Question

The addition of $B{r}_2$ to Z-2-butene gives:

• A. (R,R)-2,3-dibromo butane only
• B. (S,S)-2,3-dibromo butane only
• C. (R,S)-2,3-dibromo butane only
• D. A mixture of (R R) and (S S)-2,3-dibromo butane (50% 50%)
• E. (R,S)-1,2-dibromo butane

Answer 1

The correct option is D A mixture of (R R) and (S S)-2,3-dibromo butane (50% 50%)

Addition of $B{r}_2$ to $Z-2-Butene$ gives equimolar mixture of $(R,R)$ and $(S,S)-2,3$ dibromo butane takes place.

Here $B{r}_2$ approaches from below the plane of the atom of the double bond because it is the region of high electron density.

Here first the formation of a three-membered ring takes place as an intermediate.