An important observation supporting the concept of resonance in the localized electron model was that there are only three different structures of dichlorobenzene \(\left(\mathrm{C}_{6} \mathrm{H}_{4} \mathrm{Cl}_{2}\right)\). How does this fact support the concept of resonance? (See Exercise \(91 .\) )

The concept of resonance in the localized electron model refers to a situation where a molecule or ion can be represented by more than one Lewis structure which cannot be interconverted. These different Lewis structures, called resonance structures, are used to describe the real molecule's electronic structure better. The actual molecule or ion is considered a hybrid of all these resonance structures, and this hybrid can often have properties that are a blended average of the individual structures.

We need to draw the three different structures of dichlorobenzene, which has a chemical formula C6H4Cl2. 1. Ortho-dichlorobenzene (o-dichlorobenzene): Two chlorine (Cl) atoms are attached to two adjacent carbon atoms in the benzene ring. 2. Meta-dichlorobenzene (m-dichlorobenzene): Two chlorine (Cl) atoms are attached to two carbon atoms in the benzene ring that have one carbon atom between them. 3. Para-dichlorobenzene (p-dichlorobenzene): Two chlorine (Cl) atoms are attached to two carbon atoms in the benzene ring that are directly opposite to each other.

The concept of resonance helps explain the observation of having only three different structures of dichlorobenzene. In benzene, which is the base molecule for dichlorobenzene, the electrons in the double bonds are delocalized, meaning they are distributed across all six carbon atoms. This means that these electrons can be shared between all carbon atoms, causing the molecule to exhibit resonance structures with the double bonds at different positions within the ring. The observation of only three different dichlorobenzene structures implies that, depending on the position of the Cl atoms in the benzene ring, the electron delocalization and resonance can still occur. If the electron delocalization within the benzene ring got disrupted, more individual structures would have had different properties, leading to more observed dichlorobenzene isomers. In conclusion, the fact that there are only three different structures of dichlorobenzene supports the concept of resonance in the localized electron model. This is because the delocalization of electrons within the benzene ring allows the molecule to maintain its resonant nature, making the different structures similar in terms of properties that are affected by electron delocalization.