Alkenes are hydrocarbons with a C=C double bond – this is an example of a functional group, the part of the molecule that makes it different to an alkane and is responsible for the types of reactions it undergoes.
There is a huge amount of new chemistry here but from stereoisomers to reaction mechanisms and polymerisation, we’ve got you covered 😊.
Stereoisomerism and the Cahn, Ingold, Prelog rules
Alkenes cannot rotate through their C=C double bond, it locks the structure of the molecule in place at that point.
If we have different groups bonded to the carbon atoms either side of the double bond, we have pairs of stereoisomers.
Find out how to name them here.
How do organic reactions actually happen?
Most reactions take place via two or three steps with short-lived, unstable, intermediate ions bridging the steps from reactants to products.
A reaction mechanism shows the details – bonds breaking, new bonds forming and the movements of electrons.
Get your head around all the terminology you are going to need to know!
Stabilising carbocations through inductive and mesomeric effects
Inductive and mesomeric effects both play an important role in determining how organic reactions happen through their abilities to stabilise carbocation intermediates.
Understanding the difference between sigma and pi bonds
If we can explain how it is that carbon can make four bonds by hybridising its 2s and 2p orbitals, we can explain the unique features of single and double bonds in alkenes …
Electrophilic addition reactions in alkenes (1)
An introduction to the reaction mechanism …
Electrophilic addition in alkenes (2) – the bromine water test
The classic test for an alkene is to shake your sample with orange bromine water, and if the molecule contains a C=C double bond the bromine water is decolourised, but could you draw the mechanism?
Electrophilic addition in alkenes (3) – reaction with water to form an alcohol
The reaction of an alkene with water to from an alcohol is an example of a hydration reaction.
Find out how to draw the mechanism here.
Elimination reactions – dehydrating an alcohol
If we dehydrate an alcohol, we are essentially removing a water molecule and the product will be an alkene.
The type of reaction is elimination.
Addition polymers and their properties
Polymers are long chain molecules made via addition polymerisation or condensation polymerisation – the result are all the plastics, fibres and elastomers that modern life depends upon.
Making addition polymers by radical polymerisation
Understand the radical mechanism for how an addition polymer is made.