Review of GCSE knowledge including the formation of crude oil, combustion, pollutants, alkanes and alkenes. Fractional distillation and catalytic cracking

Look at the different formulas – empirical, molecular, structural, displayed, skeletal.

Drawing and naming alkanes including structural isomers.


Drawing and naming alkanes including structural isomers.

Mechanism 1 – Free radical substitution. Alkane + halogen with UV light.

Ozone depletion and CFCs


Mechanism 2 – Nucleophilic substitution

Firstly with OH ions to make an alcohol:

Secondly with CN ions to produce a nitrile (and lengthen the chain by one carbon):

Finally, with an extra step – Ammonia to make an amine:

Mechanism 3 – Elimination:


After reviewing what we knew from GCSE, we linked alkenes to what we learned about the shapes of molecules. Although details are not needed, the tetrahedral shape of the carbons around the double bond undergo hybridisation to give us a bond angle of approximately 120° with both sigma and pi bonds as two sets of orbitals overlap to give us this double bond.

Next, we look through naming and the last part of this is identifying that there are stereo isomers and giving them a label of either E or Z.

There are plenty of mechanisms here and the next three follow an almost identical path, you can see that I simply rubbed out one group and drew in another when making these images. Firstly Electrophilic addition of HBr:

The next is the Electrophilic addition of Br2. This one is slightly more complicated as each Bromine atom has the same electronegativity so there is no natural delta charge. This is cause by the molecule’s proximity to the double bond which pushes the bonding pair further away and gives the closes Bromine a slightly positive charge. This is also the test for an alkene, it decolourise bromine water. The Bromine molecules give the water an orange colour which goes when the Bromines bond to carbons.

Alkenes will also react with Sulfuric Acid as shown below. The molecule produced is Ethyl Hydrogensulfate.

Finally, we can look at the mechanism for hydrating an alkene. Using Phosphoric Acid as a catalyst, heating to 300°C with steam, we produce an alcohol.

Remember the stability of a carbocation (C+) is critical with longer molecules. The most stable is a tertiary (3°) then a secondary (2°) and least stable is a primary (1°). The Hydrogen will add onto the side that leaves the most stable carbocation.