Question

1. Write chemical equations to illustrate the reactions of bromine with cyclohexane, toluene, chlorobenzene, and cyclohexane (NR if no reaction)

2. What type of reaction is occurring between cyclohexane and potassium permanganate? What is the brown precipitate formed from the reaction?

3. You may have seen some reactions of bromine with toluene. Compare this with your observations of the reaction of bromine with chlorobenzene. Based on the structure of toluene where do you think the reaction occurred (aromatic ring or side chain)? Is this reaction similar to the reaction of bromine with an alkane or an alkene? Explain.

Answer 1

1.The glass on the left contains cyclohexane, an alkane with the formula C₆H₁₂. The glass on the right contains cyclohexene, an alkene which has the formula C₆H₁₀.

An addition reaction occurs when halogens are added to alkenes, but not to alkanes. The following reaction occurs when Br2 is added to cyclohexene:

C6H10 + Br2 ----> C6H10Br2

One bromine atom adds to each side of the double bond, which opens to form two new single bonds. You can see the reaction occur because the red color of Br2disappears as it forms the colorless alkyl halide.

Bromine is not able to react with cyclohexane by substitution, and there are no double bonds for an addition reaction, so no reaction occurs:

C6H12 + Br2 ----> N.R.

You can tell that no reaction has occurred because the red color of Br2 remains.

2.

As mentioned above, saturated hydrocarbons will only react with bromine under free radical conditions, meaning you have to add UV light. So simply adding some bromine to cyclohexane won