Alkenes
- Created by: Chloe Trotter
- Created on: 21-04-16 09:19
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- Alkenes
- Stereoisomerism
- Have the same structural formula but different arrangement of atoms
- EZ Isomers
- Two different groups attached to either end
- Can't rotate because of the double bond
- Alkanes can rotate because of single bond
- E - priority groups at opposite sides
- Z - Priority groups at the same side
- Priority group is atoms with bigger Ar
- Electrophilic addition reactions
- Reaction of hydrogen bromide with Alkene
- Works the same with hydrogen chloride
- Bromine is more electronegative than hydrogen
- Makes the molecule polar
- H delta+ is attracted to the electron rich pi bond
- Lead to a major and a minor product when the alkene is unsymmetrical
- Markownikoff's rule
- Bromine added to the carbon with the fewest hydrogens attached to it
- Both products are haloalkanes
- Major product formed by the more stable carbocation
- More stable carbocation = electrons from methyl groups reduce the ions charge
- Markownikoff's rule
- Lead to a major and a minor product when the alkene is unsymmetrical
- At room temperature
- Reaction of sulphuric acid with alkenes
- Two stages
- Electrophilic addition and then hydrolysis
- Electrophilic addition produces alkyl hydrosulphate
- Hydrolysis makes alcohol
- Add water to split molecules
- Electrophilic addition and then hydrolysis
- Room temperature
- Sulphuric acid can be drawn in two different ways
- H2SO4 in equations
- H-OSO2OH in the mechanism
- Role of sulphuric acid is a catalyst as it is regenerated
- Can have major and minor products
- Two stages
- Reaction of bromine with alkenes
- At room temperature
- The electron pair in the Br-Br bond is repelled inducing a dipole
- Becomes polar and electrophilic
- Electron from C=C transfers to Br
- C has a positive charge after
- Carbocation
- :Br- attracted to C+
- Product is a dihaloalkane
- :Br- attracted to C+
- Carbocation
- Makes :Br-
- :Br- attracted to C+
- Product is a dihaloalkane
- :Br- attracted to C+
- C has a positive charge after
- Double bonds in alkenes have areas of high electron density
- Attracts electrophiles
- Addition reaction: two molecules become one product
- Reaction of hydrogen bromide with Alkene
- Industrial hydration
- Alkenes are converted to alcohols in one step rather than two
- Uses water in the presence of an acid catalyst
- Process is called hydration
- Needs high pressures so can't be done in a labratory
- Has a high atom economy so it is cheaper to carry out overall
- Uses water in the presence of an acid catalyst
- Alkenes are converted to alcohols in one step rather than two
- Testing for Alkenes
- Bromine de-colourises in the presence of a double bond
- Brown to clear/transparent
- Bromine de-colourises in the presence of a double bond
- Addition Polymers
- Poly(alkenes) are unreactive
- Because of strong C-C, C-H bonds
- Repeated unit doesn't have a double bond
- Poly(ethene)
- Used to make plastic bags/buckets/bottles
- Flexible, easily moulded, waterproof, chemical proof and low dencity plastic
- Poly(Propane)
- Stiffer polymer used in utensils and containers and the fibres in robe and carpets
- Formed from alkenes in a process called addition polymerisation
- Poly(alkenes) are unreactive
- Unsaturated hydrocarbons
- General formula CnH2n
- C=C
- Numbers are added to the names to show the position of the double bond
- Stereoisomerism
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