Carboxyl Functional Group

Core Concepts

In this tutorial, you will learn about the carboxyl functional group and its properties. You will also learn about several examples of carboxyl’s and how it correlates to other functional groups.

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What is a Carboxyl Functional Group?

A carboxyl is a common functional group in organic chemistry. It can be referred to as a carboxy group, a carboxyl functional group, or a carboxyl radical. A carboxyl group consists of a carbon double-bonded to oxygen and singly bonded to a hydroxyl group. As a result, the formula for a carboxyl group is R-COOH where R is the organic compound chain.

carboxyl group structure
Carboxyl Functional Group Structure

It is important to note that an organic compound that consists of a carboxyl group is called carboxylic acid. These can include acetic acids and amino acids (which contain an amine group and a carboxyl group).

Carbonyl vs. Carboxyl Functional Groups

A carbonyl group and a carboxyl group are functional groups found in organic chemistry. A carbonyl consists of carbon atoms double bonded to an oxygen atom. These can be aldehydes and ketones. However, a carboxyl group has a different structure where the carbon atom is double bonded to oxygen and bonded to a hydroxyl group (-OH). The main difference between a carbonyl and a carboxyl is what their central carbon is bonded to.

Carboxyl functional group
Carboxyl Group
carbonyl group
Carbonyl Group

A carbonyl group has polarity due to the charge separation between the oxygen and carbon atoms, while a carboxyl has polarity in its carbonyl group. A carboxyl can release protons from its hydroxyl group, while a carbonyl group cannot.

Properties of a Carboxyl Functional Group

Carboxyl groups can ionize by releasing the hydrogen atom (proton) from their “-OH” group. As a result of the double-bonded oxygen (electronegative atom) to a carbon molecule, the polarity of the bond increases. Any compound that contains a carboxyl group will have hydrophilic (water repelling) centers, resulting in a high melting point and boiling point. These high melting and boiling points dissipate by allowing hydrogen to bond in a solid or liquid state, a common example would be fatty acids.

Carboxyl Functional Group Naming

It is important to note that a carboxyl group does not have specific naming rules. However, naming occurs based on what compound the carboxyl group is in. Since the carboxyl functional group can be found in carboxylic acids, their naming follows the rules for carboxylic acids. Carboxylic acids take the end of the parent’s name and substitute it with “oic acid”. The same applies when a carboxyl is in amino acids, naming follows the rules for amino acids.

Examples of Carboxyl’s

The most common example of a molecule that contains a carboxyl group would be a carboxylic acid. These molecules are in an abundance in nature. Some basic examples are listed below.

Acetic acid is the most simple structure that contains a carboxyl group.
Acetic Acid Structure

Acetic acid has a distinctive pungent odor and sour flavor. It is often used as a solvent and found in kitchen vinegar.

Citric acid
Citric Acid

Citric acid is common in food preservatives and flavoring additives. This molecule exists naturally in citrus fruits and manufactured.

Another compound that contains a carboxyl group would be amino acids. What makes amino acids unique is that they contain a carboxyl group and an amino group. Down below are two examples of amino acids.

Glycine is an amino acid that contains a carboxyl functional group
Lysine formula, an amino acid that contains a carboxyl functional group.

Both of these amino acids contain a carboxyl group and build proteins within our bodies. It is important to note that the carboxyl functional group is important in composing much larger molecules that are found within our bodies or nature.

Further Reading