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Question #44432
The Question
Compound is 1-(trimethylsiloxy)cyclopentene. It is subjected to the following reaction sequence:
- 9-BBN (9-borabicyclo[3.3.1]nonane), THF
- , (aq)
- Dilute
The resulting major organic product is isolated and then treated with:
- (aq), 298 K
to yield compound . Identify compound .
Options
- A.
trans-1,2-cyclopentanediol
- B.
Pentanedial
- C.
cis-1,2-cyclopentanediol
- D.
Cyclopentanone
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Mechanism_Trap
Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.
Concepts Behind This Question
Glycol Periodic Acid Cleavage|Hydroboration-Oxidation Regiochemistry
Why This Question Is Tricky
Common Mistakes
This problem tests the stereochemical constraints of two distinct reactions.
First, students must deduce that syn-hydroboration of a silyl enol ether yields a trans-1,2-diol after oxidation and deprotection, because the syn addition of H and B forces the existing -OTMS group and the incoming B atom into a trans relationship.
The critical trap lies in the final step: students commonly assume that all vicinal diols undergo oxidative cleavage with periodic acid ().
However, the Criegee mechanism requires the formation of a cyclic periodate ester.
While trans-1,2-cyclohexanediol can slowly cleave via a diequatorial conformation, trans-1,2-cyclopentanediol is too rigid to form the highly strained trans-fused 5,5-bicyclic intermediate.
Thus, the reaction fails, trapping students who ignore the geometric requirements of the intermediate.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Alcohols, Phenols, and Ethers - Class 12 |
| Concept | Glycol Periodic Acid Cleavage |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |