Question

Draw structural formulas for the two constitutional isomers with the molecular formula \(\mathrm{C}_{5} \mathrm{H}_{6} \mathrm{Br}_{2}\) formed by adding one mole of \(\mathrm{Br}_{2}\) to cyclopentadiene.

Short answer

Question: Draw the structural formulas of two constitutional isomers of C5H6Br2 formed by adding one mole of Br2 to cyclopentadiene. Answer: The two constitutional isomers have the following structures: Isomer 1: ``` H H \ / C - C Br / \ / C C Br \\ / C = C / \ H H ``` Isomer 2: ``` H H \ / C=C // \ C C - Br \ // \ C - Br H / \ H H ```

Step-by-step solution

Identify the structure of cyclopentadiene

Cyclopentadiene's molecular formula is \(\mathrm{C}_{5} \mathrm{H}_{6}\) and consists of a five-membered ring with two double bonds. The structure can be drawn as: ``` H H \ / C=C // \ C C \ // C=C / \ H H ```

Determine the mechanism of the reaction with \(\mathrm{Br}_{2}\)

When \(\mathrm{Br}_{2}\) is added to a double bond, the double bond is broken, and a \(\mathrm{Br}\) atom adds to each carbon atom that was originally part of the double bond. This reaction is called an electrophilic addition. Since there are two double bonds in cyclopentadiene, \(\mathrm{Br}_{2}\) can add to one of the double bonds - creating two products where the bromine atoms are added to different carbon atoms.

Draw the two isomers formed from the reaction

When one mole of \(\mathrm{Br}_{2}\) is added to cyclopentadiene, two constitutional isomers are formed. Here are their structures: Isomer 1 - The bromine atoms are added to the two carbon atoms of the first double bond: ``` H H \ / C - C Br / \ / C C Br \\ / C = C / \ H H ``` Isomer 2 - The bromine atoms are added to the two carbon atoms of the second double bond: ``` H H \ / C=C // \ C C - Br \ // \ C - Br H / \ H H ``` These are the two constitutional isomers formed by adding one mole of \(\mathrm{Br}_{2}\) to cyclopentadiene. Both have the molecular formula \(\mathrm{C}_{5} \mathrm{H}_{6} \mathrm{Br}_{2}\).