ALKENES:
Alkenes are unsaturated hydrocarbons which contain a carbon-carbon double bond.
They can be represented by the general formula CnH2n.
Why alkenes are called olefins?
They are also known as 'olefins', derived from Latin word 'oleum' meaning 'oil' and 'ficare' meaning 'to form', because their lower members form oily layer on treatment with chlorine and bromine.
Rules for Nomenclature and Alkenes: ( IUPAC)
Following are the some rules
1. Select longest continuous chain of carbon atom as a parent chain containing double bond.
2. Name of compound must end on ene .
E.g ethene propene etc
3.Give double bond least possible number.
4.Substiutnt name is always written before parent name.
5.Position of double bond must be mentioned.
6.Position of substituent must be mentioned before name
7.If more then one similar type of substituents are present we will use the term di For 2 Tri for 3
Tetra for 4
8.If different type of substituents are present we will follow alphabatical order .
9.If more then one double bonds are present we will use the term diene for 2 double bonds and triene for 3 double bonds
Examples
1 2 3 4 5 6 CH3-CH=CH-CH2-CH2-CH3 2- Hexene
CH3 | CH3-CH=C-CH-CH2-CH3
3-Methyl-2-Hexene
1 2 3 4 5 6
CH3-CH=CH-CH=CH-CH3 2,4-Hexadiene