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 89)?

Resonance is a concept in chemistry where a molecule does not have a single, well-defined structure, but rather exists as a hybrid of several structures, which are called resonance structures. These structures have individual contributing effects, so the overall structure of the molecule is a mixture of all the possible resonance structures. The localized electron model is an approach to understanding the structure and bonding in molecules. In this model, electrons are assumed to be localized around specific atoms or between a pair of atoms, forming single, double, or triple bonds.

Dichlorobenzene (C6H4Cl2) has three different structures due to the different possible positions of chlorine atoms on the benzene ring: 1. Ortho-dichlorobenzene: The two chlorine atoms are bonded to adjacent carbon atoms on the benzene ring. 2. Meta-dichlorobenzene: The two chlorine atoms are bonded to carbon atoms separated by one carbon atom. 3. Para-dichlorobenzene: The two chlorine atoms are bonded to carbon atoms separated by two carbon atoms (opposite sides of the benzene ring).

The concept of resonance is supported by the fact that there are only three different structures of dichlorobenzene, as each structure represents a different way that the two chlorine atoms can be positioned on the benzene ring. This limited number of structures implies that electrons are localized and the possible bonding configurations are limited. In the localized electron model, the electrons involved in bonding are confined to specific regions or orbitals, resulting in localized structures. The fact that only three structures are found for dichlorobenzene indicates that the electrons are localized in such a way that only these specific structures can form. Furthermore, if the electrons were not localized, many more structures would be possible, as the electrons could be distributed evenly around the benzene ring. However, the limited number of structures observed for dichlorobenzene supports the localized electron model, and this, in turn, supports the concept of resonance, as the different structures of dichlorobenzene can be seen as resonance structures that contribute to the overall description of the molecule.