Alkenes

• Alkenes are unsaturated hydrocarbons.
• They have at least 1 double covalent bond. They can undergo addition reactions.
• Double bonds have a high electron density, making alkenes fairly reactive.
• Alkenes are attacked by electrophiles due to their double bonds
• Electrophiles are electron pair acceptors. They are deficient in electrons and are attracted to the double bond.
• Reacting hydrogen halides with unsymmetrical alkenes produces two different products.
• The amount of the two products is determined by the stability of the carbocation intermediate.
• The more alkyl groups bonded to the carbocation the more stable the intermediate is.
• This is due to the positive inductive effect, as the alkyl groups push electrons towards the carbocation which stabilises it.
• The more stable the carbocation, the more likely it will form.
• Alkenes react with cold, concentrated sulfuric acid to form alkyl hydrogen sulphates.
• H2SO4 is used as a catalyst in making an alcohol from an alkene.
• The alkyl hydrogen sulphate formed is then used to make an alcohol.
• To form the alcohol, add water and warm. This is called hydrolysis.
• From the reaction of making alcohol from the alkyl hydrogen sulphate intermediate, sulfuric acid is reformed.
• Alkenes are monomers which join to form addition polymers.
• Polymers can be natural (e.g. protein) or synthetic (e.g. poly(ethane)).
• Poly(alkenes) are saturated, like alkanes, normally non-polar and hence unreactive.
• Most polyalkenes only have van der waals forces, the longer and more closely packed the chains are, the more van der waals forces and thus the stronger the polymer is.
• Some polyalkenes have halogens. They can form stronger dipole-dipole forces and so have different properties.
• Plasticisers are added to polymers to change their properties. They slide between the polymer chains pushing them apart.
• Plasticisers weaken the intermolecular forces making the chains able to slide over each other and making the polymer easier to bend.