Question

The 1,2‑dibromide is synthesized from an alkene starting material. Draw the alkene starting material. Clearly, show stereochemistry of the alkene.

Answer 1

The alkene starting material for the synthesis of 1,2-dibromide can be represented as CHCH=CHCHCHBrBr, with the stereochemistry indicating cis- or trans- isomerism.

Step-by-step explanation:

The alkene starting material for the synthesis of 1,2-dibromide can be represented as CHCH=CHCHCH→BrBr, where the double bond indicates the presence of an alkene. The stereochemistry of the alkene can be shown using cis-trans isomerism. In this case, if the two bromine atoms are on the same side of the double bond, it is cis-1,2-dibromide, and if the two bromine atoms are on opposite sides of the double bond, it is trans-1,2-dibromide.

Answer 2

The bromine is typically used as the halogenating reagent and the reaction is known as bromination of alkenes.

The general reaction is given as :

Alkene +
`Br_2` → 1,2-Dibromide

The stereochemistry of the alkene starting material is crucial because it determines the stereochemistry of the resulting 1,2-dibromide. The regiochemistry of the reaction is determined by Markovnikov's rule, which states that the bromine atom adds to the carbon atom with fewer hydrogen substituents. This leads to the formation of a more stable carbocation intermediate.

The bromination of alkenes is an example of an anti-addition reaction and we say that the two bromine atoms add to the carbon atoms of the double bond in a way that they end up on opposite sides (anti) of the resulting alkane.