A-Level Chemistry: Alkenes Syllabus

Summary: The A-level alkene syllabus mainly covers structure and bonding, E/Z isomerism, electrophilic addition reactions, bromine-water testing, and addition polymerisation.

1. What alkenes are

Alkenes are unsaturated hydrocarbons with a C=C double bond.
You are expected to know their general formula, commonly CₙH₂ₙ for simple acyclic alkenes.
The double bond is described in terms of σ and π bonding, and the π bond causes restricted rotation.

2. Shape and isomerism

You may need to explain the trigonal planar arrangement around the C=C bond.
Many exam boards include stereoisomerism, especially E/Z isomerism and sometimes cis-trans as a special case.

3. Reactions of alkenes

This is usually the largest part of the topic. You normally study addition reactions, especially:

with hydrogen → alkanes
with halogens → dihalogenoalkanes
with hydrogen halides → halogenoalkanes
with steam → alcohols
sometimes oxidation to diols using acidified potassium manganate(VII)

4. Mechanisms

You are usually expected to learn electrophilic addition.
You should know what an electrophile is.
You should be able to draw the mechanism using curly arrows.
You should understand how heterolytic fission forms ions.
You may need to predict major and minor products for unsymmetrical alkenes using carbocation stability or Markovnikov’s rule.

5. Tests for alkenes

You should know the test for a C=C bond using bromine water or bromine.
A positive result is decolourisation.

6. Polymerisation

Most boards include addition polymerisation of alkenes.
You may need to draw the repeat unit.
You may need to work backwards from a polymer to the monomer.
You should understand why addition polymers are often unreactive.
Common examples include PVC / poly(chloroethene).

7. Environmental and industrial ideas

Some specifications also include recycling and disposal of polymers.
This may include incineration, energy recovery, and biodegradable polymers.
You may also need to understand the sustainability of polymer use.

8. Practical work

Typical practical work includes testing for unsaturation using bromine water.
Some boards also mention making an addition polymer such as poly(phenylethene).