Question

Identify the product formed when 2‐cholestene is treated with Br₂:

• A. 5β, 6α‐dibromocholestane
• B. 2β, 3α‐dibromocholestane
• C. 5α, 6β‐dibromocholestane
• D. 5α, 6β‐dibromo 3β‐hydroxy cholestane

Answer 1

The Correct Option is B

The problem involves determining the product when 2‐cholestene is treated with bromine (Br₂). This reaction is a typical addition reaction where bromine adds across the double bond of the alkene.

Step 1: Understand the Structure of 2-Cholestene

2-Cholestene is an alkene derivative of cholesterol. It has a double bond between the carbon atoms at positions 2 and 3 in the cholesterol framework.

Step 2: Reaction Mechanism with Br₂

In the presence of bromine, the double bond in 2-cholestene will undergo an addition reaction. The addition of Br₂ across the double bond occurs, forming a vicinal dibromide.

Step 3: Identify the Proper Stereochemistry

The addition of bromine to an alkene often leads to anti-addition, owing to the formation of a bromonium ion intermediate. This stereochemistry ensures that the bromine atoms add to opposite sides of the former double bond.

For 2-cholestene, this will result in 2β, 3α-dibromocholestane, where one bromine atom adds to the carbon at the 2 position in the β orientation, and the other bromine atom adds to the carbon at the 3 position in the α orientation.

Conclusion:

The product formed when 2-cholestene is treated with Br₂ is 2β, 3α‐dibromocholestane. This is because of the vicinal anti-addition of bromine across the double bond present between positions 2 and 3 of the cholestene.