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Why do we need a nomenclature?
Organic compound names were once associated with the natural things from which they were derived. Formic acid, for example, was first obtained from 'red ants' by the distillation process.
'Formica' is the Latin name for the red ant. As a result, the name formic acid was derived from the Latin word. Organic compounds were later synthesised from sources other than natural sources.
Scientists devised a method for naming organic compounds based on their structures. As a result, the IUPAC (International Union of Pure and Applied Chemistry) developed a set of rules for chemical compound nomenclature.
Note: The International Union of Pure and Applied Chemistry (IUPAC), founded in \(1919\), is an international organisation that represents chemistry plus related sciences and technologies.
IUPAC primarily pursues these goals with the help of over \(1000\) volunteer chemists. The affiliate Member Programme, which provides a virtual channel of global communication, has nearly \(5000\) chemists enrolled. The International Union of Pure and Applied Chemistry (IUPAC) is recognised as the international authority on chemical nomenclature, terminology, symbols, units, atomic weights, and related topics.
Components of an IUPAC name:
Organic compounds on naming with IUPAC consist of \(3\) parts:
- Root word
- Prefix
- Suffix
These three components are combined in the following order to yield the IUPAC name of the compound.
\(\text{Prefix + Root word + Suffix → IUPAC Name}\)
1. Root word:
- It is the fundamental unit that describes the carbon skeleton.
- It specifies the number of carbon atoms in the compound's parent chain as well as the pattern of their arrangement.
- The majority of the names are derived from Greek numerals based on the number of carbon atoms present in the carbon skeleton (except the first four).
- The root words for the parent chain of hydrocarbons containing \(1\) to \(10\) carbon atoms as shown in the below table.
Root words of hydrocarbons:
Number of carbon atoms | Root word |
\(1\) | Meth- |
\(2\) | Eth- |
\(3\) | Prop- |
\(4\) | But- |
\(5\) | Pent- |
\(6\) | Hex- |
\(7\) | Hept- |
\(8\) | Oct- |
\(9\) | Non- |
\(10\) | Dec- |
2. Prefix:
- The prefix represents the substituents or branches in the parent chain.
- Atoms or groups of atoms other than hydrogen are known as substituents present in the parent chain of the carbon structure.
- The below table lists the major substituents and the prefixes that are used for organic compounds:
Prefix for IUPAC Name:
Substituent | Prefix used |
\(-F\) | Fluoro |
\(-Cl\) | Chloro |
\(-Br\) | Bromo |
\(-I\) | Iodo |
\(-NH_2\) | Amino |
\(-CH_3\) | Methyl |
\(-CH_CH_3\) | Ethyl |
3. Suffix:
- The suffix forms the end name.
- It is further divided into two sections.
(a) Primary suffix: The primary suffix follows the root word. It represents the nature of the parent chain in carbon to carbon bonding.
If all of the bonds between the parent chain's carbon atoms are single, the suffix 'ane' must be used.
The suffixes ‘ene' and ‘yne' are used for compounds with double and triple bonds, respectively.
(b) Secondary suffix: The compound's functional group is described by the secondary suffix.
Suffix for IUPAC Name:
Class of the compound | Functional group | Suffix used |
Alcohol | \(-OH\) | -ol |
Aldehyde | \(-CHO\) | -al |
Ketone | \(-C=O\) | -one |
Carboxylic acid | \(-COOH\) | -oic acid |
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