The key difference between straight and branched chain alkanes is that in straight-chain alkanes, all the carbon atoms bond with each other forming a continuous chain whereas branched-chain alkanes have side chains attached to a continuous carbon chain.
Alkanes are hydrocarbon compounds containing carbon and hydrogen atoms with only single bonds between them (no double bonds or triple bonds between carbon atoms). Based on their structure, there are two types of alkanes as straight chain alkanes and branched-chain alkanes.
CONTENTS
1. Overview and Key Difference
2. What are Straight Chain Alkanes
3. What are Branched Chain Alkanes
4. Side by Side Comparison – Straight vs Branched Chain Alkanes in Tabular Form
5. Summary
What are Straight Chain Alkanes?
Straight chain alkanes are hydrocarbon compounds containing a continuous chain of carbon atoms attached with hydrogen atoms. Alkanes are compounds containing only single bonds between carbon atoms. Straight chain alkanes are aliphatic because there are no ring structures or unsaturation in these compounds. Moreover, straight-chain alkanes are saturated compounds as there are no double or triple bonds between carbon atoms.
Figure 01: A Straight Chain Alkane Structure
The general molecular formula of these compounds follows the pattern CnH2n+2. There are no side chains or pendant groups attached to the continuous carbon chain of these molecules. When naming a straight chain alkane, we need to use a prefix that specifies the number of carbon atoms present in the molecule and the name ends with “-ane”, which indicates that it is an alkane. For example, the straight-chain alkane having five carbon atoms gets the name “pentane” (pent+ane).
What are Branched Chain Alkanes?
Branched chain alkanes are hydrocarbon compounds containing side groups attached to a continuous carbon chain. These side chains are named as branches. Therefore, these compounds are not linear hydrocarbons. Since they are alkanes, there are no double or triple bonds between carbon atoms. Hence, these molecules are saturated compounds. The branches present in these molecules include methyl, ethyl, propyl, etc.
When naming a branched-chain alkane, the nomenclature system is different than that of straight chain alkane nomenclature. Here, we have to indicate the names of the branches as well. The name of the continuous chain is called the stem name. When naming the branches, we have to use the suffix “–yl” instead of “-ane” along with the number of carbon atoms in the branch. For example, methyl, ethyl, etc. However, naming a large branched-chain alkane is much difficult. Therefore, it is important to remember the following steps;
- First, find the longest and continuous carbon chain (stem chain) and name it.
- Find the side chains and name them as well.
- Give numbers to each carbon atom in a way that side chains get the lowest number.
- Write the names of side chains in alphabetical order.
- Use a hyphen to separate the numbers of side chains from stem name.
- For example, a branched alkane having a methyl group at 2nd carbon of propane molecule gets the name “2-methylpropane”.
What is the Difference Between Straight and Branched Chain Alkanes?
Alkanes are hydrocarbon compounds with carbon and hydrogen atoms having only single bonds between them. Further, there are two types of alkanes as straight-chain alkanes and branched-chain alkanes. The key difference between straight and branched chain alkanes is that in straight-chain alkanes, all the carbon atoms bond with each other forming a continuous chain whereas branched chain alkanes have side chains attached to a continuous carbon chain.
Below infographic shows more details on the difference between straight and branched chain alkanes.
Summary – Straight vs Branched Chain Alkanes
Alkanes are hydrocarbon compounds containing carbon and hydrogen atoms having only single bonds between them. Based on their structure, there are two types of alkanes as straight-chain alkanes and branched-chain alkanes. The key difference between straight and branched chain alkanes is that in straight-chain alkanes, all the carbon atoms bond with each other forming a continuous chain whereas branched chain alkanes have side chains attached to a continuous carbon chain.
Reference:
1. Helmenstine, Anne Marie. “Branched Chain Alkane Definition.” ThoughtCo, Oct. 1, 2019, Available here.
Image Courtesy:
1. “Butan Lewis” By NEUROtiker ⇌ – Own work, Public Domain) via Commons Wikimedia
2. “IUPAC-alkane-1” By Fvasconcellos 20:04, 8 January 2008 (UTC). Original image by DrBob (talk · contribs). – Vector version of Image:Iupac-alkane-1.png by DrBob (talk · contribs) (CC BY-SA 3.0) via Commons Wikimedia