There was no proper system for the naming of compounds initially. Mostly trivial names were used depending upon the country and region. These names used to come from the name of discoverer, the nature of the compound or its place where it was discovered. This system of naming was not standard and led to much confusion. This had raised the need for a standard system for the naming of organic compounds. IUPAC (International Union of Pure and Applied Chemistry) came up with a set of rules that are now used universally for the naming of organic compounds.
Every organic compound can be named in two ways:
- Common name – This should not be confused with trivia as common name also follows a rule for its nomenclature.
- IUPAC name
Rule of nomenclature
- The longest carbon chain in the structure should be found
- Number the longest carbon chain in such a way that the carbon atom(s) to which the halogen(s) is/are attached get the lowest number(s).
- The numerical prefixes such as di, tri, tetra, are used to label multiple halogen atoms to denote the number of identical halogen atoms attached to a carbon atom.
- Numeral is repeated multiple times when more than one halogen atoms are attached to the same carbon atom. If different types of halogens are attached to the carbon atom then they are named in alphabetical order.
- To indicate the position of halogen atom, name ad position of the halogen is written just before the name of the parent hydrocarbon.
Methodology of writing name
- Root word for the parent hydrocarbon (depending upon the no. of carbon atoms in the longest carbon chain) is written in the very first step.
- Then calculate the number of halogen atoms present. If there are multiple halogen atoms present, then by labelling them with respective positions, arrange the halogens alphabetically in prefix.
Nomenclature of Haloalkanes
- General common name used to denote haloalkane is “Alkyl halide”.
- General IUPAC name for haloalkane is written by numerically positioning and alphabetically arranging the halo – root word – ane”.
Common and IUPAC Names of some Halides
Structure Common name IUPAC name
- CH3CH2CH(Cl)CH3 sec-Butyl chloride 2-Chlorobutane
- (CH3 )3CCH2Br neo-Pentyl bromide 1-Bromo-2-2 dimethylpropane
- (CH3)3CBrtert-Butyl bromide 2-Bromo-2-methylpropane
- CH2 = CHClVinyl chloride Chloroethene
- CH2 = CHCH2BrAllyl bromide 3-Bromopropene
- CH2Cl2 Methylene chloride Dichloromethane
- CHBr3 BromoformTribromomethane
- CCl4 Carbon tetrachlorideTetrachloromethane
- CH3CH2CH2F n-Propyl fluoride1-Fluoropropane