Formula of alkene :
CnH2n
Nomenclature
all alkanes begin with the prefix as mentioned below and ending with -ene
there is no methene ( 1 carbon )
(2 carbon atoms ) eth-
( 3 carbon atoms ) prop-
( 4 carbon atoms ) but-
( 5 carbon atoms ) pent-
( 6 carbon atoms ) hex-
( 7 carbon atoms ) hept-
( 8 carbon atoms ) oct-
( 9 carbon atoms ) non-
(10 carbon atoms ) dec-
Properties of alkene
1) Combustion
Burns in plentify supply of air, it produces carbon dioxide and water.
If INCOMPLETE COMBUSTION, it gives soot, carbon monoxide, carbon dioxide and water.
2) Hydrogenation
C2H4 + H2 ---> C2H6 (ethane)
3) Bromination
C2H4 + Br2 ---> C2H4Br2
** This is bromine test: used to distinguish between alkane and alkene ** ( Typical Structure Question!)
Alkene: Aqueous bromine will decolourised.
Alkane: Aqueous bromine remains unchanged.
4) Hydration
C2H4 + H2O ---> C2H5OH (ethanol)
Another method to prepare ethanol is 'fermentation'
C6H12O6 ---> 2 C2H5OH + 2 CO2
Conditions: yeast and temperature: 25'C.
5) Cracking
To break less useful linger chains into smaller useful fractions.
Conditions: 400°C - 700°C , silicon dioxide /aluminum oxide as catalyst.
