Difference Between Saturated and Unsaturated Compounds

Main Difference – Saturated vs Unsaturated Compounds

In organic chemistry, a chemical compound can be either saturated or unsaturated based on the type of chemical bonding between carbon atoms. These terms are to describe alkanes, alkenes, and alkynes. A saturated compound is only composed of carbon-carbon single bonds. For example, alkanes are composed of C-C single bonds. Unsaturated compounds can have double bonds and triple bonds as well. For example, alkenes contain double bonds and alkynes contain triple bonds. Therefore the main difference between saturated and unsaturated compounds is that saturated compounds have only carbon-carbon single bonds whereas unsaturated compounds have carbon-carbon double bonds and triple bonds.

Key Areas Covered

1. What are Saturated Compounds
     – Definition, Explanation with Examples
2. What are Unsaturated Compounds
     – Definition, Explanation with Examples
3. What is the Difference Between Saturated and Unsaturated Compounds
     – Comparison of Key Differences

Key Terms: Alkane, Alkene, Alkyne, Aromatic, Fatty Acids, Hybridization, Saturated Compounds, Unsaturated Compounds

What are Saturated Compounds

Saturated compounds are organic compounds that have only carbon-carbon single bonds. Aliphatic alkanes and cycloalkanes are saturated compounds. These compounds can be straight chains, can have side groups, and can be branched structures or cyclic structures, but without double bonds or triple bonds.

Saturated compounds are very unreactive and more stable than unsaturated compounds. These compounds have low melting points and boiling points relative to their molar mass. All carbon atoms in C-C bonds are sp³ hybridized atoms in saturated compounds. The simplest alkane is methane. It has one carbon atom bonded to four carbon atoms. There are no double bonds or triple bonds between atoms. The simplest cycloalkane is cyclopropane. It has three carbon atoms bonded to each other, forming a ring structure. Each carbon atom is bonded to two hydrogen atoms; hence there are no double bonds or triple bonds in this structure as well.

Figure 1: Chemical Structure is Cyclopropane

In saturated compounds, more hydrogen atoms are bonded to carbon atoms when compared to unsaturated compounds having the same number of carbon atoms. Apart from alkanes, there can be alcohols such as butanol having only C-C bonds and one C-OH bond. But no unsaturation is present. Saturated fatty acids are also considered as saturated compounds when compared to unsaturated fatty acids. Saturated fatty acids have saturated fatty acid chains that have no double bonds or triple bonds.

What are Unsaturated Compounds

Unsaturated compounds are organic compounds containing at least one double bond or a triple bond between the carbon atoms. These bonds can be either conjugated or not. Conjugated refers to the presence of chemical bonds in a compound that are reversibly combined with another. The major unsaturated compounds are alkenes, alkynes, and aromatic compounds.

Alkenes are organic compounds having at least one double bond. A double bond consists of a sigma bond and a pi bond. A sigma bond is a type of chemical bond that is formed due to the head-on overlapping between atomic orbitals. A pi bond is formed due to overlapping of p orbitals. The carbon atoms having double bonds in alkene are sp² hybridized.  

Alkynes are compounds that are composed of at least one triple bond. A triple bond is composed of a sigma bond and two pi bonds. The carbon atoms having triple bonds in alkynes are sp hybridized. An aromatic compound is an unsaturated compound composed of double bonds and single bonds that are arranged in an alternating pattern.

Figure 2: Alkynes have Triple Bonds

Unsaturated compounds are very reactive due to the presence of double bonds and triple bonds. The hydrogen atoms per carbon atom are less than that in saturated compounds. Therefore they are unstable. Unsaturated compounds are able to undergo polymerization. The polymerization of unsaturated compounds makes saturated polymers.

Difference Between Saturated and Unsaturated Compounds

Definition

Saturated Compounds: Saturated compounds are organic compounds that have only carbon-carbon single bonds.

Unsaturated Compounds: Unsaturated compounds are organic compounds containing at least one double bond or triple bond between carbon atoms.

Chemical Bonding

Saturated Compounds: Saturated compounds have only single bonds between carbon atoms.

Unsaturated Compounds: Unsaturated compounds have at least one double bond or triple bond between two carbon atoms.

Pi Bonds

Saturated Compounds: Saturated compounds have no pi bonds between carbon atoms.

Unsaturated Compounds: Unsaturated compounds have pi bonds between carbon atoms; one pi bonds in alkenes, two pi bonds in alkynes.

Reactivity

Saturated Compounds: Saturated compounds are less reactive.

Unsaturated Compounds: Unsaturated compounds are highly reactive.

Hybridization

Saturated Compounds: The carbon atoms in saturated compounds are sp³ hybridized.

Unsaturated Compounds: The carbon atoms in unsaturated compounds are either sp² or sp³ hybridized (carbon atoms having double bonds and triple bonds respectively).

Hydrogen Atoms per Molecule

Saturated Compounds: Saturated compounds have more hydrogen atoms per carbon.

Unsaturated Compounds: Unsaturated compounds have less number of hydrogen atoms per carbon atom when compared to saturated compounds.

Polymerization

Saturated Compounds: Saturated compounds do not undergo polymerization.

Unsaturated Compounds: Unsaturated compounds undergo polymerization.

Stability

Saturated Compounds: Saturated compounds are more stable.

Unsaturated Compounds: Unsaturated compounds are less stable.

Examples

Saturated Compounds: Saturated compounds include alkanes and cycloalkanes.

Unsaturated Compounds: Unsaturated compounds include alkenes, alkynes, and aromatic compounds.

Conclusion

Organic compounds can be saturated or unsaturated based on their chemical bonding. Saturated compounds are stable than unsaturated compounds. The main difference between saturated and unsaturated compounds is that saturated compounds have only carbon-carbon single bonds whereas unsaturated have carbon-carbon double bonds and triple bonds.

Reference:

1. “Saturated vs. Unsaturated Hydrocarbons.” Soft School, Available here.
2. “Structure and Nomenclature of Hydrocarbons.” Purdue, Available here.

Image Courtesy:

1. “Cyclopropane-2D” (Public Domain) via Commons Wikimedia
2. “IUPAC-alkyne” By Fvasconcellos 20:06, 8 January 2008 (UTC). Original image by DrBob (talk · contribs). – Vector version of en:Image:Iupac-alkyne.png by DrBob (talk · contribs) (CC BY-SA 3.0) via Commons Wikimedia