IUPAC Nomenclature of Organic Compounds

 

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Contents 

What is IUPAC nomenclature?
General steps for IUPAC nomenclature of organic compounds:

IUPAC Nomenclature of organic compounds containing carbon to carbon single bonds and substituents only : [A]
IUPAC Nomenclature of organic compounds containing multiple bonds(double/triple bond) too. [B]
IUPAC Nomenclature of organic compounds containing one functional group ( monofunctional compounds): [C]
IUPAC Nomenclature of organic compounds containing more than one functional groups ( polyfunctional compounds) : [D]

• CONCLUSION :
• References :

What is IUPAC nomenclature?

This is a method of naming the organic compounds as recommended by the international Union of Pure and Applied Chemistry (IUPAC).

Each part of the IUPAC name gives you some useful information about the compound.

Before starting the IUPAC rules, lets see an example of organic compound and it’s IUPAC name.

To understand the name you need to take the name to pieces. In the given example “5-methylhex-3-en-2-ol” there are 4 pieces- ‘methyl’, ‘hex’, ‘en’ and ‘ol’.

‘methyl’ tells that –CH3 is present as substituent.

‘hex’ tells that there are 6 carbon atoms on parent carbon chain.

‘en’ tells that there is at least one carbon to carbon double bond.

‘ol’ tells that there is –OH group(alcohol) as functional group.

Thus, general format for IUPAC name of all compounds is:

IUPAC name of all compounds contain word root and primary suffix but prefix and secondary suffix may not be present because all organic compounds must contain carbon chain and bond but substituent and functional group may not be present. For example.

Now see the four parts ( prefix, word root, bond and functional group) separately.

 1. Word root : It indicates the parent carbon chain, which is the the longest continuous chain of carbon atoms including functional group and multiple bonds( if present).

No. of Carbon atoms in the parent chain	Word root
1	Meth-
2	Eth-
3	Prop-
4	But-
5	Pent-
6	Hex-
7	Hept-
8	Oct-
9	Non-
10	Dec-
11	Undec-
12	Dodec-

 2. Primary suffix : It indicates the nature of carbon to carbon bond in the parent carbon chain.

Nature of carbon to carbon bond	Primary suffix
Single	-ane
Double	-ene
Triple	-yne

 3. Secondary suffix : It indicates the parent(main) functional group present in the compound.

S. N.	Class or family	General structural   formula	Functional group	Secondary suffix
1	Carboxylic acid	Or RCOOH	Or -COOH	-oic acid
2	Sulphonic acid (sulfonic acid)	R-SO3H	-SO3H	-sulphonic acid
3	Acid anhydride			-oic anhydride
4	Ester	Or RCOOR	– COOR	-oate
5	Acid chloride	Or RCOCl	-COCl	-oyl chloride
6	Acid amide	Or RCONH2	Or -CONH2	-amide
7	Nitrile	Or RCN	-CN	-nitrile
8	Aldehyde	Or RCHO	Or -CHO	-al
9	Ketone			-one
10	Alcohol	R-OH	-OH	-ol
11	Thioalcohol	R-SH	-SH	-thiol
12	Amine	R – NH2	-NH2	-amine

 4. Prefix : It indicates the substituent ( i.e any group bonded with parent carbon chain except main functional group).

Substituent	Prefix
-CH3	Methyl-
-CH2CH3 or–C2H5	Ethyl-
-OCH3	Methoxy-
-OCH2CH3 or–OC2H5	Ethoxy-
-F	Fluoro-
-Cl	Chloro-
-Br	Bromo-
-I	Iodo-
-NO2	Nitro-
-NO	Nitroso-
-NH2	Amino-

{Note: -NH2 can be taken as substituent as well as functional group}

Sometimes, in case of compounds having polyfunctional groups, functional groups may be considered as prefixes. For example:

-OH	Hydroxy-
-CN	Cyano-
-CO-	Keto- (Carbonyl or Oxo-)
-CHO	Aldo- (Carbonyl or Oxo-)

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General steps for IUPAC nomenclature of organic compounds:

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Naming of all organic compounds can be done in three steps as,

To simplify the nomenclature process, differentiate the organic compounds in four categories as,

[A] Compounds containing carbon to carbon single bonds and substituents only.

[B] Compounds containing multiple bonds ( double/ triple bonds) too.

[C] Compounds containing one functional group ( monofunctional compounds).

[D] Compounds containing more than one functional groups ( polyfunctional compounds).

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IUPAC Nomenclature of organic compounds containing carbon to carbon single bonds and substituents only : [A]

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There are only three steps in nomenclature of all organic compounds.

Step-I : Selection of parent chain : The longest continuous carbon chain is selected as the parent chain. Eg.

If two or more equally long chains are present, the chain with maximum number of substituent is selected as the parent chain.

Step-II : Numbering the parent chain :

Lowest locant rule: Carbon bearing the substituent gets the lowest possible locant. Locant is a number that locate the position of substituent.

Note : Here the first locant is same (i.e 2) so compare second locant which is 2 and 4 in (2,2,4) and (2,4,4). Hence (2,2,4) is lowest set of numbering and is correct numbering.

If substituents are present at equivalent position, follow alphabetical order.

Step III – Naming : Alphabetically i.e. if more than one substituents are present then they are written in the alphabetical order.

 

 

Note: Naming of compounds containing complex substituent (alkyl group) : 

An alkyl substituent having substituents within itself is named in bracket by putting number outside. Eg.

 

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IUPAC Nomenclature of organic compounds containing multiple bonds(double/triple bond) too. [B]

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Step-I : Selection of parent chain : The longest continuous carbon chain including multiple bond is selected as the parent chain. Eg.

 

Step-II : Numbering the parent chain :

Lowest locant rule: Carbon bearing the multiple bond gets the lowest possible locant.

If both substituent and multiple bond are present, the priority order is:

Multiple bond > Substituent

If multiple bonds are present at equivalent position, follow alphabetical order i.e double bond(-ene) gets higher priority than triple bond(-yne).

Step III – Naming : Alphabetically i.e. if more than one substituents and multiple bonds are present then they are written in the alphabetical order.

 

 

Note: If both double and triple bonds are present, the terminal ‘e’ of first one(in name) is dropped(removed).

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IUPAC Nomenclature of organic compounds containing one functional group ( monofunctional compounds): [C]

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Step-I : Selection of parent chain : The longest continuous carbon chain including functional group is selected as the parent chain. Eg.

Step-II : Numbering the parent chain : Now the final priority order for numbering is :

Functional group > Multiple bond > substituent

 

Step III – Naming : Always follow this format:

For example,

 

NOTE : While adding the secondary suffix to the primary suffix, the terminal ‘e’ of the primary suffix (i.e., ane, ene or yne) is dropped if the secondary suffix begins with a vowel. However, the terminal ‘e’ is retained if the complete secondary suffix begins with a consonant.

Some examples of IUPAC names for compounds containing one functional group:

Class or family	General formula	Examples
Carboxylic acid	Or RCOOH
Sulphonic acid (sulfonic acid)	R-SO3H
Ester	Or RCOOR
Acid chloride	Or RCOCl
Acid amide	Or RCONH2
Nitrile	Or RCN
Aldehyde	Or RCHO
Ketone
Alcohol	R-OH
Amine	R – NH2

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IUPAC Nomenclature of organic compounds containing more than one functional groups ( polyfunctional compounds) : [D]

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The priority order of functional groups is:

-COOH > -SO3H > – COO- > -COX > -CONH2 > -CN > -CHO > -CO- > -OH > -NH2

During nomenclature of polyfunctional compounds, fuctional group of higher priority is taken as principal functional group and other functional groups are considered as substituents.

The IUPAC rules applied for monofunctional compounds are also applied for polyfunctional compounds. Some additional rules are needed, which are given below:

At first, principal functional group is identified according to priority order. Eg.

Step-I : Selection of parent chain : The longest continuous carbon chain with principal functional group is selected as the parent chain. Eg.

Step-II : Numbering the parent chain : Principal functional group gets lowest locant(number).

Step III – Naming : Substituents are written in alphabetical order as mentioned earlier. Eg.

Some other examples of polyfunctional compounds :

 

 

• If a compound contains two or more functional groups, the words –di, -tri, -tetra, etc. is written before the name of secondary suffix with respective locant numbers. In such cases, the last letter ‘e’ from primary suffix is not dropped (removed). Eg.

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CONCLUSION :

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Nomenclature of organic compounds is very easy. Remember only two things (mentioned below) during nomenclature, you will easily write correct IUPAC name of all organic compounds.

1. Always follow three steps :

2. Always write the name in general format :

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References :

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• Bahl, B.S., A., Advanced Organic Chemistry, S. Chand and company Ltd, New Delhi, 1992.
• Finar, I. L., Organic Chemistry, Vol. I and Vol. II, Prentice Hall, London, 1995.
• Ghosh, S.K., Advanced General Organic Chemistry, Second Edition, New Central Book Agency Pvt. Ltd., Kolkatta, 2007.
• https://iupac.org/what-we-do/nomenclature/
• https://app.biorender.com/illustrations/edit/5ed85ef66c525700aadc31bf
• https://en.wikipedia.org/wiki/Preferred_IUPAC_name