IUPAC Naming of Organic Compounds | ChemTalk (2024)

Core Concepts

In this tutorial, you will learn all about the IUPAC naming of organic compounds. This includes an introduction to the IUPAC system of nomenclature, the steps to follow when naming an organic compound, and some practice examples.

Topics Covered in Other Articles

• Naming Alkanes
• Naming Cyclohexanes
• Functional Groups in Organic Chemistry
• Constitutional Isomers
• Relative configuration

Introduction to IUPAC Nomenclature

The IUPAC system of nomenclature is a universally-recognized method for naming organic chemical compounds. The goal of the system is to provide each organic compound with a unique and unambiguous name based on its chemical formula and structure.

The name of any organic compound consists of three essential parts: the root word, prefix, and suffix.

• Root Word: The root word indicates the number of carbon atoms present in a compound’s parent chain.
• Prefix: A prefix appears before the root word and denotes substituents (i.e., functional groups or atoms other than hydrogen) attached to the parent chain.
• Suffix: The end of the name can include both primary and secondary suffixes. The primary suffix indicates the degree of saturation (based on the presence or absence of a multiple bond). The secondary suffix, on the other hand, represents a compound’s principal characteristic group. All organic compounds contain a primary suffix; however, not all compounds contain a secondary suffix.

In addition, many organic compounds contain locants, which are numbers that identify the location of functional groups on the parent chain. A locant may be used before prefixes, primary suffixes, and secondary suffixes in a compound’s IUPAC name.

Steps for Naming Organic Compounds

Naming an unfamiliar organic compound using the IUPAC system can be quite difficult. However, the process becomes much easier if you just follow these 8 key steps.

Step 1: Determine the Principal Characteristic Group

The first step is to determine the principal characteristic group (i.e., the highest priority functional group) contained in the compound of interest. Completing this step will allow you to determine the compound’s secondary suffix (if applicable). The chart below lists functional groups in order from highest to lowest priority and includes their secondary suffix as well.

Functional Group	Secondary Suffix
1. Carboxylic Acid	-carboxylic acid -oic acid
2. Sulfonic Acid	-sulfonic acid
3. Ester	-oate
4. Acid Halide	-oyl halide (-oyl fluoride, -oyl chloride, -oyl bromide, -oyl iodide)
5. Amide	-carboxamide -amide
6. Nitrile	-nitrile
7. Aldehyde	-carbaldehyde -al
8. Ketone	-one
9. Alcohol	-ol
10. Thiol	-thiol
11. Amine	-amine

It is important to note that the presence of alkenes, alkynes, alkyl groups, alkoxy groups, or halogens in an organic compound does not result in the use of a secondary suffix; therefore, the list above does not include these functional groups. Furthermore, this list is not comprehensive but does include the most commonly encountered functional groups that require a secondary suffix (if designated as the highest priority).

If the principal characteristic group appears more than once in the compound, then you will need to alter the secondary suffix by adding the appropriate multiplying affix (“di,-” “tri-,” “tetra-,” etc.). For example, a compound with two carboxyl groups would use the secondary suffix “-dioic acid.” Shown below is a table listing the multiplying affixes used by the IUPAC system of nomenclature for repeated functional groups in an organic compound.

Step 2: Identify the Parent Chain

In general, a parent chain is the longest, uninterrupted chain of carbon atoms in a given compound. Quite often, this definition holds true; however, there is one major exception. If a compound contains a principal characteristic group (requiring a secondary suffix), then it must be included in the parent chain. For example, two potential parent chains (Option A and Option B) are numbered and shown below. Although Option B is longer and contains more carbon atoms, Option A is the preferred parent chain for IUPAC naming because it is directly bonded to the hydroxyl group.

Furthermore, if two potential parent chains are equal in length, you will want to choose the option with the greatest number of double/triple bonds (if applicable) or the greatest number of substituents. The two examples shown below demonstrate the application of these criteria when determining the parent chain.

It is also important to note that parent chains can be cyclic (i.e., in the form of a ring). In these cases, “cyclo” precedes the root word in the IUPAC name.

Step 3: Choose the Appropriate Root Word

Once you have identified the parent chain, you can then determine the appropriate root word based on the number of consecutive carbon atoms it contains. The chart below shows the root words to use for organic compounds with parent chains containing between 1-10 carbon atoms.

Step 4: Identify Any Double or Triple Bonds

The presence (or absence) of double/triple bonds between carbon atoms in the parent chain will determine the organic compound’s primary suffix. Alkanes contain only single bonds between carbon atoms and use the primary suffix “-ane.” Alkenes contain at least one carbon-carbon double bond and use the primary suffix “-ene.” Lastly, alkynes contain at least one carbon-carbon triple bond and use the primary suffix “-yne.”

A compound’s primary suffix slightly changes if it contains a principal characteristic group that uses a secondary suffix beginning with a vowel. In these cases, the final letter “e” is dropped from the primary suffix. For example, the compound shown below includes a hydroxyl group that requires the secondary suffix “-ol.” As a result, it is named ethanol (not “ethaneol”).

If an alkene contains multiple double bonds, then the primary suffix would become “-adiene” (for 2 double bonds), “-atriene” (for 3 double bonds), “-atetraene” (for 4 double bonds), and so on. Alkynes work the same way; the presence of multiple triple bonds would cause the primary suffix to become “-adiyne,” “atriyne,” “atetrayne,” etc. Furthermore, if an organic compound contains both a double bond and a triple bond, you would use two primary suffixes in its name: “en” to represent the double bond and “yne” to represent the triple bond (with “en” preceding “yne” in the IUPAC name).

Step 5: Identify Any Side Chains or Lower Priority Functional Groups

Any substituent attached to the parent chain must be identified in the IUPAC name by using the appropriate prefix. This includes carbon side chains known as alkyl groups, which are named similarly to alkanes. Simple, unbranched alkyl groups contain a root word based on their number of carbon atoms (meth, eth, prop, but, etc.) and the ending “-yl” in their names. However, the naming of branched alkyl groups is more complex and described in further detail here. Some examples of alkyl groups (along with both their common and IUPAC names) are depicted in the chart below.

Alkyl Group (R-)	Common Name	IUPAC Name
	Methyl	Methyl
	Ethyl	Ethyl
	Propyl	Propyl
	Isopropyl	(1-methylethyl)
	Butyl	Butyl
	Isobutyl	(2-methylpropyl)
	Sec-butyl (or s-butyl)	(1-methylpropyl)
	Tert-butyl (or t-butyl)	(1,1-dimethylethyl)

In addition, any functional groups attached to the parent chain (other than the principal characteristic group) are named using their designated prefixes. The chart below shows some of the most common functional groups (listed in alphabetical order) and their prefixes.

When a compound requires multiple prefixes, you should list them alphabetically at the beginning of the IUPAC name. In the example shown below, there are three substituents attached to the parent chain: a chlorine atom, methyl group, and bromine atom. As a result, their prefixes (“chloro-,” “methyl-,” and “bromo-“) are put in alphabetical order, resulting in the IUPAC name 4-bromo-2-chloro-3-methylhexane.

If a side chain or lower priority functional group appears more than once in a compound, then a multiplying affix (“di-,” “tri-,” “tetra-,” etc.) should be added to the prefix. For example, a compound containing 3 methyl groups will use the prefix “trimethyl-.”

Step 6: Number the Parent Chain

Numbering the parent chain allows you to determine the locant(s) used to identify any functional groups, side chains, or double/triple bonds contained in the compound. The parent chain should be numbered in such a way that the principal characteristic group has the lowest number possible.

If there is no principal characteristic group, then the parent chain should be numbered in the way that gives any double or triple bonds the lowest possible number.

If there is no principal characteristic group or double/triple bonds, then the parent chain should be numbered in the way that gives any other substituents (e.g., alkyl groups or halogens) the lowest possible number.

Compounds with multiple substituents or double/triple bonds follow the first point of difference rule. This rule states that you should start at each end of the parent chain and go term-by-term in both directions. When you reach the first substituent or multiple bond, it is given the lowest locant, and the numbering of the parent chain continues in that direction.

If you are still unable to choose the direction in which to number the parent chain, then you will want to choose the way that gives the lowest possible locant to the substituent that comes first in alphabetical order.

Step 7: Assign Stereochemistry

It is also important to designate the stereochemistry of any chiral centers or double bonds contained in the compound (if applicable). For chiral centers, this is done by assigning R or S configuration. For double bonds, stereochemistry is indicated by using the E/Z system. Stereodescriptors (e.g., R/S and E/Z) are typically written in parentheses at the beginning of the IUPAC name. If a compound contains multiple chiral centers or multiple double bonds, a locant must be placed before the stereodescriptor.

Step 8: Assemble the IUPAC Name

Now, it is time to use all the information gathered from the first six steps. You combine the prefix(es), root word, primary suffix, and secondary suffix (while also adding locants when necessary) to form the compound’s IUPAC name.

Examples of IUPAC Naming

Shown below are some examples of IUPAC naming using the 8-step process described in this article.

Example 1

Step 1: Determine the principal characteristic group.

The principal characteristic group is carboxylic acid (because carboxylic acids have priority over alcohols in IUPAC naming). Therefore, the secondary suffix will be “-oic acid.”

Step 2: Identify the parent chain.

Outlined in blue (in the image above) is the parent chain. It was chosen because it is the longest stretch of consecutive carbon atoms that contains the principal characteristic group.

Step 3: Choose the appropriate root word.

The parent chain contains 5 carbon atoms; therefore, it will use the root word “pent.”

Step 4: Identify any double or triple bonds.

The compound does not contain any double or triple bonds; therefore, it will use the primary suffix “-an.” The “e” is dropped from “-ane” because the secondary suffix (“-oic acid”) begins with a vowel.

Step 5: Identify any side chains or lower priority functional groups.

There are 3 other substituents attached to the parent chain: a methyl group, an ethyl group, and a hydroxyl group. Therefore, 3 prefixes are needed: “ethyl-,” “hydroxy-,” and “methyl-” (listed in alphabetical order).

Step 6: Number the parent chain.

Shown above is the numbering of the parent chain. This direction was chosen in order to give the principal characteristic group the lowest possible number.

You can also now determine the locants. The ethyl group attaches to the second carbon, the methyl group attaches to the third carbon, and the hydroxyl group attaches to the fourth carbon. It is not necessary to use a locant for the principal characteristic group (carboxylic acid) because the carboxyl group is always at the beginning of the parent chain.

Step 7: Assign stereochemistry.

There are no carbon-carbon double bonds; therefore, the E/Z naming system will not be used. In addition, although there are several chiral centers (at C2, C3, and C4), it is not possible to determine the stereochemistry due to the lack of wedge-and-dash notation; therefore, R or S configuration will not be assigned.

Step 8: Assemble the IUPAC name.

The IUPAC name of this compound is 2-ethyl-4-hydroxy-3-methylpentanoic acid.

Example 2

Step 1: Determine the principal characteristic group.

There is no principal characteristic group for this compound; therefore, it will not contain a secondary suffix.

Step 2: Identify the parent chain.

Outlined in red (in the image above) is the parent chain. It was chosen because it is the longest stretch of consecutive carbon atoms that contains both carbon-carbon double bonds.

Step 3: Choose the appropriate root word.

The parent chain contains 9 carbon atoms; therefore, it will use the root word “non.”

Step 4: Identify any double or triple bonds.

There are two double bonds present in the compound; therefore, it will use the primary suffix “-adiene.”

Step 5: Identify any side chains or lower priority functional groups.

There are 3 total substituents attached to the parent chain: 2 ethyl groups and a chlorine atom. Only 2 prefixes are needed: “chloro-” and “diethyl-” (listed in alphabetical order).

Step 6: Number the parent chain.

Shown above is the numbering of the parent chain. This direction chosen follows the first point of difference rule; in other words, it gives the first carbon-carbon double bond the lowest possible locant.

You can also now determine the locants. The first ethyl group attaches to the third carbon, the chlorine atom attaches to the fifth carbon, and the second ethyl group attaches to the sixth carbon. In addition, the two carbon-carbon double bonds begin at the second and sixth carbons.

Step 7: Assign stereochemistry.

The first carbon-carbon double bond (between C2 and C3) uses the stereodescriptor “E,” while the second carbon-carbon double bond (between C6 and C7) uses the stereodescriptor “Z.” Meanwhile, the chiral center at the fifth carbon uses the stereodescriptor “S.”

Step 8: Assemble the IUPAC name.

The IUPAC name of this compound is (2E,5S,6Z)-5-chloro-3,6-diethyl-2,6-nonadiene.

Example 3

Step 1: Determine the principal characteristic group.

The principal characteristic group is alcohol. Since there are two hydroxyl groups, the secondary suffix will be “-diol.”

Step 2: Identify the parent chain.

Outlined in green (in the image above) is the parent chain. It was chosen because it is the longest stretch of consecutive carbon atoms that contains the principal characteristic group, the carbon-carbon double bond, and the carbon-carbon triple bond.

Step 3: Choose the appropriate root word.

The parent chain contains 6 carbon atoms; therefore, it will use the root word “hex.”

Step 4: Identify any double or triple bonds.

The compound contains a carbon-carbon double bond and a carbon-carbon triple bond; therefore, it will use the primary suffixes “en” and “yne.”

Step 5: Identify any side chains or lower priority functional groups.

There are 2 other substituents attached to the parent chain: a propyl group and a bromine atom. Therefore, 2 prefixes are needed: “bromo-” and “propyl-” (listed in alphabetical order).

Step 6: Number the parent chain.

Shown above is the numbering of the parent chain. This direction was chosen in order to give the principal characteristic group the lowest possible number.

You can also now determine the locants. Both hydroxyl groups attach to the first carbon, the propyl group attaches to the third carbon, and the bromine atom attaches to the sixth carbon. In addition, the carbon-carbon double bond begins at the second carbon, and the carbon-carbon triple bond begins at the fourth carbon.

Step 7: Assign stereochemistry.

The carbon-carbon double bond uses the stereodescriptor “E.” Since there are no chiral centers in this compound, R or S configuration will not be utilized.

Step 8: Assemble the IUPAC name.

The IUPAC name of this compound is (E)-6-bromo-3-propylhex-2-en-4-yne-1,1-diol.

Further Reading

• Structural Isomers
• Enantiomers vs. Diastereomers
• Sn1 vs. Sn2 Reactions
• Understanding E1 vs E2 Reactions