1,2-Dimethylcyclohexene undergoes only trans-addition with HBr in non-polar solvents but both cis-and trans-additions occur with aq. Acid. Explain.

1,2-Dimethylcyclohexene undergoes only trans-addition with HBr in non-

1.	1,2-Dimethylcyclohexene undergoes only trans-addition with HBr in non-polar solvents but both cis-and trans-additions occur with aq. Acid. Explain.
Answer» Solution :This sterospecific reaction proceeds through a bridged cation like the bromonium ion where `H` replaces `Br`. The intermediate may actually be a `pi` -complex. In the absence of a solvent that can satbilise a FREE `R^(oplus), Br^(Ө)` attacks the protonated complex from the opposite side resulting in trans (anti) addition. In the case of a POLAR solvent such as `H_2 O`,the protonated complex collapses to the free `R^(oplus)`, which now REACTS from both sides (faces) and gives both `CIS-` and trans-additions. .