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Introduction

IUPAC & GOC of Class 12

Nomenclature of Organic Compounds

IUPAC System [International union of pure and applied chemistry]

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

Salient features of IUPAC system

  • A given compound can be assigned only one name.
  • A given name can clearly direct in writing of one and only one molecular structure.
  • The system can be applied in naming complex organic compounds.
  • The system can be applied in naming multifunctional organic compounds.
  • This is simple, systematic and scientific method of nomenclature of organic compounds.

Rule for Naming

Prefix (alphabetically) root word (alk) primary suffix (ene, yne) secondary suffix (main functional group)

So IUPAC name of any organic compounds essentially consists of two or three parts.

  • Root word
  • Suffix
  • Prefix

Root Words

The basic unit is a series of root words which indicate linear or continuous chains of carbon atoms. Chains containing one to four carbon atoms are known by special root words while chains from C5 onwards are known by Greek number roots.

Chain Length Root word Chain Length Root word
C1 Meth- C11 Undec-
C2 Eth- C12 Dodec-
C3 Prop- C13 Tridec-
C4 But- C14 Tetradec-
C5 Pent- C15 Pentadec-
C6 Hex- C16 Hexadec-
C7 Hept- C20 Eicos-
C8 Oct- C30 Triacont-
C9 Non- C40 Tetracont-
C10 Dec- C50 Pentacont-

In general, the root word for any carbon chain in alk-.

Primary Suffix

Primary suffix are added to the root words to show saturation or unsaturation in a carbon chain.

Nature of carbon chain Primary suffix Generic name
Saturated (C – C) -ane Alkane
Unsaturated (C = C)

with one double bond

-ene Alkene
Unsaturated (C ≡ C) with one triple bond -yne Alkyne
Unsaturated with two C = C bonds -diene Akladiene
Unsaturated with two C ≡ C bonds -diyne Alkadiyne
Unsaturated with three C = C bonds -triene Alkatriene

Secondary Suffix

Suffixes added after the primary suffix to indicate the presence of a particular functional group in the carbon chain are known as secondary suffixes.

Functional Group Secondary suffix
Alcohol (-OH) -ol
Aldehyde (-CHO) -al
Ketone (>CO) -one-
Carbonxylic acid (-COOH) -oic acid
Sulphonic (-SO3H) -sulphonic acid
Amine (-NH2) -amine
Thioalcohol (-SH) -thiol
Cyanide (-CN) -nitrile
Ester (-COOR) -oate
Amide (-CONH2) -amide
Acid halide (-COX) -oyl halide

Note:

The terminal ‘e’ of the primary suffix is removed when initial letter of secondary suffix is vowel. To illustrate the application of above basic rule, the generic names of few classes of organic compounds are given below:

Homologous series Root word Primary suffix Secondary suffix Generic name
Alcohols (saturated) Alk -ane -ol Alkanol
Alcohols (unsaturated) one double bond Alk -ene -ol Alkenol
Alcohols (unsaturated) one triple bond Alk -yne -ol Alkynol
Aldehydes (saturated) Alk -ane -al Alkanal
Ketones (saturated) Alk -ane -one Alkanone
Carboxylic acids (Saturated) Alk -ane -oic acid Alkanoic acid
Acid chlorindes (saturated) Alk -ane -oyl chloride Alkanoyl chloride

Prefix

It should always be kept in mind that alkyl groups forming branches of the parent chain are considered as side – chains. Atoms of groups of atoms such as fluoro (-F), chloro (-Cl), bromo
(-Br), iodo (-I), nitro (-NO2), nitroso (-NO) and alkoxy (-OR) are referred to as substituents. Roots words are prefixed with the name of the substituent or side chain.

Arrangement of Prefixes, Root word and Suffixes

These are arranged as follows while writing the name.

Prefix (es) + Root word + Primary suffix + Secondary suffix

For Example:

IUPAC & GOC

Prefix = Bromo (at position 3),

Root word = But,

Primary suffix = -ane

Secondary suffix = -oic acid

Hence, the name of the compound is,

3 – Bromo butanoic acid

IUPAC & GOC

Prefix = Methyl (at position 4)

Root word = Pent,

Primary suffix = -ene (at position 2),

Secondary suffix = -ol

Hence, the name of the compound is,

4 – Methyl pent – 2 – en – 1 – ol

The names of simple aliphatic organic compounds containing only straight chains atoms of various homologous series are described in table as to explain the basic rules of IUPAC system. In case of compounds. Other than hydrocarbons, only the saturated compounds have been considered.

Also Check

  1. Carbonions
  2. Free Radical
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