Nomenclature of Hydrocarbons

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Nomenclature is the system of naming. With the existence of innumerable compounds of carbon, it has become necessary to follow a universal, rational system of naming. Such a system has been evolved by International union of pure and applied chemistry (IUPAC). By following this system, we can eliminate the confusion that arises due to usage of common names or trivial names.

Nomenclature of straight chain hydrocarbons

The IUPAC name of a straight chain hydrocarbon is divided into two parts:

i. Word root

ii. Suffix

Word root

Word root determines the number of carbon atoms in the compound. The word roots for compounds having five or more carbon atoms are derived from Greek numbers.

Chain length	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10
Word root	Meth -	Eth -	Prop -	But -	Pent -	Hex -	Hept -	Oct -	Non -	Dec -

 

Suffix

To determine the nature of the bond (single, double or triple) between the carbon atoms, primary suffixes are used.

Hydrocarbon	Primary suffix	General name
Saturated C – C	- ane	Alkane
Unsaturated C = C	- ene	Alkene
Unsaturated C ≡ C	- yne	Alkyne

 

Nomenclature of saturated hydrocarbons (alkanes)

In the IUPAC nomenculature, alkanes end with '-ane'

Condensed Formula	Word root	Primary suffix	IUPAC name and Formula
1. CH4 2. CH3CH3 3. CH3CH2CH3 4. CH3CH2CH2CH3 5. CH3CH2CH2CH2CH3	Meth - Eth - Prop - But - Pent	- ane - ane - ane -ane - ane	Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10 Pentane C5H12

 

 

Nomenclature of unsaturated hydrocarbons

Alkenes

In the IUPAC nomenclature, alkenes end with '-ene'

Condensed Formula	Eord root	primary suffix	IUPAC name and Formula
1. CH2 = CH2	Eth -	- ene	Ethene C2H2
2.CH3 - CH = CH2	Prop -	- ene	Propene C3H6
3.CH3 - CH2  - CH = CH2	But -	- ene	Butene C4H8
4.CH3 - CH2  - CH - = CH2	pent -	- ene	Pentene C5H10

 

Alkynes

In the IUPAC nomenculature, alkenes end with '-yne'.

Condensed Formula	Word root	Primary Suffix	IUPAC name and formula
CH ≡ CH	Eth -	- yne	Ethyne  C2H2
CH3 - C ≡ CH	Prop -	- yne	Propyne  C3H4
CH3 - CH2 - C ≡ CH	But -	- yne	Butyne  C4H6
CH3 - CH2 - CH2 - C ≡ CH	Pent -	- yne	Pentyne  C5H8