Nomenclature of Organic compounds

The systematic process of assigning an accurate name to a particular organic compound on the basis of scientific rules is known as nomenclature (naming of an organic compound). According to IUPAC nomenclature, the name of an organic compound consists of a prefix, word root, and suffix.

Introduction

The systematic process of assigning an accurate name to a particular organic compound on the basis of scientific rules is known as nomenclature (naming of an organic compound).

There are two types of naming system. They are-

• Trivial (traditional) or common system of nomenclature -In the early stages of development of the organic compound, there was no any scientific method of naming organic compounds. The organic compounds were named by knowing the sources from where they were obtained. Like, Methane (CH₄) was named marsh gas because it was produced in marshy(damp) places. Similarly, formic acid (HCOOH) was named because it was found in red ants (Formica) etc.
• IUPAC system of nomenclature - In order to rationalise the system of nomenclature, an International Congress of Chemistry (ICC) was held at Geneva in 1892 and a systematic method, known as Geneva system was developed. The Geneva system was further revised from time to time for the betterment of naming system and it was extended to International Union of Chemistry (IUC) in 1930. The continuation of the effort of various chemists led to the development of the IUPAC (International Union of Pure and Applied Chemistry) system.

Naming according to the IUPAC rules-

According to IUPAC nomenclature, the name of an organic compound consists of three parts-

• Wood root-

It is the basic unit of the name. It tells us the number of carbon atoms in the principal chain. For chains containing one to four carbon atoms, special word roots are used. These special word roots are derived from the common names of the corresponding alkanes. For chains containing five or more carbon atoms Greek numerals are used. The below table shows naming up to the 12^th carbon atoms-

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-

Suffix tells us about the functional groups present in the compound. The suffix may be of two types-

1. Primary suffix (1º)
2. Secondary suffix (2º)

⇒Primary suffix:The primary suffix tells us about the linkage between the carbon atoms. The primary suffix denotes the number of covalent bonds between the carbon atoms. The suffix used on various cases are-

⇒Secondary suffix:The secondary suffix tells us about the characteristic functional group present in the organic compound. It is added to the name, after the primary suffix. Some common secondary suffixes are given below-

Functional group	Suffix
Alcohol (-OH)	-ol
Thioalcohol (-SH)	-thiol
Aldehyde (-CHO)	-al
Ketone (>C=O)	-one
Carboxylic acid (-COOH)	-oic acid
Ester (-COOR)	-oate
Acid halide (-COX)	--oyl halide
Amide (-CONH2)	-amide
Acyl group (RCO-)	-oyl
Cyanide (-C≡N)	-nitrile
Amine (-NH2)	-amine
Sulphonic acid (-SO3H)	-sulphonic acid

When using these secondary suffixes, the carbon of the functional group (if any) is counted in the principal chain.

• Prefix-

A prefix indicates the substitution of other atoms or groups (not regarded as principal functional groups) in place of hydrogen atoms in the main chain of carbon atoms. Most commonly used prefixes are alkyl groups. Some of the prefixes are given below-

Substituent	Prefix
CH3-	Methyl-
C2H5-	Ethyl-
F-	Fluoro-
Cl-	Chloro-
Br-	Bromo-
I-	Iodo-
CH3CH2CH2-	Propyl-
-NO2	Nitro-
-OR	Alkoxy-
-N=N-	Diazo-
-N=O	Nitroso-

Hence, a complete representation of IUPAC name of a compound is given by the formula -

Prefix + word root + primary suffix + secondary suffix