IUPAC Nomenclature of Functional Group, Polyfunctional Compounds, Compounds With More than Two Principal Functional Groups, Practice Problems & FAQ

We have seen so many different colours around us in our daily lives, and there is some specific name for each different colour by which we can easily distinguish different colours. In the same way, the IUPAC nomenclature is used to classify, investigate, and analyze a large number of organic compounds. It allows us to give each chemical compound a unique identification.

Table of content

Functional Groups Priority Order Table
Rules to assign IUPAC naming to Functional Groups
Assigning Locants
IUPAC Nomenclature of Cyclic Compounds having Functional Groups
IUPAC Nomenclature of Polyfunctional Compounds
IUPAC Nomenclature of Compounds with more than two Principal Functional Group
Practice Problems
Frequently asked questions

Functional Groups Priority Order Table

Functional groups are given in decreasing order of their priority in the following table. They are to be considered while numbering.

Class	Name	Prefix	Suffix
R-COOH	Carboxylic acid	carboxy	-oic acid
R-SO₃H	Sulphonic acid	sulpho	-sulphonic acid
(R-CO)₂O	Acid anhydride	-	-anhydride
R-COOR	Ester	carboalkoxy	-oate
R-COX	Acid halides	halo carbonyl	-oyl halide
R-CONH₂	Amides	carbamoyl/carboxamide	-amide
R-CN	Cyanide	cyano	-nitrile
R-CHO	Aldehyde	formyl/oxo	-al
R-COR	Ketone	keto/oxo	-one
R-OH	Alcohol	hydroxy	-ol
R-SH	Thiol	mercapto	-thiol
R-NH₂	Amines	amino	-amines
R-OR	Alkoxy	-	-
-O-	Epoxy	-	-

Rules to assign IUPAC naming to Functional Groups

Basic skeleton of IUPAC naming system :

Secondary prefix + Primary prefix + Word root + Primary suffix + Secondary suffix

Secondary prefix - denotes the substituents attached to the parent chain

Primary prefix - denotes the nature of the parent chain (cyclo, bicyclo, spiro)

Root Word - denotes the number of carbon atoms in the parent chain

Primary Suffix - denotes the saturation/unsaturation of the parent chain

Secondary Suffix - denotes the principle functional group

Given rules need to be followed for assigning names to functional groups containing compounds.

Select the longest possible carbon chain which contains the highest priority functional group.
If the number of functional groups is the same, then select the carbon chain that contains the maximum number of multiple bonds.
If the number of functional groups and multiple bonds is the same, then select the carbon chain which contains more number of substituents.
If the number of substituents is also the same, then choose the carbon chain that has an early point of difference. If the point of difference is also the same, then choose the carbon chain according to the alphabetical order of the substituents.

The order of selection of parent chain is given as follows:

Assigning Locants

The main functional group should get the lowest numbering while assigning the locants.
If the same functional group is repeated, then the numbering should be done in such a way that both the functional groups should get the lowest numbering while assigning the locants.
If the functional group gets the same numbering, then the numbering should start in such a way that the multiple bonds should get the lowest numbering.
If the multiple bonds get the same number, then the numbering should start in such a way that the maximum number of substituents gets the lowest number. If the substituents also get the same number, then the numbering should follow the alphabetical order of the substituents.

The order of selection of parent chain is given as follows:

Note:

A functional group which is always numbered as 1 are –COOH, –COOR, –COX, –CONH₂, –CN, or –CHO.
If a compound contains two or more like (similar) groups, then the numerical prefixes di, tri, tetra, etc., are used.

Example:

IUPAC Nomenclature: Pentane-2,4-dione

	Example 1	Example 2
Compound Structure
IUPAC Nomenclature	2-Methylbutanoic acid	Pent-3-ynal

Example:

Determine the parent chain and IUPAC nomenclature of the given compound.

Answer:

Selection of Parent Chain:- In this case, the alcohol group is the highest priority functional group. In this compound, there are two −OH groups. Therefore, to locate the parent chain, both the alcohol groups should take part in the parent chain.

Position of substituents:- In the parent chain, there are five carbon atoms. Two alcohol functional groups are attached at the first and fifth positions. The double bond and the alkenyl substituent are in the second and fourth positions, respectively.

IUPAC Nomenclature:- 4-(1-Chloroethenyl)pent-2-ene-1,5-diol

IUPAC Nomenclature of Cyclic Compounds having Functional Groups

When functional groups containing carbon are directly connected to a ring, the ring is considered the parent chain. A special suffix is used for these functional groups that are given as follows:

Functional Group	Special Suffix	Example	IUPAC Nomenclature
-CHO	Carbaldehyde		Cyclopentanecarbaldehyde
-COOH	Carboxylic acid		Cyclohexanecarboxylic acid
-COX	Carbonyl halide		Cycloheptanecarbonyl chloride
-COOR	carboxylate		Cyclohexyl cyclohexanecarboxylate
-CONH₂	Carboxamide		Cyclopropanecarboxamide
-CN	Carbonitrile		Cyclopentanecarbonitrile

IUPAC Nomenclature of Polyfunctional Compounds

When an organic compound contains two or more than two different functional groups, then select the principal functional group according to the priority list and another functional group left will be treated as a substituent and prefix will be used.

Examples:

Compound Structure	Explanation	IUPAC Nomenclature
	Parent chain contains four carbon atoms.A Carboxylic acid functional group is the highest priority group. Therefore, the suffix and prefix are used for the carboxylic acid group and alcohol group, respectively.	3-Ethyl-2-hydroxybut-3- enoic acid
	Parent chain contains five carbon atoms. The acid chloride group is the highest priority group, the suffix and prefix are used for the acid chloride group and amine group, respectively.	4-Aminopentanoyl chloride
	Parent chain contains nine carbon atoms. Carboxylic acid group is the highest priority group, -oic acid is used as a suffix, and the prefix used is formyl for the aldehyde group.	6-Formylnonanoic acid
	Parent chain contains four carbon atoms. Carboxylic acid group is the highest priority group, -oic acid is used as a suffix and prefix used is carboxamide for amide group	4-Carboxamidebutanoic acid
	In the parent chain, there are six carbon atoms. Since the aldehyde group is given the highest priority, -al is used as a suffix, and the prefix used is 1-hydroxyethyl for alkyl containing -OH group	4-(1-hydroxyethyl)hex-5- enal

IUPAC Nomenclature of Compounds with more than two Principal Functional Group

When more than two carbon-containing functional groups except ketone (chain-terminating functional groups) are attached directly to an open chain, the carbon of the functional group of all the functional groups are excluded from the parent chain. A special and common suffix is used for the functional group.

Chain-terminating groups: These are the functional groups that are used at the end of the chain.

Examples: −COOH, −CHO,−CN

Examples:

Compound Structure	IUPAC Nomenclature
	Heptane-1,3,4,7-tetracarboxylic acid
	Propane-1,2,3-tricarbaldehyde

Practice Problems

Q. 1. Write the IUPAC name of the given compound.

Solution:

Since the functional group −OH is given priority over alkyl branches, the 1st position will be given to the carbon connected to the −OH group. Therefore, the IUPAC name of the compound is 3,3-dimethyl-1-cyclohexanol.

Q. 2. Write the IUPAC name of the compound.

Solution:

Since the functional group −COOH is given priority over -OH, the 1st position will be given to the carbon connected to −COOH group. Therefore, the IUPAC name of the compound is 3-Ethenyl-3-hydroxy-4-methylhex-5-ynoic acid.

Q. 3. Write the IUPAC name of the compound.

Solution:

In the given compound, the functional group is an ester with a 2-chloropropyl group attached to the O‒atom. So, the IUPAC name of the compound is 2-chloropropyl-3-bromobut-2-enoate.

Q. 4. Write the IUPAC name of the compound.

Solution:

Here, the functional group is an ester with cyclopenta-2,4-dienyl attached to the oxygen atom and two double bonds at the 2nd and 4th carbons of the parent chain. So, the IUPAC name of the compound is

cyclopenta-2,4-dienylpenta-2,4-dienoate.

Q. 5. Write the IUPAC name of the compound.

Solution:

In this compound, there are two symmetrical ester groups in its molecule with methyl groups bonded to the O ‒ atom. So, the IUPAC name of the compound is dimethylpentane-1,5-dioate.

Frequently asked questions

Q. 1. When is a special suffix used in IUPAC nomenclature?
Answer: When functional groups containing carbon are directly connected to a ring and more than three identical functional groups are connected to a single carbon chain, a special suffix is used in these cases.

Q. 2. When is formyl used as a prefix for aldehyde?
Answer: When the Carbon atom of aldehyde is not a part of the parent chain then formyl is used as a prefix.

Q. 3. Which functional group has more priority Sulphonic acid or Acid anhydride?
Answer: When a molecule contains more than one functional group, then one will be used as a principal functional group and the other functional group will be used as a substituent. Among sulphonic acid or acid anhydride, more priority is given to sulphonic acid than to acid anhydride.

Related Topics

Nomenclature of functional groups	Classification of organic compounds
Nomenclature of Saturated Hydrocarbons	IUPAC nomenclature of unsaturated hydrocarbons