Nomenclature of organic compounds

Method of naming organic compounds developed by IUPAC (International Union of Pure and Applied Chemistry).

It’s called IUPAC system of nomenclature.

Naming the organic compounds:

1. Identify the parent chain

2. Identify the functional group

3. Accordingly add prefixes or suffixes.

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

(i)   Root word        (ii)   Suffix         (iii) Prefix

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

(i) 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
C1	Meth-
C2	Eth-
C2	Prop-
C4	But-
C5	Pent-
C6	Hex-
C7	Hept-
C8	Oct-
C9	Non-
C10	Dec-

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

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

(iii) Secondary Suffixes:

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-
Carboxylic 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

Example:

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