Before You Begin
Question #44345
The Question
Consider the reaction of 3-fluoro-2-butanone with Lithium diisopropylamide (LDA, 1.05 eq) in THF at , followed by quenching with trimethylsilyl chloride (TMSCl). What is the major organic product formed?
Options
- A.
2-fluoro-3-(trimethylsilyloxy)-2-butene
- B.
3-fluoro-2-(trimethylsilyloxy)-1-butene
- C.
1-fluoro-2-(trimethylsilyloxy)-2-butene
- D.
2-(trimethylsilyloxy)-1,3-butadiene
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
Bent's Rule|Enolate Regioselectivity|Hybridization in Non-Standard Cases
Why This Question Is Tricky
Common Mistakes
This question tests a critical exception to the standard 'kinetic vs. thermodynamic enolate' paradigm.
Students are taught that bulky bases like LDA at low temperatures strictly follow steric control, yielding the less substituted enolate.
The hidden variable here is Bent's Rule: the highly electronegative alpha-halogen alters the orbital hybridization of the alpha-carbon.
By pulling p-character into the C-X bond, it forces higher s-character into the C-H bond, drastically increasing its kinetic acidity.
This electronic acidification overrides steric hindrance, causing the kinetic enolate to form at the more substituted, halogenated position.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Chemical Bonding and Molecular Structure - Class 11 Part 1 |
| Concept | Bent's Rule |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |