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Question #45092
The Question
Consider the elimination reactions of 3-bromo-2,2-dimethylbutane under two different sets of conditions at :
Reaction I: Solvolysis in pure \ce{C2H5OH} yields alkene as the major product. Reaction II: Treatment with \ce{C2H5ONa} in anhydrous dimethyl sulfoxide (DMSO) yields alkene as the major product.
Let and be the number of hyperconjugative -hydrogens present in the major products and , respectively. Calculate the value of .
Options
- A.
120
- B.
12
- C.
132
- D.
0
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Exception_Exposure
Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.
Concepts Behind This Question
Bond Cleavage Energetics|Electrophile vs Nucleophile|E1/E2 Solvent and Base Effects
Why This Question Is Tricky
Common Mistakes
The problem tests the 'Effective Bond Cleavage Energetics' dictated by solvent effects, a common trap for students who rely solely on the substrate's electronic profile.
While the substrate can form a stable rearranged carbocation, aprotic solvents (DMSO) fail to solvate the leaving group, creating a high kinetic barrier for heterolysis.
Coupled with a strong, unsolvated base (EtO-), the mechanism is forced into a concerted E2 pathway.
Furthermore, the steric blockade at the quaternary beta-carbon forces absolute regioselectivity in the E2 pathway, contrasting sharply with the rearranged Zaitsev product of the E1 pathway.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2 |
| Concept | Bond Cleavage Energetics |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |