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 groups in organic compounds in order to assist with your problem-solving.
Topics Covered In Other Articles
- Acids and Bases
- Formal Charge
- Resonance
- Cycloalkanes
- Acid Base Properties
What are Functional Groups?
A functional group is a specific group of atoms with distinct properties and reactivity. Within a molecule, functional groups shape the compound’s chemical behavior.
Regardless of the other atoms present, these groups will lend the same properties to their parent structures. For example, this means that an alcohol will act similarly no matter if it’s part of methyl-alcohol, ethyl-alcohol, or isopropyl-alcohol. The alcohol functional group (a carbon atom bonded to a hydroxyl group) is responsible for the unique traits of alcohols, such as their solubility in water and their ability to form hydrogen bonds.
Additionally, these groups serve as the primary acidic or basic sites in a compound; this makes them more prone to be a site for organic reactions.
Understanding functional groups is crucial for understanding organic chemistry, which is the study of carbon-based molecules. While unfamiliar organic molecules may seem daunting, learning to pick out these groups will greatly help 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 groups together based on their structural traits.
In each diagram, “R” refers to some unimportant side chain. If a compound has different side chains, then it will be signified by R, R’, R*, etc.
Hydrocarbons
Hydrocarbons are solely made up of carbon and hydrogen atoms. The hydrocarbon groups are alkanes, alkenes, alkynes, and aromatic hydrocarbons (arenes).
Oxygen-Containing Functional Groups
Groups with oxygen may have a carbonyl (carbon-oxygen double bond) or not. The functional groups without carbonyls are ethers, alcohols, and epoxides. Conversely, these groups with carbonyls are aldehydes, ketones, carboxylic acids, and carboxylic acid derivatives.
The carboxylic acid derivatives are distinct groups that have both a carbonyl as well as an acyl group. Esters, anhydrides, acyl halides (which also have halogens), and amides (which also have nitrogen) are all carboxylic acid derivatives. Esters can form through the process of esterification.
Nitrogen-Containing Functional Groups
The main groups with nitrogen are amines, amides, and nitriles. Other groups, such as imines, azos, and azides are important but come up less.
Sulfur-Containing Functional Groups
Thiols, thioethers, and disulfides are the most common functional groups with sulfur. To remember the sulfur groups, notice the similarities between the sulfur and oxygen groups. For instance, change the oxygen in an alcohol to get a thiol; or, change the oxygen in an ether to then get a thiother.
Halogen-Containing Functional Groups
Alkyl halides and acyl halides are the only true functional groups with halogens. They are easily noticed because they will have a single F, Cl, Br, or I atom singled-bonded to a carbon
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 put that to use. Since most organic compounds are made mostly from carbon and hydrogen, the easy way to spot a group is to look for any distinct atom (i.e oxygen, nitrogen, sulfur, or halogens). Then, check the categories from the list above. Let’s take a look at the example below:
Firstly, notice both of the oxygen atoms. One of them is part of a carbonyl while the other is part of the acyl group.
Secondly, look towards the category of oxygen-containing groups to limit our options. The only groups that fit the initial traits are carboxylic acids and esters.
This molecule cannot have a carboxylic acid because it lacks a oxygen-hydrogen alcohol group bonded to the carbonyl. But if you look at the ester group, you will see that this structure matches perfectly. There is a carbonyl, with an oxygen-carbon acyl group.
Looking at the traits of an ester will then tell you how the compound will behave. All you had to do is find the functional group!
List of Common Functional Groups
- Alcohols (e.g. ethanol)
- Aldehydes (e.g. formaldehyde)
- Ketones (e.g. acetone)
- Carboxylic acids (e.g. acetic acid)
- Esters (e.g. ethyl acetate)
- Amides (e.g. acetamide)
- Amines (e.g. ethylamine)
- Halides (e.g. alkyl halides)
- Ethers (e.g. diethyl ether)
- Alkenes (e.g. ethene)
- Alkynes (e.g. acetylene)
Many of these functional groups are linked below to entire pages about their structure and properties!
List of Less Common Functional Groups
- Nitriles
- Dienes
- Epoxides
- Sulfoxides
- Sulfones
- Sulfonamides
- Nitro compounds
- Thiols
- Disulfides
- Thioethers
- Imides
- Nitroso compounds
- Isocyanates
- Isothiocyanates
- Thiocarbamates
- Thioureas
- Dithiocarbamates
Further Reading
See the links below for some in-depth reading on the unique properties of each group:
- Alkenes, Alkanes, Alkynes, and Arenes
- Aldehydes, Ketones, Carboxylic Acids, and Carboxylic Acid Derivatives
- Alcohols, Epoxides, Amines, 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:
- What is a Nucleophile?
- What is a Electrophile?
- Stereoisomers and Chiral Centers
- Leaving groups
- Carbocation Stability
- What is structural isomerism?
- Spectral Analysis of Organic Compounds
- What are Protecting Groups
