Which reaction is the best method to synthesize a vicinal dibromide from an alkene?

• A. Ozonolysis of the alkene followed by reduction
• B. Hydrogenation of the alkene using $H_2$ and a palladium catalyst
• C. Addition of ${\mathrm{Br}}_2$ to the alkene in an inert solvent
• D. Reaction of the alkene with aqueous ${\mathrm{HBr}}_{\mathrm{}}$

Answer: (C)

Verified step by step guidance

1. Identify the goal: synthesizing a vicinal dibromide means adding two bromine atoms to adjacent carbons of the alkene double bond.
2. Recall that ozonolysis cleaves the double bond to form carbonyl compounds, so it does not add bromines across the double bond and is not suitable for vicinal dibromide synthesis.
3. Hydrogenation with H\_2 and a palladium catalyst adds hydrogens across the double bond, saturating it, but does not introduce bromine atoms.
4. Reaction with aqueous HBr adds a bromine and a hydrogen across the double bond (hydrohalogenation), resulting in a bromoalkane but not a vicinal dibromide.
5. Addition of Br\_2 to the alkene in an inert solvent proceeds via a bromonium ion intermediate, leading to anti addition of two bromine atoms on adjacent carbons, which is the best method to synthesize a vicinal dibromide.