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Naming Aldehydes & Ketones Using IUPAC Nomenclature

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

This lesson will help you understand the IUPAC naming rules for aldehydes and ketones. We'll review what these molecules are, then look at naming conventions and go over some examples.

What Are Aldehydes and Ketones?

Picture waiting for the subway on a hot, summer day. Everyone is drenched in sweat in their dress clothes, waiting for the five o'clock train home in the summer heat. If you've ever experienced this you know the platform won't smell too good either. But, what you might not know is that a ketone called butanedione is responsible for the smell.

Butanedione is an example of a ketone
Butanedione

When we sweat, bacteria break down normally neutral compounds into smelly ones, like butanedione. Fortunately, not all ketones are so smelly. Ketones are found in steroid hormones, medicine, and types of metabolic byproducts in our body. They are also used in the manufacturing industry to make lacquers, paints and textiles.

Ketones are often discussed in conjunction with aldehydes because both are defined by a carbonyl group, or a functional group consisting of a carbon bound to an oxygen atom through a double, covalent bond.

Aldehydes and ketones are different because aldehydes are bound to a carbon that is attached to one other group and a hydrogen, whereas ketones are bound to a carbon that is attached to two additional groups, but no hydrogens.

General structure of a ketone
ketone

Aldehydes are also used in some medicinal products, such as pharmaceuticals, and they are commonly found in perfumes, dyes and textiles. Aldehydes often have a sweet odor associated with them.

General structure of an aldehyde
aldehyde

IUPAC Naming Rules

Now that we know what ketones and aldehydes are, let's examine how to name them according to the the International Union of Pure and Applied Chemistry (IUPAC) naming rules.

1. Determine the longest carbon chain that contains the aldehyde or ketone group. You can do this by counting the carbons - either by looking for the letter 'C' or by counting the intersections if the structure is drawn as connected lines. Use the table below to name the base alkane:

Number of
Carbons
Name
1 Methane
2 Ethane
3 Propane
4 Butane
5 Pentane
6 Hexane
7 Heptane
8 Octane
9 Nonane
10 Decane

2. Now, for aldehydes, change the 'e' ending on the alkane name to ''al'. For ketones, change the 'e' ending to 'one'.

3. Add in a prefix to identify where the aldehyde or ketone is on the carbon chain. To do this, count the carbons in the parent alkane by finding the numbering that gives the aldehyde or ketone the lowest number.

4. Add in any substituents by adding the number carbon they are attached to with their prefix from the chart above. Substituents may be a methyl group or other alkyl group. List all substituents in alphabetical order prior to naming the aldehyde or ketone.

Examples

Let's look at some examples of how to name aldehydes and ketones using the steps above.

Aldehydes

To start, let's look an at aldehyde with a substituent group off of the parent carbon chain.

An example of an aldehyde with substituents
aldehyde example

First count the carbons. Each angle or branch in the line is one carbon, so this chain has four carbons and thus the parent carbon chain name is butane.

Now let's number the carbons so that the aldehyde group has the lowest number. We'll start from right to left. Now, we can see that the methyl substituent group has a position of two, so we will include the number two prior to it's name.

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