Question

Identify alkene give meso product on reaction with $Br_2$ / $CCl_4$?

• A. P
• B. Q
• C. R
• D. S

Answer 1

Answer: (C)

R

Answer 2

Addition of $Br_2$ to alkenes is an anti-addition.

• Addition of $Br_2$ to 2-methylpropene gives 1,2-dibromo-2-methylpropane, which is achiral.
• Addition of $Br_2$ to cis-but-2-ene gives a racemic mixture of (2R,3R)- and (2S,3S)-2,3-dibromobutane.
• Addition of $Br_2$ to trans-but-2-ene gives meso-2,3-dibromobutane.
• Addition of $Br_2$ to but-1-ene gives a racemic mixture of (R)- and (S)-1,2-dibromobutane.

The alkene that gives a meso product is trans-but-2-ene, which is R.