AQA A Level Chemistry: Year 1- Alkenes Already Passed

AQA A Level Chemistry: Year 1- Alkenes Already Passed What is an alkene? An unsaturated hydrocarbon What is an unsaturated hydrocarbon? A compound containing only carbon and hydrogen atoms and containing at least one carbon carbon double bond What are van der Waals forces? Relatively weak intermolecular forces caused by temporary dipole dipole interaction What is the general formula for an alkene? CnH2n How would you name an alkene given its displayed formula? Identify the longest carbon chain Identify the position of the carbon carbon double bond Identify any side chains What are structural isomers? Molecules with the same molecular formula, but with different a structural formula What are stereoisomers? Molecules with the same molecular AND structural formula but a different 3D arrangement of their atoms in space What is E-Z isomerism? The highest priority groups are on the same side of the double bond Describe the C=C double bond Double covalent bond Planar bond Area of high electron density How do you assign the highest priority of groups in E-Z isomerism? The highest atomic number closest to the double bond has the highest priority If two groups have e.g. Only carbon and hydrogen, then the one with the most carbon atoms is assigned the highest priority What are Z isomers? Molecules where the highest priority groups are on the same side What are E isomers? Molecules where the highest priority groups are on opposite sides What is addition polymerisation? The reaction by which alkenes (or substituted alkenes) react with other alkene (or substituted alkene) molecules to form polymers What polymer would the monomer ethene form? Poly(ethene) What is a polymer? A long chain of repeating monomer units joined together Why are addition polymers unreactive? They lack the reactive carbon-carbon double bond Which is an area of high electron density And so vulnerable to electrophilic attack What is PVC? Poly(chloroethene) What is PVC used for? PVC: Wellies, raincoats, uPVC: Drainpipes, window/door frames Electrical wire insulation Describe PVC A rigid plastic What is the difference between uPVC and PVC? A plasticiser molecule has been added to PVC to make it more flexible for its use in clothing What are the forces between polymer molecules? Weak van der Waals' forces Why do some polymers melt over a range of temperatures? Consist of chains of different lengths varying strength of van der Waals' When will a polymer melt? When the (intermolecular) van der Waals forces are overcome Why are the intermolecular forces between polymers often strong? Chains are often long Many electrons Many van der Waals' Explain why a tertiary carbocation forms the major product and a secondary/primary carbocation forms the minor product Tertiary carbocation has more alkyl groups attached Positive inductive effect Reduce + charge on carbon More stable Remains in reaction mixture for longer so more likely to react with electrophile Give a physical properties of polymers They have high melting/boiling points When asked to draw the repeating unit what should you draw? Just the atoms and bonds (single covalent) There should be no brackets or n Why are polymers with very few branches strong and hard? Very compact Chains can pack together van der Waals' strong Why are branched polymers weaker and softer? The polymer chains cannot pack closely together van der Waals' between chains weaker What is an electrophile? A substance which can accept a pair of electrons (electron pair acceptor) What is a carbocation? A species which contains a positive charge on a carbon atom Describe the mechanism by which HBr is added to ethene e-'s move from area of high electron density to delta + H e-'s in H-Br bond move to delta - Br Carbocation forms Lone pair of e-'s on :Br- attracted to C+ HBr has been added across the double bond What key phrase is used to describe how the C=C bond is broken by electrophiles? Electrophile has been added across the double bond What is the product of the addition of H2SO4 to an alkene called? alkylhydrogensulfate How is Br2 reacted with alkenes? Br2 gas bubbles through alkene Absence of light Temperatures below room temp Describe the test for unsaturation Bromine added to water to form bromine water Bromine water mixed with organic sample If colour changes from orange to colourless (without gas released) there are C=C bonds present If remains orange, there are no C=C bonds Knowledge and understanding of the production and properties of polymers has developed over time Knowledge and understanding of the production and properties of polymers has developed over time Put the carbocations in order of stability primary secondary tertiary Explain when major and minor products form in electrophilic addition to unsymmetrical alkenes Major product formed via carbocation which has most alkyl groups bonded to it Minor product is formed via carbocation which has least alkyl groups bonded to it Tertiary carbocation more stable than secondary more stable that primary How does the electrophile form in non-polar molecules such as Br2? When molecule moves close area of high electron density (C=C double bond) It becomes polarised Electrons in C=C repel electrons in neutral molecule Forms polar electrophile True or False The electrophilic addition reactions of HBr or conc H2SO4 and alkenes occur below room temperature True And at a good rate for HBr! True or False Dilute sulphuric acid is an electrophile False Concentrated sulphuric acid is an electrophile Why are alkenes vulnerable to electrophilic attack? Contain C=C double bond Area of high electron density If the monomer is 2-chloropropene, what is the polymer? poly(2-chloropropene) What is an addition reaction? A reaction in which two molecules join together to make one larger molecule What is heterolytic fission? Covalent bond breaks and both electrons move to one atom. Two oppositely charged ions are formed