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What Is Nomenclature: Nomenclature, IUPAC Rules and Examples of Nomenclature Organic Compounds, Practice Problems & Frequently Asked Questions

What Is Nomenclature: Nomenclature, IUPAC Rules and Examples of Nomenclature Organic Compounds, Practice Problems & Frequently Asked Questions

Imagine a biopic or a biography of a famous personality. How do you identify or spot that person? Your probable answer would be, by his official name, which we also call "good name". This person could be a famous actor, who has portrayed multiple famous roles or characters in his lifetime. He would have become synonymous with so many of his famous roles and would be famous in those names pertaining to all those famous characters. But if we are to spot him in reality, and address him officially, we would have to use his "good name".

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Chemical compounds are several million in number, and many of them have multiple names classified as common names, trivial names, commercial names, formula names etc. So, systematic naming rules are required to create a name that will be accepted universally for old as well as newly discovered compounds also. This is the scope of the members of the committee of the International Union of Pure and Applied Chemistry (IUPAC). The rules to be followed in naming a chemical compound under it are called IUPAC nomenclature.

Let us learn the important rules relevant to us and try to nomenclature some organic compounds ourselves.

Table of Contents:

  • Nomenclature of Organic Compounds
  • IUPAC Rules For Naming Compounds
  • Examples of Nomenclature of Organic Compounds
  • Practice Problems
  • Frequently Asked Questions(FAQs)

Nomenclature of Organic Compounds:

The system of naming chemical compounds based on predetermined rules is known as nomenclature. Otherwise, it will be quite impossible to provide names to the enormous variety of organic compounds and remember them, thus this is also quite necessary. There are two nomenclature systems, namely:

1. Trivial name or common name

2. IUPAC name

1. Trivial name or common name:

In earlier times, compounds are named based on several nonuniform reasons. When an organic compound was first discovered, chemists would often give it a historical name based on how it had been made. For instance, the wood spirit was given this name because it was made by the destructive distillation of wood. Methyl alcohol is the modern name for this combination (methu is the Greek word for wine and hule is the word for wood). Like vinegar, of which it is the main component, acetic acid gets its name from the Latin word acetum. These names are referred to as trivial names or common names.

The following table shows the common name, source and structure of the organic compounds

S.No

Common Name

Source

Structure

1.

Formic acid

Formica(red ant)

HCOOH

2.

Acetic acid

Acetum(vinegar)

CH3COOH

3.

Propionic acid

Portpion(first fat)

CH3CH2COOH

4.

Butyric acid

Butyrum(butter)

CH3CH2CH2COOH

5.

Valeric acid

valerian(shrub)

CH3CH2CH2CH2COOH

6.

Caproic acid

Caper(goat)

CH3CH2CH2CH2CH2COOH

7.

Urea

Urine

NH2CONH2

8.

Malic acid

Malum(apple)

HOOCCH2-CH(OH)COOH

9.

Methyl alcohol

Methu hule

(methu=wine hule=wood)

CH3OH

2. IUPAC names: The International Union of Pure and Applied Chemistry (IUPAC) recommends the systematic naming of organic compounds using the IUPAC nomenclature. Nomenclature is on the assumption that compounds are obtained by the substitution of hydrogen by an active group called a functional group in a hydrocarbon. Based on the principal functional group and principle hydrocarbon chain, this method uses substitutive nomenclature.

IUPAC Rules For Naming Compounds:

An organic compound's name is composed of three elements according to IUPAC:

(i) Word root

(ii) Prefix

(iii) Suffix

Word Root: This indicates the core hydrocarbon, which has undergone substitutions. It corresponds to the principle carbon chain, having the longest skeleton of the carbon chain that is possible.

Chain length

Word root

Chain length

Word root

C1

Meth

C7

Hept

C2

Eth

C8

Oct

C3

Prop

C9

Non

C4

But

C10

Dec

C5

Pent

C11

Undec

C6

Hex

C12

Dodec

Prefix: These are written before the word root. There are two types of prefixes namely

(i) Primary prefix:

Specifies the nature of the parent chain, as whether it is cyclic, bicyclic or spiral. If present they are indicated by a prefix of cyclo, bicyclo or spiro respectively.o distinguish between cyclic and acyclic compounds, the primary prefix cyclic is used.

For example:

CH3CH2CH3

Propane

Cyclopropane

CH3CH2CH2CH2CH3

Pentane

Cyclopentane

(ii) Secondary Prefix:

This indicates the nature of substituents, Among the substituents, some are always represented as secondary prefixes. When multiple substituents are present, an order of priority is given to them. Except that of the most prioritised functional group, all others are considered substituents and included in the nomenclature as secondary prefixes.

The substituents that are always in the secondary prefix are given below

Substituents

Secondary Prefix

Substituents

Secondary

Prefix

-F

Fluoro

-N=N-

Diazo

-Cl

Chloro

-OR

Alkoxy

-Br

Bromo

-OCH2CH3

Ethoxy

-I

Iodo

-OH

Hydroxy

-NO2

Nitro

-R

Alkyl

-NO

Nitroso

-C2H5

Ethyl

Suffix:

Suffix to the word root gives information on the saturation and the primary functional group of the organic compound. The suffixes are also of two categories:

(i) Primary suffix:

The primary suffix describes the level of unsaturation of the parent hydrocarbon of the given compound.

If only single bonds are present in the parent chain, the compound is fully saturated with the primary suffix ‘ane’.

If single and double bonds only are present in the parent chain, the compound is unsaturated and has the suffix ‘ene’.

If single and triple bonds only are present in the parent chain, then the primary suffix ‘yne’ is used.

If there is more than one double or triple bond present in the carbon atom, its number is denoted by a numerical prefix like di, tri, or tetra.

If a carbon chain contains two double bonds then the primary suffix ‘diene’ is used.

If the carbon chain contains three double bonds then the primary suffix ‘triene’ is used.

If the carbon chain contains three triple bonds then the primary suffix ‘triyne’ is used.

If both double and triple bonds are present, the prefix will be ‘eneyene’.

(ii) Secondary suffix:

The term "secondary suffix" refers to the nature of the functional group that is present in the compound.

The functional groups in the table below are listed in decreasing priority order. When more than one of them is present, the most priority substituent will be the functional group to become a suffix.

Substituent

Name of the functional group

Secondary Prefix

Secondary 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

Examples of Nomenclature of Organic Compounds:

The IUPAC name system's basic structure:

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

Secondary prefix - corresponds to the substituents attached to the parent chain

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

Root Word - corresponds to the number of carbon atoms in the parent chain

Primary Suffix - corresponds to the saturation/unsaturation of the parent chain

Secondary Suffix - corresponds to the principal functional group.

Example-1: CH3CH2CH2CH3

The given compound is an alkane.

Word root: The parent chain is of four carbon atoms. So, ‘but’ will be the word root.

Primary suffix: Fully saturated hydrocarbon. So ‘ane’.

Hence, the compound's IUPAC name is Butane.

Example 2:

The given compound is a carboxylic acid.

Word root: The parent chain consists of five carbon atoms. So, ‘pent’ will be the word root.

Secondary Prefix: The numbering has to start from the carboxylic acid functional group and at the second and third carbons of the molecule each has one methyl substituent. Therefore, the 2,3-dimethyl prefix will be used.

Primary Suffix: The molecule has a carbon-carbon double bond in the second position, hence the primary suffix will be 2-ene.

Secondary Suffix: The compound has the functional group carboxylic acid, hence the secondary suffix will be -oic acid.

Therefore, the compound IUPAC name is 2,3-dimethylpent-2-enoic acid.

Example 3:

The given compound is a carboxylic acid.

Word root: The parent chain consists of four carbon atoms. So, but will be the word root.

Prefix: No substituents connected to the parent carbon chain.

Primary Suffix: The compound contains a carbon-carbon single covalent bond, so ‘ane’ will be used as a primary suffix.

Secondary Suffix: The compound contains two carboxylic acids as functional groups, so -’dioic acid’ will be used as a secondary suffix.

Therefore, the IUPAC name of the compound is Butan-1,4-dioic acid or 1,4-Butanedioic acid.

Example-4:

The given compound is a carboxylic acid.

Word root: The parent chain consists of six carbon atoms. So, ‘hex’ will be the word root.

Primary Prefix: It is a cyclic compound. So, ‘cyclo’ is used as a prefix

Primary Suffix: The compound contains Carbon-carbon single covalent bond only, so ‘ane’ will be used as a primary suffix.

Secondary Suffix: The compound contains carboxylic acids outside the hydrocarbon chain as functional groups, so carboxylic acid will be used as a secondary suffix.

Therefore, the IUPAC name of the compound is Cyclohexane Carboxylic acid.

Practice Problems:

Q1. What is the following compound IUPAC name?

Solution: If the terminal carbon has a double bond and any other carbon in the molecule has a triple bond. Numbering will then begin with a double bond as shown below

The compound consists of five carbon atoms so pent will be the word root and there are double and triple bonds. So the compound’s IUPAC name is Pent-1-ene-3-yne.

Q2. What is the following compound IUPAC name?

Solution: If there is an unsaturated bond, such as a double or triple bond, at the terminal carbon atom, the numbering always begins at the double-bonded carbon atom. (A double bond is preferred over a triple bond when both bonds are in the same place).

The compound consists of four carbon atoms. So, but will be the word root and there are double and triple bonds. So the compound’s IUPAC name is But-1-ene-3-yne.

Q3. What is the following compound IUPAC name?

Solution:

The given compound is carboxylic acid.

Word root: The parent chain consists of five carbon atoms. So, ‘pent’ will be the word root.

Prefix: At the 3rd position, there is nitro so the prefix is 3-nitro

Primary Suffix: The compound’s carbon chain contains two double bonds at the 2nd and the 4th position then the primary suffix 2,4-diene is used.

Secondary Suffix: The compound contains carboxylic acids as functional groups, so’ -oic’ acid will be used as a secondary suffix.

Therefore, the compound’s IUPAC name is 3-nitro pent-2,4-dienoic acid.

Q4. What is the following compound IUPAC name?

Solution:

The given compound contains carboxylic acid and ketone. Here the priority functional group is carboxylic acid so a secondary suffix is used and for ketone secondary prefix is used

Word root: The parent chain consists of five carbon atoms. So,’ pent’ will be the word root.

Secondary Prefix: 4-oxo

Primary Suffix: The compound’s carbon chain contains a carbon-carbon single bond only. So ‘ane’ is used as the primary prefix

Secondary Suffix: In the compound, the priority functional group is a carboxylic acid, so ‘-oic’ acid will be used as a secondary suffix.

Therefore, the compound’s IUPAC name is 4-oxo pentanoic acid or 4-oxo pentan-1-oic acid.

Frequently Asked Questions(FAQs):

Q1. What is the purpose of IUPAC nomenclature?
Answer:
The IUPAC system of nomenclature aims to create an international standard for identifying chemicals in order to improve communication. The system's aim is to associate each name with a distinct and clear structure while also giving each structure a unique and unambiguous name.

Q2. Mention the order of the selection of the parent chain.
Answer:
The parent chain selection order is given as follows:

Q3. Name the functional groups with two prefixes.
Answer:
Depending on the connection of the group, there will be two alternative prefixes used for a functional group in polyfunctional groups comprising compounds. Aldehydes employ formyl and oxo, ketone uses oxo and keto, while esters use alkoxy carbonyl and alkanoyl oxy.

Q4. The functional group present in the following compound is

Answer: The functional group present in the given molecule is an ester (R-COOR) and its secondary suffix is -oate.

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