R-AECHE-42

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Alkenes: unsaturated hydrocarbons, containing a single double bond between Carbon atoms
- Higher ratio of carbon to hydrogen
- More double bonds means its not a alkene.
Hydrocarbons: containing hydrogen and carbon only
Unsaturated: indicates the presence of a double or triple bonds

Alkenes start with ethene. It is trigonal planar.

Structural isomers only apply for molecules of the same homologous series!!!! e.g.

methylpropene, but-1-ene, and but-2-ene are all structural isomers for n-butene.
Cyclobutane has the same molecular formula, but is not a structural isomer for n-butene.

Chemical Properties of Alkenes:

Alkenes undergo specific type of reaction called addition reactions.
In substitution, you get 2 unique products.
In Addition, the general formula is $A + B \rightarrow C$
Thus, they are very important type of organic compounds for organic synthesis.
In alkenes hybridisation is $sp^2$.
Alkenes connect pi bonds, which are very weak, which is why alkenes are so reactive.
Halogenation occurs between alkenes and ($Cl_2,Br_2,I_2$)
- $Br_2$ is the best test for double bond (alkenes)
- $Br_{2(aq)}$ is bromine water, an orange solution
For example, for propene ($C_3H_6$),
- $C_3H_{6}+ Br_{2}\rightarrow C_3H_6Br_2$
- Propene is added to aqueous bromine, producing 1,2-dibromopropane
- Orange solution added to colourless gas producing a colourless liquid.
  - May not be gas! Large molecules can be liquid.
- $C_3H_{6}+ HCl_{(g)} \rightarrow C_3H_7Cl$
- Propene is added to hydrogen chloride, producing 2-chloropropane
  - Markovnikov's rule states that 1-chloropropane would be a minor product of this reaction.
- Many important industrial reactions:
  - $+H_2$ (hydrogenation) condition: Nickle catalyst for industrial processes
    - Catalyst reduces requirement for temperature and pressure