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| Question | Answer |
| Why are alkenes able to undergo electrophilic addition reactions? | The double bond has got plenty of electrons and is easily attacked by electrophiles. The double bond is also nucleophilic |
| What are electrophiles? | Electron pair acceptors (e.g. H⁺ and NO₂⁺) |
| What are nucleophiles? | Electron pair donors |
| What is the general electrophilic addition reaction equation for ethene and XY? | H₂C=CH₂ + X-Y --> CH₂XCH₂Y |
| Describe the mechanism for electrophilic addition | 1. The X-Y bond breaks (heterolytic fission) and the electrons are taken from the bond are taken by the Y atom to form a negative ion with a lone pair of electrons 2. Two electrons from the C=C double bond attack the δ+ X atom, creating a new bond between carbon 1 and X 3. Carbon 2 is left electron deficient - it becomes a positively charged carbocation intermediate 4. The Y⁻ acts as a nucleophile, attacking the positively charged carbocation intermediate, donating its lone pair of electrons to form a new bond 5. Overall the X-Y molecule has been added to form a saturated compound |
| Draw the mechanism for electrophilic substitution |
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| Describe the reactants and conditions for the production of alkanes from alkenes | Hydrogen gas Nickel catalyst 150°C |
| Describe the process in which alkenes react to from dihaloalkanes | Alkenes react with halogens to for dihaloalkanes. The halogens add across the double bond, and each of the carbon atoms ends up bonded to one halogen atom. This is an electrophilic addition reaction |
| Give the balanced symbol equation for the reaction between ethene and halogen X₂ | H₂C=CH₂ + X₂ --> CH₂XCH₂X |
| Describe the test for unsaturation | Add bromine water to your unknown hydrocarbon sample If your unknown hydrocarbon is an alkene, the colour will change from orange to colourless (dibromoalkane, which is colourless, is made) |
| Describe the reactants and conditions for the production of alcohols from alkenes | Hydrated by steam 300°C 60-70atm Solid phosphoric (V) acid catalyst |
| For the production of ethanol from ethene, the reaction is reversible and the reaction yield is low (5%). What can be done to increase the yield? | Recycle the unreacted ethene gas This makes the overall yield of ethene 95% |
| What do alkenes react with to form haloalkanes? What type of reaction is this? | Hydrogen halides Electrophilic addition reaction |
| What does Markownikoff's rule state? | The major product from addition of a hydrogen halide (HX) to an unsymmetrical alkene is the one where hydrogen adds to the carbon with the most hydrogens already attached. The reaction to form this product will have occurred via the most stable carbocation intermediate |
| TRUE OR FALSE: If the hydrogen halide adds to a symmetrical alkene (e.g. ethene), only one product can be formed | TRUE |
| Complete the sentences: If the hydrogen halide adds to an unsymmetrical alkene, there are _____ possible products. The amount of each product formed depends on how _________ the ________________ formed in the middle of the reaction is. | If the hydrogen halide adds to an unsymmetrical alkene, there are TWO possible products. The amount of each product formed depends on how STABLE the CARBOCATION formed in the middle of the reaction is. |
| What are the three possible carbocations? |
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| TRUE OR FALSE: Carbocations with more alkyl (R) groups are more stable | TRUE |
| Carbocations with more alkyl (R) groups are more stable. Why? | The alkyl groups feed electrons towards the positive charge |
| How can you show that an alkyl group is donating electrons in a diagram? | Drawing an arrow on the bond that points to where the electrons are donated |
| TRUE OR FALSE: Less stable carbocations are much more likely to form than more stable ones | FALSE MORE stable carbocations are much more likely to form than LESS stable ones. The first step of the mechanism is more likely to lead to the formation of the most stable carbocation |
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