Number of Stereoisomers from Bromination of trans-2-Butene

Electrophilic addition of bromine ($\text{Br}_2$) across an alkene proceeds via a cyclic bromonium ion intermediate, resulting in stereospecific anti-addition.

• Anti-addition of $\text{Br}_2$ to a trans-alkene yields a symmetric meso compound:
  $\textit{trans}\text{-2-butene} + \text{Br}_2 \xrightarrow{\text{anti-addition}} \textit{meso}\text{-2,3-dibromobutane}$

• The meso form possesses an internal plane of symmetry (and center of inversion in staggered conformation), making it achiral and superimposable on its mirror image.

• Therefore, only 1 stereoisomer is obtained.

Correct Answer: A