NOMENCLATURE OF SIMPLE ORGANIC COMPOUNDS
Key to naming: Prefix+root word+suffix
Where, prefix: substituent
Root word: parent chain and no. of carbon atoms in it
Suffix: functional group
But some of the functional groups are treated as substituents and are written like Halo-, cyano- etc.
For Straight chain hydrocarbons
The name is based on the chain str. of the compound. Suffix is “ane” for alkanes, “ene” for alkene and “yne” for alkyne.
Prefix indicationg the no. of carbon atoms is given:
For branched chain hydrocarbons
First of all, a perent chain is decided that is the longest carbon chain of the molecule. It should contain the max. no. of carbon atoms amongst all chains. e.g. I is the correct way of numbering, not II.
If there are two/more chains of same no. of carbon atoms, then chain with max. no. of sustituent/branches is considered the parent chain.
The numbering is done in such a way that the branches get the lowest possible numbers. These branches or small chains are called alkyl groups. The names of these groups are written as prefix. An alkyl group is the alkane minus one hydrogen atom and it is named by substituting ‘ane’ of alkane by ‘yl’. e.g –CH3 – Methyl, -CH2CH3 – Ethyl etc.
These substituents can be branched also and these are named as trivial names. E.g.
If the same alkyl group occurs more than once as a side chain, we indicate this by the prefix di-, tri-, tetra-, etc., to show how many of these alkyl groups there are, and indicate by various numbers the positions of each group. Ex- 2,2,4-trimethylpentane.
Carbon atom of the branch that attaches to the parent chain is numbered 1.