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Question #44475
The Question
An organic compound (1,2-dibromopropane, ) is treated with exactly of sodium amide () in liquid ammonia at . The reaction is allowed to proceed until no further chemical change occurs, after which the reaction mixture is quenched with excess water. Given that the rate of the first dehydrohalogenation step is significantly greater than the second (), and the acid-base reaction is instantaneous, determine the final organic product composition.
Options
- A.
of propyne
- B.
of propyne and of bromopropenes
- C.
of propyne and of 1,2-dibromopropane
- D.
of bromopropenes
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
Alkynes Terminal Acidity|E2 Regioselectivity (Saytzeff vs Hoffmann)|Alkene Addition Regioselectivity
Why This Question Is Tricky
Common Mistakes
The question tests the 'Limiting Reagent' trap combined with 'Terminal Alkyne Acidity'.
Students often assume that 2 equivalents of a strong base are sufficient to convert a vicinal dihalide to an alkyne.
However, they overlook the hidden variable: the terminal alkyne is a stronger acid than ammonia, so it quantitatively consumes an additional equivalent of the base () to form an acetylide salt.
This acid-base reaction is diffusion-controlled and outcompetes the slower second E2 elimination, effectively altering the reaction stoichiometry to require 3 equivalents for complete conversion.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Hydrocarbons - Class 11 Part 2 |
| Concept | Alkynes Terminal Acidity |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |