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Question 1
This question is about the structure and properties of alkenes. Alkenes are unsaturated hydrocarbons. |
a) | Explain the meaning of the term unsaturated.
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b) | Give the general formula of an alkene.
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c) | What is the geometric shape around the carbon atoms involved in the double bond of an alkene?
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d) | Explain the term pi-bond in relation to the carbon-carbon double bond of an alkene.
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e) | Why are alkenes generally more reactive than alkanes?
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Question 2
This question is about the addition reactions of 2-methylpropene. 2-methylpropene can undergo an addition reaction to form 2-methylpropane. |
a) | Suggest suitable reagents and conditions for this reaction.
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b) | Name the type of product formed when 2-methylpropene reacts with steam in the presence of an acid catalyst.
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c) | Name and outline a mechanism for the reaction between 2-methylpropene and hydrogen bromide to form 2-bromo-2-methylpropane.
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d) | Draw the structure of the alternative carbocation that could be formed in the reaction between 2-methylpropene and hydrogen bromide.
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e) | Explain why the carbocation you drew in part d) leads to the formation of a minor product.
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Question 3
Alkenes undergo addition reactions to form saturated compounds. |
a) | Define the term electrophile.
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b) | Complete the mechanism below for the reaction between ethene and HCl.
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c) | When 2-methylbut-2-ene reacts with HCl, two products are formed as shown in the diagram below. Explain which of the two structures shown will be the major product.
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d) | Describe the test for an unsaturated hydrocarbon. Include the positive result of the test in your answer.
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Question 4
The alkene hex-3-ene has stereoisomers. |
a) | Explain the meaning of the term stereoisomer.
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b) | Draw the structures of the E and Z isomers of hex-3-ene.
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c) | The alkene 3-methylpent-2-ene is an isomer of hex-3-ene. Outline a mechanism for the reaction of 3-methylpent-2-ene with HBr to form 3-bromo-3-methylpentane.
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d) | Explain why 3-bromo-3-methylpentane is the major product in this reaction.
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Question 5
The diagram below shows the structure of an alkene, X. |
a) | Explain why alkene X does not have E/Z stereoisomers.
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b) | Alkene Y is a structural isomer of alkene X which does show E/Z stereoisomerism. Draw the structure of the Z-isomer of alkene Y, and name this isomer.
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c) | Alkene Y is reacted with steam in the presence of an acid catalyst. Draw the structure of the product formed.
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Question 6
This question is about the alkene but-1-ene. |
a) | Explain why the bond angle of the carbon atoms in the double bond of but-1-ene are approximately 120°.
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b) | Why does but-1-ene react more readily than butane?
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c) | Draw the mechanism for the reaction between but-1-ene and Br2 to form 1,2-dibromobutane.
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d) | Explain why the reaction of but-1-ene with HCl results in the formation of two isomeric products.
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e) | Draw the structure of the product formed when but-1-ene is reacted with cold, acidified KMnO4.
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Question 7
This question is about unsaturated hydrocarbons. |
a) | Define the term unsaturated.
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b) | Three reactions of propene are shown below. Complete the flowchart to show the structures of the products formed.
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c) | The alkene pent-2-ene exists as stereoisomers. Explain the meaning of the term stereoisomers.
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d) | Draw the structure of the E-isomer of pent-2-ene.
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