Chemistry AQA AS Unit 2 Alkenes

Made these notes for my year 12 summer exam to revise and read over. There are spelling mistakes in most of my files but due to the busy exam schedule I had no time to correct them (sorry).

Most files have more information than what is needed but I feel it helps you feel more confident walking into the exam if you have a greater knowledge background and may help when having to apply knowledge to questions. Good luck :)

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  • Created on: 02-09-13 13:28
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Alkenes
Unsaturated hydrocarbons
CnH2n
Planar molecules, 120
No rotation around double bonds due to the normal C ­ C bond as well as the p-orbital on
each carbon. The two orbitals overlap to form one single orbital with an electron cloud
density above and below the single bond. bond. Sometimes called a restricted rotation.
The double bond doesn't affect properties such as boiling and melting points.
V.D.W. forces are the only intermolecular forces that act between molecules. Therefore the
physical properties of alkenes and alkanes are similar.
Alkenes are non-polar hence insoluble in water.
Alkenes are more reactive than alkanes as the C=C bond forms an electron-rich area in the
molecule which can be easily attacked by electrophiles.
POSITION ISOMERS
Where functional groups differ in position on the same carbon chain.
GEOMETRIC ISOMERS
A form of stereoisomerism where they have the same structural formula but the bonds are
arranged differently in space.
Z= zame side
E= different sides
COMBUSTION
CH (g) + 3O 2CO (g) + 2HO (l)
ELECTROPHILLIC ADDITION REACTIONS:
ELECTROPHILE: An electron deficient atom, ion or molecule, which takes part in an organic
reaction by attacking areas of high electron density in another reactant.
ELECTROPHILLIC ADDITION: A reaction in which a C=C is saturated and in which the initial
reaction is an attack by an electrophile.
CARBOCATION: A positive ion formed by the reaction.
A negatively charged ion forms a bond with the carbocation.

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H is slightly positive, Br is slightly negative.
The bond in the hydrogen bromide breaks heterolytically.
1) Electrophile attracted to the C=C/electron rich bond
2) Electrophile accepts a pair of electrons.
3) The Br takes the pair of electrons ... Br this leaves a carbocation.
4) The neg. Charged ion bonds to the carbocation.
ASYMMETRICAL ALKENES
Alkyl groups have a tendency to release electrons via covalent bond. This is known as a positive
inductive effect.…read more

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SULFURIC ACID
Electrophillic addition
Concentrated HSO
Exothermic
The water is added to release the sulfuric acid by hydrolysis... making the alcohol.
INDUSTRIAL PRODUCTION OF ALCOHOLS:
600K ­ high temperature
6000kPa - high pressure
HPO catalyst (phosphoric acid)
REACTION WITH HYDROGEN
Reagent: H
Catalyst: Nickel
Electrophillic addition also called
HYDROGENATION
ADDITION POLYMERISATION...
Monomer: Alkene/alkene derivative
Polymer: Many alkenes joined, covalent bonding.
Conditions: different catalysts, temperature, pressure forms different polymers/properties
(chains, branching, cross links)
REPEATING UNIT: Smallest group of atoms repeated in the polymer.…read more

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A section of polymer
Identify a repeated unit, find any pair of carbons and circle it.
The monomer is the alkene of the repeating unit.
PROBLEMS WITH PLASTICS:
They are NOT BIODEGRADABLE.
Buried plastics in landfill sites may take hundreds of years to decompose.
Plastic litter can also cause problems for animals that ingest it because it blocks their
intestinal tracts.
SOLUTIONS: Recycle, reduce amount used.
Mechanical recycling:
It separates different types of plastics.
It washes, sorts and grounds plastic into small pellets.…read more

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