Saturated Bond

How often have you read a food label and wondered what saturated fats are? Fats differ according to whether they contain single or double bonds in their structure! Compounds in Organic Chemistry are also divided into saturated and unsaturated compounds according to their bonds!

So, without further ado, let's dive into unsaturated and saturated bonds!

• First, we will talk about saturated and unsaturated Carbon compounds.
• Next, we will learn about the structure of saturated bonds.
• After, we will look at the definition of unsaturated bonds and their reactivity.
• Then, we will talk about the catalytic hydrogenation of Alkenes and alkynes into Alkanes.
• Lastly, we will look at the basics of degree of unsaturation (IHD) and how to use it to find out how many hydrogens are missing in a compound.

Saturated and Unsaturated Carbon Compounds

Before diving into saturated and unsaturated bonds, let's review what Carbon compounds are. Carbon compounds are compounds that contain carbon and at least one other element, such as hydrogen, oxygen, Nitrogen, and sulfur.

Figure 1 shows some examples of carbon compounds.

Now, If you look carefully at the carbon compounds above, what do you notice about them? If you said that some of them have single bonds while others have double bonds, then you are on the right track! A carbon (C) atom is able to form single (C–C), double (C=C), and even triple bonds (C≡C)!

When an organic compound possesses the maximum number of single bonds to carbon, and no double or triple bonds, we call it a saturated bond.

Saturated Bond Structure

As an example, let's look at the saturated bond structure of methane, CH₄. Here, notice that the carbon atom is surrounded by four single covalent bonds to hydrogen, making it a saturated hydrocarbon. Carbon compounds containing only carbon and hydrogen atoms (such as CH₄) are called hydrocarbons, and they are the simplest form of carbon compounds!

Hydrocarbons with saturated bonds are called Alkanes, and they have the general formula C_nH_2n+2. For example, if we had an alkane with 3 carbon atoms, its general formula would be C₃H₈. The saturated bond structure of propane (C₃H₈) is shown below. The condensed formula for propane is CH₃CH₂CH₃.

Unsaturated Bond Definition

Next, we have unsaturated bonds. Unsaturated hydrocarbons can be Alkenes and have the general formula C_nH_2n, or alkynes, with the general formula C_nH_2n-2.

Ethene (C₂H₄) and ethyne (C₂H₂) are both examples of carbon compounds containing unsaturated bonds (Figure 4). Ethene is the simplest alkene in Organic Chemistry, and it has a double bond between the two carbon atoms. On the other hand, ethyne is the simplest alkyne, and it has a triple bond between the two carbon atoms.

Let's look at an example!

Another organic compound that is considered unsaturated is the aromatic compound. Aromatic compounds include carbon compounds that have a benzene ring (six-membered ring) containing double bonds.

Unsaturated Bond

Let's take a moment to talk about orbitals in chemical bonds.

Now that we know what saturated, and unsaturated bonds are, let's talk about their reactivity. But first, remember that single bonds are only made up of sigma (σ) bonds, whereas double and triple bonds contain both sigma (σ) and pi (π) bonds. Water (H₂O), for example, has only single, sigma bonds!

Let's look at an example.

The presence of these pi (π) bonds in alkenes and alkynes make them more chemically reactive than alkanes because π bonds are easier to break, allowing each carbon atom to become an active site that can form a new Covalent Bond with another atom (one pi bond turns into 2 sigma bonds).

Double Saturated Bond

When talking about unsaturated and saturated bonds, there is a technique called catalytic hydrogenation, which can be used to saturate a double bond! The process of catalytic hydrogenation of ethene (C₂H₄) into ethane (C₂H₆) can be seen in Figure 9, below.

First, ethene attaches to a metal catalyst surface covered with hydrogen atoms. Then, double bond between the two carbon atoms gets broken and the hydrogen atoms covalently bond to the carbon atoms. This addition of two hydrogen atoms produces a saturated alkane (ethane).

Hydrogenation can also be used to convert an alkyne into an alkane. For example, the addition of hydrogen gas to ethyne turns it into ethane!

Saturated vs. Unsaturated Bond

Let's continue learning about unsaturated and saturated bonds by looking at the degree of unsaturation (IHD) of hydrocarbons. The degree of unsaturation (IHD) rules helps us quickly determine which molecule is more saturated/less saturated with hydrogen.

• Having 1 IHD is the equivalent of that compound missing 2 hydrogens.

• Rings or double bonds count as 1 IHD

• Triple bonds count as 2 IHD

Let's look at an example.

Saturated and Unsaturated Bonds Difference

To finish off, let's make a table to review the difference between saturated and unsaturated bonds.

Now, I hope that you were able to gain a better understanding of what unsaturated and saturated bonds are!