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Explain IUPAC system of nomenclature with examples.

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IUPAC System
(a) The full form of IUPAC system is International Union of Pure and Applied Chemistry.
(b) This system of nomenclature was first introduced in 1947 and was modified from time to time.
(c) The most exhaustive rules for nomenclature were first published in 1979 and later revised and updated in 1993.
The systematic IUPAC name of an organic compound consists of four parts.
1. Root word
2. Suffix(es)
3. Prefix(es)
4. Infix
The complete systematic IUPAC name can be represented as :
Prefix + Infix + Root word + 1° suffix + 2° suffix
1. Root Word : It indicates the number of carbon atoms in the longest possible continuous carbon chain also known as parent chain chosen by a set of rules. The root words used for different length of carbon chain (upto 10) are shown below :

Number of carbon atoms in the parent chain Root word
1 Meth
2 Eth
3 Prop
4 But
5 Pent
6 Hex
7 Hept
8 Oct
9 Non
10 Dec

2. Suffix : It is again divided into two types:
(i) Primary suffix, and
(ii) Secondary suffix.
(i) Primary Suffix : It is used to indicate the degree of saturation or unsaturation in the main chain. It is added immediately after the root word.

(ii) Secondary Suffix: It is used to indicate the main functional group in the organic compound and is added immediately after the 1° suffix.

The suffixes as well as prefixes used for some important functional groups are shown in the following table in the decreasing order of their priority.

 

3. Prefix- The prefix is used to indicate the side chains, substituents and low priority functional groups (which are considered as substituents). The prefix may be added immediately before the root word or before the infix.
The prefixes used for some common side chains and substituents are shown below : (The prefixes for functional groups are already given).

Remember that the alkyl groups along with halo, nitro and alkoxy have the same preference. They have lower priority than double and triple bonds.

4. Infix: The infixes like Cyclo, Spiro, Bicyclo are added between the prefix (es) and root word to indicate the nature of parent chain.

  • The “Cyclo” infix is used to indicate the cyclic nature of the parent chain.
  • The “Spiro” infix is used to indicate the spirocycto compound.
  • The “Bicyclo” infix is used to indicate the bicyclic nature of the parent chain.
  • The infixes are sometimes called as primary prefixes.

Steps for Writing IUPAC Name

  1. The first step in giving IUPAC name to an organic compound is to select the parent chain and assign a root word.
  2. Next, the appropriate primary suffix must be added to the root word to indicate the saturation or unsaturation.
  3. If the molecule contains functional group or groups, a secondary suffix must be added to indicate the main functional group. This is optional and not necessary if the molecule contains no functional group.
  4. Prefix the root word with the infix “cyclo” if the parent chain is cyclic; or with the infix “spiro” if it is a spirocyceo compound; or with the infix “bicyclo” if the compound is bicyclic.
  5. Finally add prefix (es) to the name if there are side chains or substituents on the parent chain.
    Example : The IUPAC name of the following compound is arrived in steps mentioned below :

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