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:
- Identify the parent chain
- Identify the functional group
- 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:
\(\overset{5}{\mathop{{{H}_{3}}}}\,C-\underset{C{{H}_{3}}}{\mathop{\underset{|}{\mathop{C\overset{4}{\mathop{H}}\,}}\,}}\,-C\overset{3}{\mathop{H}}\,=C\overset{2}{\mathop{H}}\,C{{\overset{1}{\mathop{H}}\,}_{2}}OH\)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