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Home » Class 11 » Chemistry » Organic Chemistry - Some Basic Principles and Techniques » Nomenclature of Organic Compounds

Nomenclature of Organic Compounds

Last Updated on February 16, 2023 By Mrs Shilpi Nagpal

Nomenclature means the system of naming of organic compounds. In case of aliphatic compounds, two system of nomenclature generally used are:

(1) Trivial or common system

(2) IUPAC system

Contents

  • 1 Trivial or Common System
  • 2 IUPAC system
  • 3 General Rules for IUPAC Nomenclature of Organic Compounds
    • 3.1 Word root
    • 3.2 Suffix
      • 3.2.1 (1) Primary suffix
      • 3.2.2 (2) Secondary suffix
    • 3.3 Prefix
      • 3.3.1 (1) Primary Prefix
      • 3.3.2 (2) secondary prefix 

Trivial or Common System

Organic compounds were named after the source from which they were first isolated.

For example : Urea got its name since the compound was first obtained from the urine of mammals.

Methyl alcohol was called wood spirit since it could be obtained by the destructive distillation of wood.

Acetic Acid got its name from the acetum since it is present in vinegar.

Formic acid was derived from formicus since it could be obtained by the destructive distillation of red ants.

Citric acid is named so because it is found in citrus fruits.

Common or Trivial names of some organic compounds:

Compound Common Name
CH4 Methane
C2H2 Acetylene
CH3CH2CH2CH3 Butane
(CH3)2CHCH3 Isobutane
(CH3)4C Neopentane
CHCl3 Chloroform
CH3CH2OCH3 Ethyl Methyl ether
HCHO Formaldehyde
(CH3)2CO Acetone
CH3COOH Acetic acid
CH3CONH2 Acetamide
CH3CN Acetonitrile
C6H6 Benzene
C6H5OH Phenol
C6H5OCH3  Anisole
 C6H5NH2  Aniline

IUPAC system

To systematize the nomenclature of organic compounds, IUPAC system of nomenclature was first introduced in 1947.

General Rules for IUPAC Nomenclature of Organic Compounds

The most important feature of this system is that any given molecular structure has only one IUPAC name and any given IUPAC name denotes only one molecular structure.

The IUPAC name of any organic compound essentially consist of three parts ,i.e.

(1) word root

(2) suffix

(3) prefix

Word root

It denotes the number of carbon atoms present in the parent chain (the longest possible continuous chain of carbon atoms including the functional group and multiple bonds) of the organic molecule.

Chain Length Word Root
C1 Meth
C2 Eth
C3 Prop
C4 But
C5 Pent
C6 Hex
C7 Hept
C8 Oct
C9 Non
C10 Dec
C11 Undec
C12 Dodec

Suffix

There are two types of suffix :

(1) Primary suffix

A primary suffix is always added to the word root to indicate whether the carbon chain is saturated or unsaturated.

The three basic primary suffixes are :

Type of carbon chain Primary suffix General name
Saturated -ane Alkane
Unsaturated with one double bond -ene Alkene
Unsaturated with one triple bond -yne Alkyne

If the parent chain contains two, three, four or more double or triple bonds ,numerical prefixes such as di, tri, tetra are added to the prefect primary.

Type Of carbon chain Primary Suffix General name
Unsaturated with two double bonds -diene Alkadiene
Unsaturated with two triple bonds -diyne Alkadiyne

 

Examples of word root and primary suffix

(2) Secondary suffix

A secondary suffix is then added to the primary suffix to indicate the nature of the functional group present in the organic compound.

Class of Organic compound Functional Group Secondary Suffix
Alcohols -OH -ol
Aldehydes -CHO -al
Ketones -CO -one
carboxylic acid -COOH -oic acid
Acid amides -CONH2 -amide
Acid chloride -COCl -oyl chloride
Esters -COOR alkyl oate
Nitriles -CN nitrile
Thiols -SH thiol
Amines -NH2 amine

While adding the secondary suffix to primary suffix ,the terminal e of the primary suffix is dropped if the secondary suffix begins with a vowel but is retained if the secondary suffix begins with a consonant.

 

word root, primary suffix, secondary suffix examples

(1) Locants are placed immediately before the part of the name to which they relate.

For Example :  But-2-ene , Propan-2-ol

(2) The locant 1 is often omitted when there is no ambiguity.

CH3CH2CH2NH2 Propane-1-amine is often named as Propamine.

ClCH2CH2OH 2-Chloroethan-1-ol is often named as 2-Chloroethanol

CH3CH2CH2CHO Butan-1-al is often named as 2-Chloroethanol.

Prefix

There are two types of prefixes:

(1) Primary Prefix

A primary prefix is used simply to distinguish cyclic from acyclic compounds.

For example : In case of carbocyclic compounds, a primary prefix, cyclo is used immediately before the word root.

cyclopentane

Cyclopentane

Cyclo(Primary prefix) + Pent (word root) + ane( Primary suffix)

(2) secondary prefix 

Certain groups are not considered as functional groups but instead are treated as substituents. These are called secondary prefixes and are added immediately before the word roots in alphabetical order to denote the side chain or substituent groups.

The secondary prefixes for some groups which are always treated as substituent group are given below:

Substituent Group Secondary group Substituent Group Secondary Prefix
-F  Fluoro  OCH3(OMe)  Methoxy
-Cl  Chloro  -OC2H5(-OEt)  Ethoxy
-Br  Bromo  -CH3(-Me) Methyl
-I  Iodo  -C2H5(-Et)  Ethyl
-NO2  Nitro  -CH2CH2CH3(n-Pr)  n-Propyl
 Diazo group  Diazo  -C(CH3)3 tert-Butyl
 —NO  Nitroso  -CH(CH3)2(-iPr)  Isopropyl

 

IUPAC name of an organic compound consist of:

Secondary prefix + Primary prefix + Primary suffix + Secondary Suffix

Organic compound Secondary Prefix Word Root Primary Suffix IUPAC name
CH3CH2Br Bromo eth ane Bromoethane
CH3NO2 Nitro meth ane Nitromethane
C2H5OC2H5 Ethoxy eth ane Ethoxyethane
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Filed Under: Chemistry, Class 11, Organic Chemistry - Some Basic Principles and Techniques Tagged With: 3 basic primary suffix, IUPAC system, Nomenclature, prefix, primary prefix, primary suffix, rules for IUPAC Nomenclature of organic compounds, secondary prefix, secondary suffix, suffix, Trivial or common name, word root

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