Draw all possible products that will form from this reaction, and draw the electron-pushing mechanism for one of the elimination products that you form. Indicate which of the elimination products are favored. Br
The Correct Answer and Explanation is:
To fully answer your question, I need a bit more context about the specific reactants and reaction conditions. However, based on your reference to “Br” and elimination products, I will assume the reaction involves 2-bromobutane undergoing E1 or E2 elimination, typically with a strong base like NaOEt or heat in alcohol. I’ll provide the possible products, a mechanism for one, and explain which is favored.
Reaction Overview
Reactant: 2-bromobutane
Base: Strong base (e.g. NaOEt or KOH)
Reaction type: Elimination (E2 or E1)
Possible Elimination Products
From 2-bromobutane, the elimination can lead to two alkene isomers:
- But-2-ene (more substituted alkene)
- Exists as cis and trans isomers
- But-1-ene (less substituted alkene)
These result from the removal of a β-hydrogen adjacent to the carbon bearing the bromine atom.
Electron-Pushing Mechanism (E2 Example with Base: EtO⁻)
Mechanism for the formation of trans-but-2-ene:
- The strong base (EtO⁻) abstracts a β-hydrogen from the carbon adjacent to the carbon bonded to Br (specifically from C-3 in this case).
- As the base pulls off the proton, the electrons from the C-H bond form a π bond between C-2 and C-3.
- The leaving group (Br⁻) leaves at the same time.
- This is a concerted, one-step E2 mechanism.
Product Favorability
According to Zaitsev’s Rule, the more substituted alkene is favored in elimination reactions. Therefore:
- Trans-but-2-ene is the major product because it is the most stable due to both alkene substitution and steric stability.
- Cis-but-2-ene is a minor product due to steric strain.
- But-1-ene is the least favored as it is less substituted.
Conclusion (Summary)
In this elimination reaction of 2-bromobutane with a strong base, three products form: trans-but-2-ene, cis-but-2-ene, and but-1-ene. The trans isomer of but-2-ene is favored due to greater thermodynamic stability. The reaction proceeds via the E2 mechanism when a strong base is used, and the elimination follows Zaitsev’s Rule, favoring the more substituted double bond.
