Organic Chemistry Tutorials

Functional Groups in Organic Chemistry

functional groups chemistry

Core Concepts

In this tutorial, you will learn what exactly functional groups are and why they are important in organic chemistry. You will also learn how to easily identify the different classes of functional groups in organic compounds in order to assist with your problem-solving.

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What are Functional Groups?

A functional group is a specific group of atoms with distinct properties and reactivity. Regardless of the other atoms present, functional groups will lend identical properties to their parent molecules. For example, this means that an alcohol will act the same way no matter if it’s part of methyl-alcohol, ethyl-alcohol, or isopropyl-alcohol.

Additionally, these functional groups will often serve as the primary acidic or basic sites in a compound; this makes them more prone to be a reaction site for different organic reactions.

While unfamiliar organic molecules may seem daunting, learning to identify functional groups will greatly assist in breaking down any compound into its core properties and potential reactions. Let’s go through them below!

Categories of Functional Groups

In order to make them simpler to recognize and remember, we can categorize different functional groups together based on their structural properties.

* In each diagram below, “R” refers to the rest of the organic molecule. If a single compound has different side chains, it will be signified by R, R’, R*, etc.


Hydrocarbons are solely made up of carbon and hydrogen atoms. The hydrocarbon functional groups are alkanes, alkenes, alkynes, and aromatic hydrocarbons (arenes).

hydrocarbon functional groups

Oxygen-Containing Functional Groups

Groups containing oxygen may have a carbonyl (carbon-oxygen double bond) or not. The functional groups without carbonyls are ethers, alcohols, and epoxides. Functional groups with carbonyls are aldehydes, ketones, carboxylic acids, and carboxylic acid derivatives.

The carboxylic acid derivatives are distinct functional groups that contain both a carbonyl and an additional acyl group. Esters, anhydrides, acyl halides (which also contain halogens), and amides (which also contain nitrogen) are all carboxylic acid derivatives. Esters can be formed via a process called esterification.

oxygen-containing functional groups

Nitrogen-Containing Functional Groups

The primary functional groups containing nitrogen are amino, amines, amides, and nitriles. Other groups, such as imines, azos, and azides are important, although come up less frequently.

nitrogen-containing functional groups

Sulfur-Containing Functional Groups

Thiols, thioethers, and disulfides are the most common functional groups with sulfur. An easy way to remember the functional groups with sulfur is to notice the similarities between the sulfur and oxygen groups. For instance, replace the oxygen in an alcohol to get a thiol; or, replace the oxygen in an ether to get a thiother.

sulfur groups

Halogen-Containing Functional Groups

Alkyl halides and acyl halides are the only true functional groups with halogens. They are easily recognizable because they will contain a single F, Cl, Br, or I atom singled-bonded to a carbon

halogen groups organic chemistry
X = F, Cl, Br, or I

Functional Groups in a Larger Compound

Now that we have established the main functional groups that you’re likely to come across in organic chemistry, it’s time to use that to your advantage. Since most organic molecules are constructed from carbon and hydrogen, the easiest way to spot a functional group is to look for any distinct atom (i.e oxygen, nitrogen, sulfur, or halogens). From there, consult the corresponding category from the list above. Let’s take a look at the example below:

functional group example problem

The first thing to do is to notice both of the oxygen atoms. One of them is part of a carbonyl, and the other is part of the acyl group.

Look towards the category of oxygen-containing functional groups to start limiting options. The only groups that fit the initial parameters are carboxylic acids and esters.

This molecule cannot contain a carboxylic acid because there is no oxygen-hydrogen alcohol group bonded to the carbonyl. But if you look at the ester functional group, you will see that this molecule matches perfectly. There is a carbonyl, with an oxygen-carbon acyl group.

Looking at the properties of an ester will tell you how the compound will behave. All you had to do is find the functional group!

Further Reading

See the topics below for some in-depth reading into the specific properties of the individual functional groups:

  • Alkenes, Alkanes, Alkynes, and Arenes
  • Aldehydes, Ketones, Carboxylic Acids, and Carboxylic Acid Derivatives
  • Alcohols, Epoxides, and Ethers
  • Thiols and Thioethers
  • Alkyl Halides and Acyl Halides

Once you master functional groups, you can learn more about organic chemistry topics by starting with topics:

One thought on “Functional Groups in Organic Chemistry

  1. Noa Spero says:

    Wow this is incredible. I learned so much from this article so thank you to the entire ChemTalk team for making my study of orgo easier! I love functional groups now! And that article on iron was also perfect for my periodic table presentation. Thanks for all you hardwork!

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