Question

25 multiple choice 2 points
addition of br₂ to (e)-hex-3-ene produces _.
(z)-3,4-dibromo-3-hexene
a meso dibromide
a mixture of enantiomeric dibromides which is optically active
a mixture of enantiomeric dibromides which is optically inactive

Explanation:

Step1: Analyze the reaction mechanism

The addition of \(Br_2\) to an alkene occurs via anti - addition. For \((E)\) - hex - 3 - ene (\(CH_3CH_2CH = CHCH_2CH_3\)), when \(Br_2\) adds across the double bond.

Step2: Consider symmetry and chirality

The product has a plane of symmetry. A meso compound is a compound that contains chiral centers but is achiral overall due to the presence of a plane of symmetry. In the case of the addition of \(Br_2\) to \((E)\) - hex - 3 - ene, the product \(3,4 -\) dibromohexane has a plane of symmetry (passing through the mid - point of the \(C3 - C4\) bond). So it is a meso dibromide.

• Option A: \((Z)\) - 3,4 - dibromo - 3 - hexene is incorrect because the reaction is an addition to an alkene (not forming another alkene with a \(Z\) configuration in this context, the reaction is \(Br_2\) addition across \(C = C\) to form a dibromide).
• Option C and D: Since it is a meso compound (not a racemic mixture of enantiomers), these options are wrong. A racemic mixture (a mixture of enantiomers) would be formed if the starting alkene was not symmetric. But \((E)\) - hex - 3 - ene is symmetric about the \(C3 - C4\) double bond, and the anti - addition of \(Br_2\) gives a meso compound.

Answer:

B. a meso dibromide