Alkenes

go back

• Unsaturated hydrocarbon
• Has a double bond
• General formula: $C_n{H}_{2n}$

Geometrical Structural Isomers

• There is no rotation possible around a double bond
• 2 molecules can form where the position of the double bond remains the same but the spatial arrangement across the double bond is different
• Cis isomer: CH3 groups are on the same side of the double bond
• Trans isomer: CH3 groups are on opposite sides of the double bond

Criteria

• Double Bond between carbons (C=C)
• 2 different groups attached

Chemical Properties

Addition reactions

1. Hydrogenation (*$+H_2$)
   1. Saturation
   2. Alkene + $H_2$ $\to$ alkane
   3. Conditions:
      1. Catalyst (Nickel)
      2. High temperature and pressure
2. Halogenation ($+C{l}_2/B{r}_2/I_2$)
   1. Alkene + halogen $\to$ alkane with new functional group
   2. Test for alkene double bond
   3. $B{r}_{2(aq)}$ is bromine water, orange solution
      1. Colourless gas bubbled through orange solution, orange solution decolourises
      2. Condition: catalyst is kinetic energy, i.e. shaking the solution
         1. Technically happens readily
3. Reaction with hydrogen halide (HCl, HBr, HI)
   1. Alkene + hydrogen halide $\to$ halo-alkane
4. Hydration ($+H_{2}O$)
   1. Alkene + water $\to$ some sort of alcohol
   2. BRAZILLLLLLLLL (pilling reference, you wouldn’t get it)c
   3. Conditions:
      1. Catalyst (Phosphorous acid)
      2. high temperature and pressure