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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
Step 2
Step 3
Deduce the name of isomer A. Explain why A does not exhibit stereoisomerism.
Answer
Name: But-2-ene (or 2-butene depending on context)
Explanation: A does not exhibit stereoisomerism because it does not have a C=C double bond capable of existing in cis/trans forms due to the lack of different substituents on the double-bonded carbons.
Step 4
Outline the mechanism for the reaction of 2-bromobutane with sodium hydroxide to form alkene A.
Answer
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The hydroxide ion acts as a base and removes a proton from a hydrogen atom adjacent to the bromine-bearing carbon (deprotonation).
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This results in the formation of a double bond between the carbon atoms, while the bromide ion is expelled as a leaving group.
Step 5
Deduce the name of isomer B and the name of isomer C. Explain the origin of stereoisomerism in B and C.
Answer
Names: B is cis-2-butene, C is trans-2-butene.
Explanation: The origin of stereoisomerism in B and C arises from the restricted rotation around the C=C double bond, which leads to different spatial arrangements of the substituents around the double bond.
Step 6
Step 7
State and explain the order in which precipitates appear.
Answer
Order: 1-iodobutane > 1-bromobutane > 1-chlorobutane.
Explanation: The order of hydrolysis rates is based on the reactivity of the halogen; iodine is the best leaving group, followed by bromine and then chlorine. Therefore, 1-iodobutane hydrolyzes fastest, leading to the quickest formation of the precipitate.