All their names end in ene, which means DOUBLE BOND. The other atoms present may be Hydrogen, Chlorine, Bromine, Fluorine, Iodine. Except for hydrogen, these atoms have their own organic names:
Here is an example of an alkene.
Notice the carbon chain in RED, and that there is a DOUBLE BOND between two of the carbons.
We say that the DOUBLE BOND is at carbon 2.
TWO chlorine atoms are added in as well.
5,5-dichloro-pent-2-ene
How do you name ALKENE compounds?
The method is similar as in naming alkanes, but you must indicate the POSITION of the DOUBLE BOND.
Step 1
Then the road is 5 carbons long.
Now 5 carbons = pent
Notice that the numbering starts closer to where the double is, and not from where the chlorine is located.
Step 2
The DOUBLE BOND is at carbon number 2.
Hence we say 2-ene.
We combine pent and 2-ene.
Hence the road name is pent-2-ene.
Step 3
Now the chlorine atoms are found at carbon 5 and 5
We call it 5,5-dichloro
(di means 2 atoms)
We combine all the words into one big word!
Hence the name is:
5,5-dichloro-pent-2-ene
Another example
4-bromo-1-choro-but-1-ene
"Main road" is but-1-ene
Notice that the numbering starts from the side closer to the double bond.
There is a 4-bromo and a 1-chloro.
These are written in alphabetical order.
4-bromo-1-choro-but-1-ene