Chapter 20: Problem 21

Draw structural formulas for the two constitutional isomers with the molecular formula \(\mathrm{C}_{5} \mathrm{H}_{4} \mathrm{Br}_{2}\) formed by adding one mole of \(\mathrm{Br}_{2}\) to cyclopentadiene.

Short Answer

Expert verified

The two constitutional isomers that result from the addition of one mole of Br2 to cyclopentadiene are: Isomer 1: ``` C = C - C / \ C =C C | \ / Br-C Br ``` Isomer 2: ``` C - C = C Br | \ / C C \ / C =C - Br ```

Step by step solution

Draw the structure of cyclopentadiene

Cyclopentadiene is a five-membered ring with two double bonds, which makes it an unsaturated hydrocarbon. Its structure can be represented by the following skeletal formula: ``` C = C - C / \ C C \ / - C =C ``` Next, we need to see how a single mole of \(\mathrm{Br}_{2}\) can be added to this structure to get two constitutional isomers.

Add the first bromine atom to the structure

Addition of the first \(\mathrm{Br}\) atom from \(\mathrm{Br}_{2}\) can be done in two ways. The first way is to break one of the double bonds and add the \(\mathrm{Br}\) atom to one of the carbon atoms involved in the double bond. The second way is to add the \(\mathrm{Br}\) atom to one of the other three carbon atoms in the ring. We will consider both of these scenarios.

Based on the addition of the first \(\mathrm{Br}\) atom, draw both possible intermediate structures

Considering the addition of the first \(\mathrm{Br}\) atom to either site, the two following intermediate structures can be formed: Intermediate Structure 1: ``` Br | C = C - C C | \ \ / C C =C / \ / C ``` Intermediate Structure 2: ``` C = C - C / | \ C | C Br C =C / \ / C ```

Determine both possibilities for the addition of the second \(\mathrm{Br}\) atom

Now, we add the second \(\mathrm{Br}\) atom from \(\mathrm{Br}_{2}\) to the structures obtained in Step 3. The second \(\mathrm{Br}\) atom can be added to any of the remaining carbon atoms with a free valence, giving us two final constitutional isomers.

Draw the two constitutional isomers for the given molecular formula

Taking the possibilities obtained in Step 4, we can now draw the two constitutional isomers formed by adding \(\mathrm{Br}_{2}\) to cyclopentadiene. Isomer 1: ``` C = C - C / \ C =C C | \ / Br-C Br ``` Isomer 2: ``` C - C = C Br | \ / C C \ / C =C - Br ``` Following these steps, we have drawn the structural formulas for the two constitutional isomers with the molecular formula \(\mathrm{C}_{5} \mathrm{H}_{4} \mathrm{Br}_{2}\) formed by adding one mole of \(\mathrm{Br}_{2}\) to cyclopentadiene.

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Draw structural formulas for the two constitutional isomers with the molecular formula \(\mathrm{C}_{5} \mathrm{H}_{4} \mathrm{Br}_{2}\) formed by adding one mole of \(\mathrm{Br}_{2}\) to cyclopentadiene.

Short Answer

Step by step solution

Draw the structure of cyclopentadiene

Add the first bromine atom to the structure

Based on the addition of the first \(\mathrm{Br}\) atom, draw both possible intermediate structures

Determine both possibilities for the addition of the second \(\mathrm{Br}\) atom

Draw the two constitutional isomers for the given molecular formula

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