- A

- B

- C

- D

View written solutionFree
Correct answer: A
- Identify the substrate
The given alcohol is
This is a secondary alcohol. In presence of concentrated , dehydration occurs, generally by an mechanism.
- Write the carbon skeleton around the OH-bearing carbon
Let us label the chain:
The carbon bearing is adjacent to:
- on the left:
- on the right:
After protonation of and loss of water, a carbocation forms at the -bearing carbon:
C_6H_5CH_2-oxed{CH^+}-CH(CH_3)_2- Consider possible rearrangement
This carbocation is secondary. A more stable carbocation can form by hydride shift from the benzylic carbon () to the cationic center.
That gives a benzylic carbocation:
C_6H_5-oxed{CH^+}-CH_2-CH(CH_3)_2This benzylic carbocation is highly stabilized by resonance with the benzene ring, so this rearrangement is favored.
- Elimination from the rearranged carbocation
Now elimination can occur from the adjacent carbon (), giving the alkene:
This alkene is conjugated with the benzene ring through the benzylic double bond, making it especially stable.
- Check other possible alkene(s)
Without rearrangement, dehydration could also give alkenes such as:
Among these, the alkene
is more stable because the double bond is directly conjugated with the phenyl ring. Hence it is the main product.
- Conclusion
The major product is:
So the correct option is A.
- Comparison with stored answer
Stored correct answer: A
Our derived answer: A
Hence, they agree.
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