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Which compound reacts with hydrogen bromide to give 2-bromo-3-methylbutane as the major product? A (CH₃)₂C=CH₂ B CH₃(CH₂)2CH=CH₂ - AQA - A-Level Chemistry - Question 28 - 2020 - Paper 3
Question 28
Which compound reacts with hydrogen bromide to give 2-bromo-3-methylbutane as the major product? A (CH₃)₂C=CH₂ B CH₃(CH₂)2CH=CH₂. C CH₃CH₂C(CH₃)=CH₂ D (CH₃)₃CCH=CH₂
Worked Solution & Example Answer:Which compound reacts with hydrogen bromide to give 2-bromo-3-methylbutane as the major product? A (CH₃)₂C=CH₂ B CH₃(CH₂)2CH=CH₂ - AQA - A-Level Chemistry - Question 28 - 2020 - Paper 3
Step 1
Identify the major product
Answer
In this reaction, hydrogen bromide (HBr) adds to the double bond of an alkene. The product is 2-bromo-3-methylbutane, which suggests that the reaction involves a compound with the potential to rearrange or provide a stable carbocation.
The addition of HBr is a Markovnikov addition, where the bromine atom will attach to the more substituted carbon atom of the double bond.
Step 2
Analyze the options provided
Answer
Now, let's examine each compound:
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A (CH₃)₂C=CH₂: This option will lead to a reaction that forms a secondary carbocation, resulting in potential for rearrangement to form 2-bromo-3-methylbutane.
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B CH₃(CH₂)₂CH=CH₂: This compound is less likely to produce the desired product due to the formation of a less stable carbocation.
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C CH₃CH₂C(CH₃)=CH₂: Although this one has branching, it would not produce 2-bromo-3-methylbutane.
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D (CH₃)₃CCH=CH₂: This structure provides a stable tertiary carbocation upon reaction with HBr, which does not yield the target product either.
From this analysis, option A stands out as the compound that will yield the desired major product.
Step 3