In which of the following reactions, Ethylbenzene is not formed as the final product? (a) \(\mathrm{C}_{6} \mathrm{H}_{6}+\mathrm{CH}_{2}=\mathrm{CH}_{2} \stackrel{\mathrm{H}_{3} \mathrm{PO}_{4}}{\longrightarrow}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Br}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br} \underset{\text { ether }}{\stackrel{\mathrm{Na}}{\longrightarrow}}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{CH}_{3}+\mathrm{CH}_{3} \mathrm{Cl} \stackrel{\mathrm{AlCl}_{3}}{\longrightarrow}\)

The Friedel-Crafts alkylation reaction represents a cornerstone in the synthesis of aromatic compounds. This reaction involves adding an alkyl group to an aromatic ring. Specifically, it uses a Lewis acid catalyst, like aluminum chloride (\textbf{AlCl}\(_3\)), to facilitate the attachment of a carbon group from an alkyl halide to the benzene ring.

The power of this reaction lies in its versatility, allowing chemists to manipulate the structure of benzene by attaching various-sized carbon chains. However, its limitation is worth noting. It may lead to polyalkylation, where multiple alkylation events happen, potentially driving the reaction away from the desired product. In the case of the textbook exercise, toluene reacted with methyl chloride, not to form ethylbenzene, but rather, a disubstituted benzene derivative. Here, the presence of a \textbf{CH}\(_3\) group on the benzene ring activates it towards further alkylation, explaining why ethylbenzene is not the outcome.

The Wurtz-Fittig reaction is a lesser-known but valuable tool for creating a bond between an alkyl group and an aryl group. In this coupling reaction, an aryl halide like bromobenzene reacts with an alkyl halide in the presence of sodium metal. The result is a direct pathway to substituted benzene rings that might otherwise be difficult to create.

Such reactions are performed in dry ether, providing a nonpolar solvent to stabilize the intermediates. The utility of the Wurtz-Fittig reaction is highlighted in the textbook example, where ethyl bromide couples with bromobenzene to synthesize ethylbenzene efficiently. Students should recognize the specificity of this reaction – it's a powerful method to marry the aromatic character of benzene with varied alkyl chains, integral in the field of organic synthesis.

Alkene addition reactions are a fundamental transformation in organic chemistry. These reactions involve breaking the pi bond of an alkene to make room for new attachments—typically atoms or groups of atoms—across the double bond. Such reactions are diverse and include hydration, hydrogenation, and halogenation, among others.

In the context of forming ethylbenzene, the addition reaction involves benzene reacting with ethylene in the presence of an acid catalyst like phosphoric acid (\textbf{H}\(_3\)\textbf{PO}\(_4\)). This reaction method is attractive due to its regioselectivity, referred to as Markovnikov's rule, where the more substituted carbon becomes the favored attachment point for the new group. The method demonstrated in the exercise showcases a straightforward reaction that adds an ethyl group to the benzene, forming ethylbenzene, highlighting the simplicity and effectiveness of alkene addition reactions in producing alkylated aromatic compounds.