C₆H₆. It is composed of six carbon atoms which are sp² hybridized, and each of this carbon atom is bonded to two other carbon atoms and a hydrogen atom. Hence it is a planar structure. At room temperature, it is a colorless liquid.

The molar mass of benzene is 78.11 g/mol. Benzene is an aromatic compound. It has an aromatic odor; it is a gasoline-like odor. The melting point of benzene is 5.53 °C, and the boiling point is 80.1 °C. It is not miscible with water. but it is soluble in alcohol, chloroform, diethyl ether, etc.

Figure 2: Benzene Facts

In its chemical structure, benzene has delocalized pi electron clouds parallel to the plane of the molecule. This happens due to the presence of un-hybridized p orbitals present in each carbon atom of the benzene ring. These pi orbitals can mix with each other, forming an electron cloud.

Benzene can be found naturally in crude oil. Benzene is highly flammable. It is an aromatic hydrocarbon. Since benzene has a high octane number, it is an important constituent in gasoline. The major use of benzene is its use as an intermediate for the production of other chemicals such as ethylbenzene, cumene, etc.

Difference Between Cyclohexane and Benzene

Definition

Cyclohexane: Cyclohexane is an organic compound having the chemical formula C₆H₁₂.

Benzene: Benzene is a very common and important organic molecule having the chemical formula C₆H₆.

Number of Hydrogen Atoms

Cyclohexane: Cyclohexane has 12 hydrogen atoms.

Benzene: Benzene has six hydrogen atoms.

Structure

Cyclohexane: Cyclohexane has chair conformation.

Benzene: Benzene is a planar structure.

Molar Mass

Cyclohexane: The molar mass of cyclohexane is 84.16 g/ mol.

Benzene: The molar mass of benzene is 78.11g/mol.

Melting Point and Boiling Point

Cyclohexane: The melting point of cyclohexane is 6.47 °C and the boiling point is 80.74 °C.

Benzene: The melting point of benzene is 5.53 °C and the boiling point is 80.1 °C.

Hybridization of Carbon Atoms

Cyclohexane: Cyclohexane has sp³ hybridized carbon atoms.

Benzene: Benzene has sp² hybridized carbon atoms.

Delocalized Pi Electrons

Cyclohexane: There are no delocalized pi electron clouds in cyclohexane

Benzene: There are delocalized pi electron clouds in benzene.

Occurrence

Cyclohexane: Cyclohexane does not naturally occur in crude oil.

Benzene: Benzene naturally occurs in crude oil.

Conclusion

Cyclohexane and benzene are six carbon-cyclic structures. Although their 2D structures look similar, they are very different compounds. The main difference between cyclohexane and benzene is that cyclohexane contains 12 hydrogen atoms bonded to six carbon atoms, two hydrogen atoms per each carbon atom whereas benzene contains six hydrogen atoms bonded to six carbon atoms, one hydrogen atom per each carbon atom.

Reference:

1. “CYCLOHEXANE.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.
2. “Benzene.” Wikipedia, Wikimedia Foundation, 18 Jan. 2018, Available here.

Image Courtesy:

1. “Cyclohexane with H” By Calvero. – Selfmade with ChemDraw (Public Domain) via Commons Wikimedia
2. “Benzene Representations” By Vladsinger – Own vector drawing based on layout of en:File:Benzol trans.png (CC BY-SA 3.0) via Commons Wikimedia