1. Reactions of Alkenes

2. Saturated hydrocarbons (alkanes) reacted by substitution, whereas the reaction of unsaturated hydrocarbons (alkenes) is by addition to the double bond

3. Addition Reactions 1. Hydrogenation – addition of H2
- uses a heavy metal catalyst (Pt, Pd, or Ni) to add to the double bond
- the double bond breaks and the alkene is converted to an alkane
-both hydrogens are added from the same side (cis) of the double bond

4. Hydrogenation Examples
1. Hydrogenate ethene.
2. Hydrogenate 1,2-dimethylcyclopentene.

5. 2. Halogenation - addition of Cl2 or Br2
- this will always be a trans addition
Ex.; 1. Halogenate (chlorinate) ethene.
2. Brominate cyclopentene.

6. Bromine with CCl4 reddish solution
NOTE: The addition of bromine is used as a qualitative test to see if a compound is saturated or unsaturated.
Bromine with CCl4 reddish solution
Add this to a compound, if the red color persists, the compound is saturated (an alkane)
If the red color disappears, the compound is unsaturated (an alkene)

7. Using Unsymmetrical Reagents
Unsymmetrical reagents have two or more different atoms adding to the bond
Ex.; H-OH, H-Br, H-Cl, H-HSO4, CH2=CH-CH3, etc.
These follow Markownikoff’s Rule, which says when an unsymmetrical reagent adds to an unsymmetrical double bond, the positive part (usually the hydrogen) becomes attached to the double bonded carbon atom that has the greater number of hydrogens

8. 3. Hydration – addition of water (H-OH)
-this requires the presence of an acid catalyst and yields an alcohol as the product
Ex.; Hydrate propene.

9. 4. Hydrohalogenation - addition of HI, HBr, HCl
Ex.; 1. React propene with hydrochloric acid.
2. React 2-pentene with hydrobromic acid.

10. This works for any of the previous reagents
5. 1,4 Addition – when two double bonds are separated by a single bond, they are said to be conjugated
Ex.; CH2=CH-CH=CH2
Addition will occur at the 1 and 4 positions relative to the double bond, and the double bond moves to the 2,3 position
This works for any of the previous reagents
Ex.; Brominate 1,3-butadiene

11. 6. Oxidation - alkenes are readily oxidized, whereas alkanes are not
KMnO4 – potassium permanganate is the oxidizing agent; it changes from purple to brown indicating it was reduced and the alkene was oxidized
This is known as the Baeyer test – distinguishes alkanes (purple) from alkenes (brown)
The product depends on what type of alkene you start with
It is also a temperature dependent reaction

12. Oxidation Examples 1. 2. 3.
KMnO4 Δ

13. Oxidation Example – Temp. Dependent4.
KMnO4
0°C

14. 7. Ozonolysis - reaction with ozone (O3)
Ozone is prepared by passing an electric charge through oxygen
Reacts rapidly with alkenes to give an aldehyde or a ketone
Breaks the alkene into two fragments at the double bond, each of which has an oxygen atom doubly bonded to the original alkene carbons
Used primarily to locate the position of a double bond

15. Ex; 1. react 1-butene with ozone.
2. React 2-butene with ozone. How is this reaction different than the first example