Photo AI
Which alkene reacts with hydrogen bromide to give 2-bromo-3-methylbutane as the major product? A (CH₃)₂C=CHCH₃ B CH₃CH=CHCH₂ C CH₃CH=C(CH₃)=CH₂ D (CH₃)₂C=CH₂ - AQA - A-Level Chemistry - Question 33 - 2019 - Paper 3
Question 33
Which alkene reacts with hydrogen bromide to give 2-bromo-3-methylbutane as the major product? A (CH₃)₂C=CHCH₃ B CH₃CH=CHCH₂ C CH₃CH=C(CH₃)=CH₂ D (CH₃)₂C=CH₂
Worked Solution & Example Answer:Which alkene reacts with hydrogen bromide to give 2-bromo-3-methylbutane as the major product? A (CH₃)₂C=CHCH₃ B CH₃CH=CHCH₂ C CH₃CH=C(CH₃)=CH₂ D (CH₃)₂C=CH₂ - AQA - A-Level Chemistry - Question 33 - 2019 - Paper 3
Step 1
Identify the Major Product
Answer
The major product stated is 2-bromo-3-methylbutane, which is derived from the addition of hydrogen bromide (HBr) to an alkene. This product indicates that the alkene structure should allow formation of a tertiary carbocation at carbon 3 upon protonation, leading to regioselectivity in the reaction.
Step 2
Analyze Each Alkene Option
Answer
We will analyze each option to determine if it can produce the specified product:
-
Option A: (CH₃)₂C=CHCH₃
- Upon reaction with HBr, the proton adds to the alkene, forming a tertiary carbocation, which can lead to the formation of 2-bromo-3-methylbutane.
-
Option B: CH₃CH=CHCH₂
- This compound would form a secondary carbocation, which is less stable and thus would not lead primarily to the desired product.
-
Option C: CH₃CH=C(CH₃)=CH₂
- This option also leads to a secondary carbocation and will not yield the major product.
-
Option D: (CH₃)₂C=CH₂
- Similar to Option A, this alkene provides the tertiary carbocation upon addition of HBr, allowing for the formation of 2-bromo-3-methylbutane.
Step 3