Question

When (±)-2,3-dibromobutane reacts with $KOH$, trans-2-bromobut-2-ene is formed. Which of the following is/are true?

• A. The reaction proceeds via E₂
• B. The reaction proceeds via E₁
• C. Both enantiomers give the same product
• D. This elimination is also known as $\beta$ elimination

Answer 1

Answer: (A), (C), (D)

The correct options are
A

The reaction proceeds via E₂

C

Both enantiomers give the same product

D

This elimination is also known as $\beta$ elimination

For E₂, we need carbon-hydrogen and the carbon-bromine bonds to be anti-periplanar.
They should be coplanar but the $C-Br$ and $C-H$ bonds should be on opposite sides.

After rotation, the antiperiplanar structure is in place for E₁:

For the other enantiomer from the racemic mixture, E₂ looks like: