Difference Between Saturated and Unsaturated Hydrocarbons

Main Difference – Saturated vs Unsaturated Hydrocarbons

Hydrocarbons are organic compounds that contain only carbon and hydrogen atoms. Hydrocarbons are considered as parent compounds of many organic compounds. The main chain of hydrocarbons is made by the C-C bonds, and hydrogen atoms are attached to carbon atoms in the main chain. Based on the presence of single or multiple bonds between carbon atoms, hydrocarbons are classified into two groups namely; saturated hydrocarbons and unsaturated hydrocarbons. The main difference between saturated and unsaturated hydrocarbon is that saturated hydrocarbons contain only single covalent bonds between carbon atoms, whereas unsaturated hydrocarbons contain at least one double or triple covalent bond in the main chain. Saturated and unsaturated hydrocarbons show different characteristics because of these structural differences.

Key Areas Covered

1. What are Saturated Hydrocarbons
      – Definition, Structure, Types, Properties
2. What are Unsaturated Hydrocarbons
      – Definition, Structure, Types, Properties
3. What is the difference between Saturated and Unsaturated Hydrocarbons
      – Comparison of Key Differences

Key Terms: Hydrocarbons, Saturated Hydrocarbons, Unsaturated Hydrocarbons, Covalent Bonds, Alkanes, Alkenes, Alkynes, Aromatic Hydrocarbons

What are Saturated Hydrocarbons

Hydrocarbons in which all carbon atoms are bonded to other atoms by single covalent bonds are called saturated hydrocarbons. Thus, saturated hydrocarbons do not contain any multiple bonds, including double or triple covalent bonds. In these compounds, each carbon atom is bonded directly to four other atoms. Hence, all carbon atoms are fully occupied by making four bonds. This is why these compounds are called saturated hydrocarbons. Saturated hydrocarbons are the simplest and the least polar organic natural products. Examples of saturated hydrocarbons include alkanes and cycloalkane families of hydrocarbons.

The simplest form of saturated hydrocarbons includes methane (CH₄), ethane (C₂H₆), propane (C₃H₈) etc. Saturated hydrocarbons burn and give a blue, non-sooty flame in air. Because of the flammability of saturated hydrocarbons that ultimately release a lot of energy, saturated hydrocarbons are often used as a fuel source of vehicle and airplane engines. Well known LPG or cooking gas is also a saturated hydrocarbon called butane (C₄H₁₀). The combustion of alkanes with air will result in carbon dioxide gas, water vapor, heat, and light. Hydrocarbons are usually obtained from fossilized plant and animal matter. Once they are obtained as crude oil, the process called distillation is used to separate various products according to their mass. This whole process is called refining of crude oil.

Figure 1: Ethane

What are Unsaturated Hydrocarbons

Unsaturated hydrocarbons are the hydrocarbons that contain at least one carbon-carbon double or triple bond in their carbon chain or ring. These compounds have similar physical properties to those of saturated hydrocarbons. However, their chemical properties are much different from saturated hydrocarbons mainly due to the presence of multiple bonds. Usually, chemical reactions initiate from locations where multiple bonds are present in the carbon chain. Hence, the reactivity of unsaturated hydrocarbon increases with a number of multiple bonds present in the main chain.

Types of Unsaturated Hydrocarbons

There are three types of unsaturated hydrocarbons, namely; (a) alkenes, which contain one or more double bond (C=C), (b) alkynes, which contains one or more triple bonds (C≡C), and (c) aromatic hydrocarbons, which consist of a delocalized bonding resulting in a six-membered carbon ring. Examples of alkenes include ethene, propene, butene, etc. Acetylene, propyne, butyne are some examples for alkynes. Benzene, toluene, aniline are some common examples of aromatic hydrocarbons. The simplest form of unsaturated hydrocarbon is ethylene, which is important as a plant hormone that triggers the ripening of fruits.

Main Difference - Saturated vs Unsaturated Hydrocarbons

Figure 2: Some Alkynes

Definition

Saturated Hydrocarbons: Saturated hydrocarbons are hydrocarbons with only single covalent bonds.

Unsaturated Hydrocarbons: Unsaturated hydrocarbons are hydrocarbons with multiple covalent bonds (double and triple bonds).

Types

Saturated Hydrocarbons: Alkanes are saturated hydrocarbons.

Unsaturated Hydrocarbons: Alkenes, alkynes, and aromatic hydrocarbons are types of unsaturated hydrocarbons.

Reactivity

Saturated Hydrocarbons: Saturated hydrocarbons are less reactive.

Unsaturated Hydrocarbons: Unsaturated hydrocarbons are more reactive.

Burn in air

Saturated Hydrocarbons: Burning saturated hydrocarbons result in a blue, non-sooty flame.

Unsaturated Hydrocarbons: Burning unsaturated hydrocarbons result in a yellow, sooty flame.

Amount of Carbon and Hydrogen

Saturated Hydrocarbons: Saturated hydrocarbons have a less amount of carbon and high amount of hydrogen.

Unsaturated Hydrocarbons: Unsaturated hydrocarbons have a high amount of carbon and less amount of hydrogen

Sources

Saturated Hydrocarbons: These are usually obtained from fossilized plant and animal materials.

Unsaturated Hydrocarbons: These are mainly obtained from plants (plant pigments, waxes, proteins, vegetable oils etc.)

Conclusion

The difference between saturated and unsaturated hydrocarbons depends on the types of bonds they contain. Saturated hydrocarbons contain only single covalent bonds whereas unsaturated hydrocarbons contain at least one or more double or triple carbon-carbon bond. Hence, unsaturated hydrocarbons are more reactive than saturated hydrocarbons. Saturated hydrocarbons include the alkanes, whereas unsaturated hydrocarbons include alkene, alkynes and aromatic hydrocarbons.

References:
1. Cseke, Leland J., Ara Kirakosyan, Peter B. Kaufman, Sara Warber, James A. Duke, and Harry L. Brielmann. Natural products from plants. Boca Raton, FL: CRC Press, 2006. Print
2. Singh, Lakmir, and Manjit Kaur. Science for Tenth Class Part 2 Physics. N.p.: S. Chand, 2016. Print.
3. Stoker, H. Stephen. General, organic, and biological chemistry. 6th ed. N.p.: Cengage Learning, 2012. Print.

Image Courtesy:
1. “Ethane-2D” (Public Domain) via Commons Wikimedia
2. “Alkyne General Formulae V” By Jü – Own work (CC0) via Commons Wikimedia