What is the product of the reaction given below ? Cyclohexene $+ Br_2 \xrightarrow{heat, u.v. light}$

Question

Accepted Answer

The reaction in question involves cyclohexene reacting with bromine ($Br_2$) under the influence of heat and ultraviolet (u.v.) light. This setup typically leads to a free radical halogenation process rather than an addition reaction. Let's analyze why Option 1 is the correct answer and why the other options are incorrect.

1. **Option 1: 1,2-Dibromocyclohexane**  
   In the presence of heat and u.v. light, bromine can undergo a free radical substitution reaction with cyclohexene. The double bond in cyclohexene can react with bromine to form a dibrominated product. The most straightforward outcome of this reaction is the addition of bromine across the double bond, resulting in 1,2-dibromocyclohexane. This is consistent with the typical behavior of alkenes reacting with bromine under these conditions, where the double bond is broken, and each carbon atom of the former double bond forms a bond with a bromine atom.

2. **Option 2: 3-Bromocyclohexene**  
   This option suggests a monobromination at the allylic position (position 3), which is not the primary reaction pathway under the given conditions. The presence of heat and u.v. light favors the addition of bromine across the double bond rather than allylic bromination. Therefore, this option is incorrect.

3. **Option 3: 1-Bromocyclohexane**  
   This option implies a single bromine atom addition, which would typically occur in a radical substitution reaction at the allylic position. However, the conditions specified (heat and u.v. light) are more conducive to the addition of bromine across the double bond, leading to a dibrominated product rather than a monobrominated one. Thus, this option is incorrect.

4. **Option 4: Bromobenzene**  
   This option is incorrect because cyclohexene is not aromatic and cannot be converted into bromobenzene through the reaction conditions provided. Bromobenzene is a completely different compound that would require an aromatic ring, which cyclohexene does not possess. Therefore, this option is not feasible in the context of the given reaction.

In conclusion, the reaction conditions favor the addition of bromine across the double bond of cyclohexene, resulting in the formation of 1,2-dibromocyclohexane, making Option 1 the correct answer.