Alkenes - Reactions

Alkenes undergo many more reactions than alkanes. These can be used to differentiate them (tell them apart). These reactions are also useful in converting one organic compound into another.

For all of these reagents, there would be no reaction if an alkane was used instead.

Hydrogenation

Reagent: H₂

Conditions: Catalyst required (often Ni or Pd/C)

This is an addition reaction.

Oxidation

Reagent: alkaline potassium permanganate (MnO₄^-/OH^-)

Although -OH groups are added, we classify this reaction as oxidation, not "addition".

The product is called a "diol" (two alcohol groups). in this example, the name would be cyclohexane-1,2-diol.

Hydration

Reagent: dilute acid (sulfuric or phosphoric)

This is also an addition reaction:

If the alkene has three (or more) carbon atoms, there are two possible structures, depending upon which carbon atom the -OH group binds to (and, therefore, which carbon the -H atom attaches to). One product is more common (major product) than the other (minor product). Working out which is Major and which is minor is determined using Markovnikov's Rule.

Halogenation

Reagent: HX (e.g. HBr)

Much the same as hydration, this is an addition reaction, and Markovnikov's Rule usually has to be applied to these examples.