Initially, there was no proper system for the naming of compounds. Mostly there were trivial names that were used depending upon the country and region. These trivial names were based on the discoverer or the nature of the compound or its place of discovery. The system of trivial names was not standard and led to much confusion, thus raising the need for a standard system for the naming of organic compounds. IUPAC came up with a set ofrulesthat are used universally for the naming of organic compounds.
There are two names associated with every compound:
- Common name – It is different from trivial name in the sense that it also follows a rule for its nomenclature.
- IUPAC name
Rule of nomenclature
- Find the longest carbon chain.
- Number the longest carbon chain such that the carbon atom(s) to which the halogen(s) is/are attached get the lowest number(s).
- Multiple halogen atoms are labeled with the Greek numerical prefixes such as di, tri, tetra, to denote the number of identical halogen atoms attached to a carbon atom. If more than onehalogen atoms attached to the same carbon atom, numeral is repeated that much time.
- In case, different types of halogens are attached, they are namedalphabetically.
- Position of halogen atom is indicated by writing the position and name of the halogen just before the name of the parent hydrocarbon.
Methodology of writing name
- First of all write the root word for the parent hydrocarbon (depending upon the no. of carbon atoms in the longest carbon chain).
- Secondly, calculate the number of halogen atoms present. If there are multiple halogen atoms present, then arrange the halogens alphabetically in prefix, labeling them with their respective positions. But, if same halogen atom is present more than once then use the prefixes di, tri, tetra etc.
Nomenclature of Haloalkanes
- General common name of haloalkane is “Alkyl halide”.
- General IUPAC name for haloalkane is “numerical position – alphabetically arranged halo – rootword – ane”.
Nomenclature of Haloarenes
- General common name of haloarene is “aryl halide”. If more than one halogen atom is present thenprefixes o-,m-, p- are used.
- General IUPAC name of haloarene is also “aryl halide”. But in IUPAC naming, for multiple halogen derivatives the aromatic ring is numbered and each halogen atom is named with its numerical position in the ring.
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