how we give IUPAC name to compounds

According to the IUPAC system, the name of an organic compound consists of three parts:

1. Root word
2. Suffix
3. Prefix

 

Root Word:

It depends on the number of carbon atoms present in the longest carbon chain selected.

 

Number of carbon atoms	Root word
One carbon atom           C1	Meth
Two carbon atoms           C2	Eth
Three carbon atoms        C3	Prop
Four carbon atoms          C4	But
Five carbon atoms           C5	Pent
Six carbon atoms             C6	Hex
Seven carbon atoms        C7	Hept
Eight carbon atoms          C8	Oct
Nine carbon atoms           C9	Non
Ten carbon atoms         C10	Dec

 

Suffix:

The root word is followed by an appropriate suffix which represents the nature of the bond in a carbon–carbon atom.

 

Nature of bond	Suffix	General name	General formula
Single bond (C–C)	-ane	Alkane	CnH2n+2
Double bond (C=C)	-ene	Alkene	CnH2n
Triple bond ( )	-yne	Alkyne	CnH2n−2
Group (R-)	-yl	Alkyl	CnH2n+1

 

Prefix:

It denotes the substituent, alkyl or functional group and its position in the carbon chain.

Di-, tri- and tetra- are used for two, three and four groups of the same type, respectively.

In naming an organic compound, the following simple rules are followed:

1. Selection of carbon chains: The longest continuous chain of ‘C’ atoms, known as parent chain, is selected. The longest chain need not be straight. For example:

 

Here, the longest chain is of 7 carbon atoms, so the root word is ‘hept’, the remaining carbon atoms are substituents.

 

2. The branch chains are considered substituents, and their positions are indicated by the number of carbon atoms to which they are attached.

  For example:

 

3. The carbon atoms of the longest chain are numbered in such a way that the alkyl groups get the smallest possible number.

For example:

 

4. In case, any functional group is present in the chain, the carbon atoms are numbered in such a way that the functional group gets the smallest possible number.

For example:

5. In case, different types of substituents are attached to the chain, they are arranged and named alphabetically.

 

 2,Bromo,4 chloro hexane

 

6. The positions of alkyl groups are indicated by writing the position and name of the alkyl group just before the name of the parent hydrocarbon.

 

 

                       3-ethylheptane

 

7. Multiple alkyl groups are labeled with the Greek numerical prefixes such as ‘di’ for two, ‘tri’ for three, ‘tetra’ for four, ‘penta’ for five.

    If two alkyl groups are on the same carbon atom, then the numeral is repeated.