Suppose benzene contained three distinct single bonds and three distinct double bonds. How many different structural isomers would there be for dichlorobenzene \(\left(\mathrm{C}_{6} \mathrm{H}_{4} \mathrm{Cl}_{2}\right)\) ? Draw all your proposed structures.

Structural isomerism occurs when molecules with the same molecular formula have different physical and chemical properties due to a difference in the arrangement of their atoms. When looking at dichlorobenzene (C6H4Cl2), which is a benzene molecule where two of the hydrogen atoms have been replaced by chlorine atoms, we see that structural isomerism plays a critical role.

There are three types of structural isomers: chain isomers, where carbon atoms connect differently; position isomers, where functional groups change positions; and functional group isomers, where the functional group itself changes. In the case of dichlorobenzene, we are concerned with position isomers. Specifically, the location of the chlorine atoms on the benzene ring varies, creating different compounds called 'ortho', 'meta', and 'para' isomers even though they share the same molecular formula.

The terms 'ortho', 'meta', and 'para' are used to describe the relative positions of substituents bonded to aromatic rings like that of benzene. These terms are particularly useful in discussing the isomers of benzene derivatives like dichlorobenzene.

In 'ortho' isomers, the substituents are adjacent to each other, that is on carbon atoms 1 and 2 of the benzene ring. 'Meta' isomers have substituents separated by a carbon atom, located on carbon atoms 1 and 3. Lastly, 'para' isomers have substituents directly opposite each other on the benzene ring, on carbon atoms 1 and 4. These configurations are not just important for nomenclature but also for the physical and chemical properties of the molecules. For instance, 'ortho' isomers might exhibit different boiling points compared to 'meta' and 'para' due to the close interaction of substituents causing different spatial arrangements of the molecule.

Benzene, a hydrocarbon with the formula C6H6, is a planar molecule that consists of six carbon atoms arranged in a hexagon with alternating single and double bonds. This structure creates a ring of electron density known as aromaticity, making benzene very stable and uniquely reactive. A benzene derivative occurs when one or more hydrogen atoms in benzene are replaced by other atoms or groups, resulting in compounds that retain the aromatic nature of benzene.

The dichlorobenzene isomers are examples of benzene derivatives. Each isomer - ortho, meta, and para dichlorobenzene - has distinctive properties and uses. For instance, para-dichlorobenzene is commonly used as a moth repellent and deodorizer due to its relatively high volatility, while ortho and meta isomers have found use in various organic syntheses. Understanding the structure of benzene and its derivatives is crucial for predicting reactivity and properties of these organic compounds.