Alkenes are hydrocarbons that have double bonds between carbon atoms and therefore are called unsaturated substance. The generic formula is CnH2n. The simplest alkene is ethene (also known as ethylene):
Alkenes are relatively stable compounds, but are more reactive than alkanes.
Obtainment of alkene
Mainly by cracking reaction of an alkane.
alkane → light alkane + alkene
here is an example with ethylene :
CH2=CH2 + H2 → CH3-CH3
In the case of alkene, halogenation is an addition reaction.
CH2=CH2 + Cl2 → ClCH2-CH2Cl
It's also a reaction of addition, an electrophilic addition.
δ+ δ- δ+ δ-CH3-CH=CH2 + H-Cl → CH3-CH-CH3
- Slow step : this step determine the velocity of the reaction
δ+ δ-CH3-CH=CH2 + H+ → CH3-CH+-CH3
- Fast step :
CH3-CH+-CH3 + Cl- → CH3-CH-CH3
here is the case of the ethylene
- Activation step
RO - OR → 2 RO*
- Initiation step
RO* + CH2=CH2 → ROCH2-CH2*
- Propagation step
ROCH2-CH2* + n CH2=CH2 → RO(CH2-CH2)n-CH2-CH2*
- Breaking step
R* + *R → R-R
Oxydation reactions : ozonolysis reaction
Oxydation reactions : arranged oxydation
Oxydation reactions : brutal oxydation