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Nomenclature of Simple Organic Compounds

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

  • Position of the substituent and functional groups is given by giving the carbon no. on which it is present just before the prefix and suffix for that particular substituent and functional group.

  • If there is more than one substituent present, then the prefixes are written in alphabetical order.

  • If two substituents are present on equivalent position then the lower no. is given to the one coming first in alphabetical order.

  • if there are more than one functional group present, then the compound is named after the functional groups which is of highest priority (order of priority is given by IUPAC) and numbering on parent chain is done on such way that the principal functional group gets the lowest possible no. The rest of the functional groups are treated as substituents and written as prefixes. E.g.

But some of the functional groups are treated as substituents and are written like Halo-, cyano- etc.

e.g. 2-chloropropane

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:

1 Meth

2 Eth

3 Prop

4 But

5 Pent

6 Hex

7 Hept

8 Oct

9 Non

10 Dec

20 Icos

30 Tricos

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.

Example:


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