Question 1

What is added when bromine reacts with an alkene?

Accepted Answer

Bromine adds across the carbon-carbon double bond, placing one bromine atom on each of the two adjacent alkene carbons. The product is therefore a vicinal dihalide rather than a compound with both bromines on the same carbon.

Question 2

Why are halogen addition products formed in an anti relationship?

Accepted Answer

The alkene forms a three-membered bromonium bridge. Bromide opens this bridge from the opposite face, so the two new carbon-bromine bonds form with anti stereochemistry.

Question 3

What is the Markovnikov orientation of a halohydrin?

Accepted Answer

In halohydrin formation, the hydroxyl group is placed on the more substituted alkene carbon and bromine remains on the less substituted carbon. The OH and Br groups have the anti relationship produced by bridge opening.

Question 4

How do cis-2-butene and trans-2-butene give different stereochemical products?

Accepted Answer

Anti bromination of cis-2-butene gives a racemic pair consisting of (2R,3R) and (2S,3S). Anti bromination of trans-2-butene gives the meso (2R,3S) product.

Question 5

Is hydrogenation an example of halogen addition?

Accepted Answer

No. Hydrogenation is the addition of hydrogen over a double bond using a catalyst such as nickel, platinum, or palladium, and it forms an alkane. Halogen addition instead uses bromine or chlorine and forms a vicinal dihalide.

Bromine or Chlorine Addition Across an Alkene Double Bond

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