The key difference between open chain and closed chain hydrocarbons is that the open chain hydrocarbons are not cyclic structures, whereas the closed chain hydrocarbons are cyclic structures.
Hydrocarbon compounds are organic compounds having carbon and hydrogen atoms. The simplest hydrocarbon compound must have a carbon atom and one or more hydrogen atoms. Generally, we can see carbon-carbon bonds in hydrocarbon compounds.
CONTENTS
1. Overview and Key Difference
2. What are Open Chain Hydrocarbons
3. What are Closed Chain Hydrocarbons
4. Open Chain vs Closed Chain Hydrocarbons in Tabular Form
5. Summary – Open Chain vs Closed Chain Hydrocarbons
What are Open Chain Hydrocarbons?
Open chain hydrocarbons are organic compounds made of carbon and hydrogen atoms, and these compounds are acyclic (not cyclic compounds). Open chain hydrocarbons are mostly linear structures. There can be open chain hydrocarbons that have side chains. If there are no side chains attached to this type of hydrocarbon, we call it a straight-chain hydrocarbon. Typically, open chain hydrocarbons are aliphatic structures.
Figure 01: Two Compounds at the Top are Open Chain Hydrocarbon Structures while the Others are their Cyclic Forms
Generally, simple molecules in organic chemistry such as alkanes and alkenes have both linear and ring isomers. This means there are both cyclic and acyclic compounds. Often, cyclic compounds exist as aromatic hydrocarbons. Hydrocarbons having more than four carbon atoms per molecule may or may not contain side chains. Therefore, these simple hydrocarbons may occur either in straight-chain form or branched-chain form. Moreover, when naming the open chain hydrocarbons, we use the prefix n- to describe the straight-chain isomer. We can use the prefix i- to name the iso-form of the compound, which is the branched structure of the open chain hydrocarbon.
Furthermore, not all the open chain hydrocarbon compounds are literally straight. This is because their bond angles are not always 180 degrees. But the name open chain or straight chain reflects that the compound is schematically straight. There can be wavy or puckered structures of open chain hydrocarbons.
What are Closed Chain Hydrocarbons?
Closed chain hydrocarbons or cyclic hydrocarbons are ring structures made of mainly carbon and hydrogen atoms. In these molecules, the carbon atoms link with each other joining to form a cyclic structure. Moreover, closed chain hydrocarbons can be aromatic or non-aromatic compounds.
Figure 02: A Cycloalkane
We can represent the structural formula of closed chain hydrocarbons in multiple ways. We can represent them with or without showing bond angles. The simplest closed chain hydrocarbons are cycloalkanes. Cycloalkanes have all carbon-carbon bonds as single bonds. They are saturated compounds as well. On the other hand, cycloalkenes are closed chain hydrocarbons with at least one C=C bond. Similarly, cycloalkynes are closed chain hydrocarbons with at least one carbon to carbon triple bond.
What is the Difference Between Open Chain and Closed Chain Hydrocarbons?
Open chain and closed chain hydrocarbon compounds are the two major forms of hydrocarbons. The key difference between open chain and closed chain hydrocarbons is that the open chain hydrocarbons are not cyclic structures, whereas closed chain hydrocarbons are cyclic structures. Moreover, open chain hydrocarbons, there are terminal functional groups in the main carbon chain, while in closed chain hydrocarbons, there are no terminal functional groups in the main carbon chain. Also, another difference between open chain and closed chain hydrocarbons is that the open chain hydrocarbons are non-aromatic, but the closed chain hydrocarbons are can be either, aromatic or non-aromatic.
The following table summarizes the difference between open chain and closed chain hydrocarbons.
Summary – Open Chain vs Closed Chain Hydrocarbons
A hydrocarbon compound essentially contains one or more carbon atoms and hydrogen atoms. Generally, well-known hydrocarbon compounds have carbon-carbon covalent bonds. The key difference between open chain and closed chain hydrocarbons is that open chain hydrocarbons are not cyclic structures, whereas closed chain hydrocarbons are cyclic structures.
Reference:
1. “25.6: Cyclic Hydrocarbons.” Chemistry LibreTexts, Libretexts, 2 June 2021.
Image Courtesy:
1. “Cyclobutane-buckled-3D-balls” By Ben Mills – Own work (Public Domain) via Commons Wikimedia
2. “HexosesHemiacetal” By Karlhahn – Own work (Public Domain) via Commons Wikimedia
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