One early problem with the Kekulé structure was that only one 1,2 -disubstituted isomer of benzene could be found for any given substituent. That is, there is only one 1,2 -dimethylbenzene (o-xylene). Explain why this observation would have been hard for Kekulé to explain.

These p electrons are delocalized over the entire ring, which means they can freely move across all six carbon atoms. This delocalization contributes significantly to the overall stability of benzene, a property known as aromaticity.
The idea of delocalized electrons contrasts sharply with the initial Kekulé structure, which depicted fixed alternating single and double bonds. Understanding delocalization helps explain the observed chemical behaviors, such as the lack of multiple isomers for 1,2-disubstituted benzenes. Because the electrons are evenly distributed, the positions of substituents become equivalent, preventing the formation of distinct isomers predicted by a model with fixed bonds.

In an organic chemistry context, learning about benzene also involves understanding its reactivity, especially in electrophilic substitution reactions. These reactions highlight benzene's role as a building block for more complex organic molecules. When Kekulé proposed his model of benzene, it laid the groundwork for future chemists to explore and eventually understand the true nature of aromatic compounds.
Concepts like resonance and delocalization not only clarify the structure of benzene but also enhance our understanding of the stability and reactivity of many compounds studied in organic chemistry. Consequently, knowledge about benzene and its properties is essential for students and professionals involved in chemical research and industry.