Nomenclature of Organic Compounds: Rules, Examples

Nomenclature means the system of naming organic compounds based on specific guidelines. A set of logical rules was devised and used by organic chemists to circumvent problems caused by arbitrary nomenclature. Nomenclature of organic compounds is defined as the systematic approach taken for the nomenclature of the organic compounds as per the recommendation of IUPAC.

The name of an organic compound involves three parts namely, a word root, suffix, and prefix. In this article, we will discuss about the nomenclature of organic compounds in detail. Scroll down to learn more!

What is the Nomenclature of Organic Compounds?

Nomenclature means the system of naming organic compounds based on specific guidelines. This is also quite necessary; otherwise, it will be very difficult to assign names to the vast number of organic compounds and remember them. There are two systems of Nomenclature, namely:

1. Trivial or Common System 
2. IUPAC system

1. Trivial or Common System

A non-systematic name for a chemical compound is known as a trivial name in chemistry. That is, according to the rules of any formal system of chemical nomenclatures, such as IUPAC inorganic or IUPAC organic nomenclature, the term is not accepted.

2. IUPAC Nomenclature of Organic Compounds

Organic chemistry deals with a huge number of different molecules. A systematic way of naming has been devised to clearly identify them, and it is known as the IUPAC (International Union of Pure and Applied Chemistry).

General Rules for IUPAC Nomenclature

According to the IUPAC system, the name of an organic compound, in general, consists of the following three parts:

1. Word root
2. Suffix
3. Prefix

(i) Word Root

Word root denotes the number of carbon atoms present in the principal chain, which is the longest possible chain of carbon atoms. For chains from one to four carbon atoms, special word roots (based upon the common names of alkanes) are used, but for chains of five or more carbon atoms, Greek number roots are used as given below:

Note: Extra ‘a’ given in parenthesis is used only if the primary suffix to be added to the word root starts with a constant.

(ii) Suffix

The main functional group and the multiple bonds present in the given compounds are indicated by adding specific suffixes to the word root. The suffixes used are of two types as given below;

1. Primary suffix: The suffix used to represent the saturation or unsaturation of carbon atoms present in the parent chain is called a primary suffix. The basic primary suffix is given below:

If the carbon chain contains more than one double or triple bond, their number is indicated by numerical prefixes such as di, tri, or tetra.

For example;

b. Secondary suffix: The suffix used to represent the nature of the principal functional group present in the compound is called a secondary suffix.  

For example, 

It may be noted that while adding a secondary suffix to the primary suffix, the terminal ‘\({\rm{e}}\)’ of the primary suffix is dropper if the secondary suffix begins with ‘\({\rm{a}}\)’, ‘\({\rm{i}}\)’, ‘\({\rm{o}}\)’, ‘\({\rm{u}}\)’ or ‘\({\rm{y}}\)’.

For example;

(iii) Prefix

Prefix is a part of the IUPAC name which appears before the word root. Prefixes are of two types.

a. Primary prefix: A primary prefix cyclo is used in order to differentiate a cyclic compound from an acyclic compound.

For example;

b. Secondary prefix: In the IUPAC system of Nomenclature, certain characteristic groups are not considered functional groups or secondary suffixes. These are regarded as substituents and are denoted by secondary prefixes. Some secondary prefixes are given below: 

Nomenclature of Organic Compounds Table

The nomenclature of organic compounds is tabulated below:

Primary Suffix of Organic Compounds

Name of the Compound Containing Word Root, Primary Suffix and Secondary Suffix

Functional Groups

The functional groups are as follows:

Class of Organic Compounds	Functional group	Secondary Suffix
Alcohol	\(- {\rm{OH}}\)	-ol
Thioacohol	\(- {\rm{SH}}\)	-thiol
Aldehyde	\(- {\rm{CHO}}\)	-al
Ketone		-one
Carboxylic acid	\(- {\rm{COOH}}\)	-oic acid
Acid chloride	\(- {\rm{COCl}}\)	-oyl chloride
Amide	\({\rm{ – CON}}{{\rm{H}}_{\rm{2}}}\)	-amide
Ester	\(- {\rm{COOR}}\)	-oate
Nitrile	\(- {\rm{CN}}\)	-nitrile
Amine	\(- {\rm{ N}}{{\rm{H}}_2}\)	-amine

Substituents Groups

The substituents groups are as follows:

Nomenclature of Organic Compounds Examples

We know that the IUPAC name of a compound consists of word root, primary and secondary suffixes. While writing the complete IUPAC name of a compound following points are necessary to be followed;

The sum up IUPAC name of an organic compound consists of the following arrangement.

\({\rm{Prefix (es) + Word root + Primary suffix + Secondary suffix}}\)

Some of the examples are given below:

1. \(C{H_4}\)

This compound contains one carbon atom hence word root is Meth- and it contains single bond, so the primary suffix is -ane.

Thus, the IUPAC name of this compound is Methane. 

2.

Word root: Prop

Prefix: methyl (is at the second position)

Primary suffix: -ane

Secondary suffix: -ol (at first position)

Thus, the complete IUPAC name of the compound can be written as

\({\rm{2 –  –  –  –  – }}\mathop {{\rm{methyl}}}\limits_{\left( {{\rm{Prefix}}} \right)} {\rm{ –  –  –  –  –  –  – }}\mathop {{\rm{prop}}}\limits_{\left( {{\rm{Word}}\,{\rm{root}}} \right)} {\rm{ –  –  –  –  – }}\mathop {{\rm{ane}}}\limits_{\left( {{\rm{P}}{\rm{.}}\,{\rm{suffix}}} \right)} {\rm{ –  –  –  –  – }}\mathop {\rm{1}}\limits_{\left( {{\rm{S}}{\rm{.}}\,{\rm{suffix}}} \right)} {\rm{ –  –  –  –  – ol}}\)

Hence, the IUPAC name of given compound is \(2\)-methylpropan\(-1\)-ol

Ans: The compound is substituted octane; It has branches at carbon -\(3\), carbon-\(4\) and carbon-\(5\). Thus, the name is \(4\)-sec-butyl-\(5\)-ethyl-\(3\)-methyloctane.

Nomenclature of Organic Compounds with Functional Groups

The chemical behaviour of an organic compound is governed by the functional group present in it. The presence of a functional group is indicated by adding a particular suffix to the name of the corresponding hydrocarbon.

A functional group is an atom or group of atoms bonded together in a unique manner, usually the site of chemical reactivity in an organic molecule.

For example, the suffix for a functional group \({\rm{ – OH}}\) is –ol. Therefore, the compound \({\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{OH}}\) would be named as methanol because its parent hydrocarbon is methane.

Some important functional groups and corresponding suffixes and prefixes are given in the table.

S. No.	Class of Compound	Functional Group	IUPAC Suffixes(s) or Prefixes	General IUPAC Name	Example
1	Alcohol	\(- {\rm{OH}}\)	-ol(s)	Alkanol	Ethanol
2	Ether	\(- {\rm{OR}}\)	Alkoxy – (p)	Alkoxy alkane
3	Aldehyde		-al (s)	Alkanal
4	Ketone		-one (s)	Alkanone
5	Carboxylic acid		-oic acid (s)	Alkanoic acid	Ethanoic acid
6	Acyl halide		-oyl halide (s)	Alkanoyl halide
7	Amide		-amide (s)	Alkanamide
8	Acid anhydride		-oic anhydride (s)	Alkanoic anhydride	Ethanoic anhydride
9	Ester		-yl (s) for R’And –oate (s) for R –COO part	Alkyl alkanoate	Propyl ethanoate
10	Halide	\({\rm{ – X }}\left( {{\rm{X = F, Cl, Br, I}}} \right)\)	Halo – (p)	Halo alkane
11	Nitro		Nitro – (p)	Nitro alkane
12	Amine	\({\rm{ – N}}{{\rm{H}}_{\rm{2}}}\)	-amine (s)	Alkanamine
13	Cyanide	\({\rm{ – CN}}\)	-nitrile (s)	Alkane nitrile
14	Thiolcohol	\({\rm{ – SH}}\)	-thiol (s)	Alkane thiol

Compounds Containing Only One Functional Group

The longest chain of carbon atoms containing the functional group is numbered so that the functional group is attached to the carbon atom possessing the lowest possible number in the chain.

For example,

The functional group present is -OH. The corresponding secondary suffix is \({\rm{ – ol}}.\) Since the addition of primary suffix ane to word root pent gives pentane, adding a suffix \({\rm{ – ol}}\) to pentane gives pentanol. The functional group is present at the second carbon atom of the chain. Therefore, the IUPAC name of the compound is pentan \(- 2 – {\rm{ol}}{\rm{.}}\).

Practice Questions on Nomenclature of Organic Compounds

Q.1. Give the IUPAC name of the compound \({\rm{C}}{{\rm{H}}{\rm{3}}}{\rm{C}}{{\rm{H}}{\rm{2}}}{\rm{C}}{{\rm{H}}{\rm{2}}}{\rm{C}}{{\rm{H}}{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{3}}}\)
Ans: This compound contains five carbon atoms hence word root is Pent- and it contains single bonds so the primary suffix is -ane. Thus, the IUPAC name of this compound is Pentane. 

Q.2. Give the IUPAC name of the compound:

Ans: Word root: Pent
Prefix: methyl (is at the second position)
Primary suffix: -ane
Thus, the IUPAC name is \(3\)-methylpentane.

Q.3. Give the IUPAC name of the compound:

Ans: The compound is substituted octane; It has branches at carbon-\(3\), carbon-\(4\) and carbon-\(5\). Thus, the name is \(4\)-sec-butyl-\(5\)-ethyl-\(3\)-methyloctane.

Q.4. Give the IUPA name of the compound

Ans: The given compound can be written as  \(4\)-chloro-ethyl \(-3, 5, 7\)-trimethyl \(-6\) -nitronoan-\(1\)-one

Summary

Nomenclature means the system of naming organic compounds based on certain guidelines. A systematic method of naming them has been developed in order to identify them. According to the IUPAC system, the name of an organic compound, in general, consists of three parts: Word root, primary suffix, and prefix. The suffix used to represent the saturation or unsaturation of carbon atoms present in the parent chain is called a primary suffix.

Attempt Mock Tests

FAQs on Nomenclature of Organic Compounds

Q.1. How do you write an organic compound nomenclature?
Ans: 
1. Find the longest continuous chain of carbon atoms and use its name as the base name for the compound.
2. Beginning with the end of the chain closest to a substituent, number the longest chain.
3. If a substituent appears more than once, the prefix di, tri, or tetra is used with the location of the carbon on which it appears.
4. Write the alkyl groups in alphabetical order regardless of their position on the chain.
5. Cyclic hydrocarbon has the prefix cyclo before the name.

Q.2. What are the rules for naming organic compounds?
Ans:  Following are the rules for writing naming organic compounds
Rule 1: Find the longest continuous chain of carbon atoms and use its name as the base name for the compound.
Rule 2: Beginning with the end of the chain closest to a substituent, number the longest chain.
Rule 3: If a substituent appears more than once, the prefix di, tri, or tetra is used with the location of the carbon on which it appears.
Rule 4: Write the alkyl groups in alphabetical order regardless of their position on the chain.
Rule 5: Cyclic hydrocarbon has the prefix cyclo before the name.

Q.3. What is the classification, nomenclature, and isomerism of organic compounds?
Ans: Organic compounds are classified into aliphatic compounds, saturated and unsaturated compounds, aromatic compounds, alicyclic compounds and heterocyclic compounds.
Nomenclature means the system of naming organic compounds based on certain guidelines.
Isomerism is a phenomenon in organic chemistry that occurs when two or more organic compounds with the same chemical formula have distinct properties due to differences in atom arrangement along with the carbon skeleton or in space. 

Q.4. Why is IUPAC nomenclature needed?
Ans: The goal of the IUPAC nomenclature system is to create an international standard for naming compounds in order to facilitate communication.

Q.5. How to learn the nomenclature of organic compounds?
Ans:
1. The arrangement of the different parts of the name is as follows:
Prefix(es) + Word root + Primary suffix + Secondary suffix
2. The position of each substituent is represented by putting a suitable number before the corresponding prefix. Prefixes are arranged in alphabetical order and are separated by hyphens (-).
3. If the primary suffix is –ane, the position of the primary functional group is indicated by mentioning the appropriate number before the secondary suffix, separated by hyphens on both sides.
4. If the primary suffix is –ene or –yne, the number indicating the position of the double or triple bond is written before the primary suffix separated by hyphens, and the number indicating the position of the principal functional group is written before the secondary suffix separated by hyphens.
5. The prefix cyclo is written right before the word root in the case of cyclic compounds.

Q.6. What does nomenclature mean in chemistry?
Ans: A chemical nomenclature is a set of rules for naming chemical substances in a systematic way.

Q.7. How do you write the common name of organic compounds?
Ans:

Q.8. What is compound and give \(5\) examples?
Ans: A compound is a material made up of two or more chemical elements that have been chemically bonded together.
Examples of compounds are water, salt, glucose, baking soda, acetic acid.

Q.9. Why is nomenclature important?
Ans:  The basic goal of chemical nomenclature is to ensure that a chemical name, whether spoken or written, is clear about which chemical compound it refers to: Each chemical name should be associated with a specific substance.

Learn About Nomenclature Here

We hope this article on the Nomenclature of Organic Compounds has helped you. If you have any queries, drop a comment below and we will get back to you