Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to produce a mixture of five products, A, B, C, D and E - AQA - A-Level Chemistry - Question 3 - 2022 - Paper 3
Question 3
Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to produce a mixture of five products, A, B, C, D and E.
Products A, B and C are alkenes.
A i... show full transcript
Worked Solution & Example Answer:Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to produce a mixture of five products, A, B, C, D and E - AQA - A-Level Chemistry - Question 3 - 2022 - Paper 3
Step 1
1. Give the names of the two concurrent mechanisms responsible for the formation of the alkenes and the alcohols.
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Answer
Mechanism to form alkenes: Elimination mechanism.
Mechanism to form alcohols: Nucleophilic substitution mechanism.
Step 2
2. Define the term stereoisomers.
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Answer
Stereoisomers are different compounds that have the same molecular formula and structural formula but differ in the spatial arrangement of their atoms.
Step 3
3. Deduce the name of isomer A. Explain why A does not exhibit stereoisomerism.
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Answer
Name: 1-butene.
Explanation: A does not exhibit stereoisomerism because it does not have a double bond, hence cannot have geometric isomers.
Step 4
4. Outline the mechanism for the reaction of 2-bromobutane with sodium hydroxide to form alkene A.
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Answer
The mechanism involves a base-induced elimination, where sodium hydroxide abstracts a proton from 2-bromobutane, leading to the formation of a double bond and the expulsion of bromide ion.
Step 5
5. Deduce the name of isomer B and the name of isomer C. Explain the origin of stereoisomerism in B and C.
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Answer
Names: Isomer B is 2-butene, Isomer C is E-butene.
Explanation: The stereoisomerism arises due to the presence of a double bond that restricts rotation, resulting in cis and trans isomers.
Step 6
6. Draw 3D representations of enantiomers D and E to show how their structures are related.
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Answer
Enantiomers D and E can be represented using wedge and dashed bonds to illustrate their three-dimensional arrangement around the chiral center.
Step 7
7. State and explain the order in which precipitates appear.
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Answer
Order in which precipitates appear: 1-iodobutane > 1-bromobutane > 1-chlorobutane.
Explanation: The rate of hydrolysis is faster for iodo compounds due to the weaker C-I bond compared to the C-Br and C-Cl bonds, leading to quicker precipitation.
