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22 Cards in this Set
- Front
- Back
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Explain the double bond present in Alkenes |
The double bond consists of a sigma and a pi bond. 3/4 of the electrons are involved in the sigma bonds and the one electron each from each carbon atoms are in the pi orbital and are in the pi bond. The pi bond is the sideways overlap of the p orbitals which are situated above and below the plane of the double bond Because the pi bonds electron density is concentrated above and below the double bond it locks the two carbons in position and prevents rotation Shape of carbon atom in Allene is trigonal planar |
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What does electron density mean? |
Probability of finding an electron in a specific location around an atom or molecule |
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What are stereoisomers? |
Compounds with the same structural formula but with a different arrangement of atoms in space |
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What are the two types of stereoisomers and explain the differences between them? |
E/Z isomers- isomers that contain a carbon double bond and the groups around each carbon atom are different Optical isomers can occur in a wide range of compounds |
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Why does stereoisomers occur? |
The pi bond restrict movement around the double bond so the groups are held in a fixed position. |
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What is cis trans isomerism? |
Special case of E/Z isomerism except that one of the groups on each carbon atom must be hydrogen Cis- hydrogens on the same size of molecule (Z) Trans- hydrogens locates diagonally opposite each other (E) |
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Explain the Cahn ingold prelog rules |
•if the highest priority groups are placed on the same side of the double bond, the compound is a Z isomer •if the highest priority groups are placed diagonally opposite each other, the compound is an E isomer |
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Why are alkenes more reactive than Alkanes? |
The pi bond is situated above and below the plane of the bond so the electron density is outside the double bond so the electrons in the pi bond are exposed so the pi bond can be broken easily and undergo reactions |
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What are the four types of addition reactions that alkenes go through? |
•alkenes and hydrogen Halides (room temp) if alkene is a gas, both reactants are mixed together. If alkene is a liquid, halogen halide is bubbles through •alkenes and halogens (room temp) •alkenes and steam (phosphoric acid catalyst) •alkenes and hydrogen (nickel catalyst, 423K) |
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What is the method for testing for unsaturation? |
1) bromine (orange) is added dropwise to sample of alkene 2) bromine breaks double bond (of it is present) 3)orange to colourless |
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What is electropholic addition? |
A mechanism for addition reactions which alkenes are usually involved in The pi bond is a region of high electron density which attracts electrophiles Electrophiles are atoms or molecules which are attracted to an electron rich centre and are usually a positive ion or molecule |
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Explain the mechanism between ethene and hydrogen bromide |
•bromine is more electronegative than hydrogen so the molecule is polar •pair of electrons in double bond is attracted to the positive hydrogen so bond forms here •hydrogen bromide molecule breaks by heterolytic fission •carbocation is formed •bromine reacts with carbocation |
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Explain the mechanism between ethene and bromine molecule |
•bromine is a non polar molecule •as it approaches the alkene the interaction between the pi electrons and the electrons in the br2 molecule causes polarisation of the br2 molecule indicting a dipole •the electron pair in the pi bond is attracted to the positive be so the double bond is broken •br br bond is broken by heterolytic fission •carbocation is formed •carbocation and br- reacts together |
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Describe and explain markownikoffs rule |
-applies to unsymmetrical alkenes -applies to halogen halide reactions -states that the hydrogen of the hydrogen Halide attaches to the carbon with the most hydrogen atoms and the fewest carbon atoms The halogen attaches itself to the most stable carbocation which is determined by the number of alkyl groups as alkyl groups push and donate their electrons towards the positive charge on the carbocation so the charge is more spread out and more stable |
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Primary secondary tertiary carbocations |
Primary- one alkyl group attached Secondary- two alkyl groups attached Tertiary- three alkyl groups |
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What are the 5 polymers commonly used? |
Poly ethene: supermarket bags and toys Polychloroethene/ poly vinyl chloride: pipes Polypropene- children’s toys and packaging crates Polystyrene/phenyl ethene: used for packagin food as it has thermal insulating properties Tetra Fluor ethene- coating for non stick pans |
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What are the 5 polymers commonly used? |
Poly ethene: supermarket bags and toys Polychloroethene/ poly vinyl chloride: pipes Polypropene- children’s toys and packaging crates Polystyrene/phenyl ethene: used for packagin food as it has thermal insulating properties Tetra Fluor ethene- coating for non stick pans |
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What are three advantages of polymers? |
•readily Available •cheap •not reactive so can be used to store food |
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What are the 5 polymers commonly used? |
Poly ethene: supermarket bags and toys Polychloroethene/ poly vinyl chloride: pipes Polypropene- children’s toys and packaging crates Polystyrene/phenyl ethene: used for packagin food as it has thermal insulating properties Tetra Fluor ethene- coating for non stick pans |
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What are three advantages of polymers? |
•readily Available •cheap •not reactive so can be used to store food |
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What’s a disadvantage of polymers? |
Non biodegradable |
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What are the 6 ways of disposing of waste polymers? |
Recycling- conserves fossil fuels and less waste goes in landfills. Has to be sorted out by type which can be time consuming and expensive PVC recycling- pvc has a high chlorine content and burns into hydrogen chloride gas which is corrosive. Advantage is that new technology uses solvent to dissolve polymer which is precipitated and the solvent is used again Fuel- advantages- makes electricity Requires incineration Feedstock recycling- uses thermal processes to separate monomers, similar way to fractional distillation. Uses fossil fuels. Doesn’t have to be sorted by type. Biodegradable polymers- less waste in landfills, no toxic residue Photodegradable- bonds are weakened by absorbing light |
