In the given reaction, an alcohol reacts with HBr to form a carbocation intermediate. Let's analyze the steps involved and determine the number of hyperconjugation structures that stabilize this carbocation.
Step 1: Carbocation Formation When the alcohol reacts with HBr, the -OH group is protonated and leaves as water, forming a carbocation at the carbon previously bearing the -OH group.
Step 2: Identify the Carbocation The resulting carbocation is tertiary and located at the carbon attached to the methyl group.
Step 3: Hyperconjugation Stabilization Hyperconjugation involves the overlap of the filled σ-orbitals of C-H bonds with the empty p-orbital of the carbocation. Each adjacent C-H bond can contribute a hyperconjugation structure.
Step 4: Counting Hyperconjugation Structures The carbocation is adjacent to the following C-H bonds:
3 C-H bonds from the adjacent methyl group.
3 C-H bonds from the three other equivalent hydrogens (considering possible rotations).
This totals 6 hyperconjugative structures.
However, if the reaction conditions allow for rotation, an additional hyperconjugation structure may be considered from the adjacent ring hydrogen, making it 7.
Conclusion: The number of hyperconjugation structures stabilizing the carbocation is 7, which is confirmed to lie within the given range (7,7).
