Write equations for the following reactions and identify the product formed in each case (i) chlorobenzene + sodium \(\stackrel{\text { ether }}{\longrightarrow}\) (ii) chlorobenzene \(+\) chloral \(\stackrel{\text { con. } \mathrm{H}_{2} \mathrm{SO}_{4}}{\longrightarrow}\)

The Wurtz-Fittig reaction is an important chemical process used to synthesize alkanes from aryl halides and alkyl halides in the presence of an alkali metal.
In the reaction between chlorobenzene and sodium, dry ether is used as a solvent, creating an environment which allows the sodium metal to react and effectively remove the chlorine atoms from chlorobenzene.

The mechanism involves the formation of free radicals or organosodium compounds, which then combine to form a new carbon-carbon bond, yielding the desired alkane along with a byproduct of sodium chloride (salt). The reaction is as follows:

• 2C₆H₅Cl + 2Na \( \stackrel{\text{ ether }}{\longrightarrow} \) 2C₆H₆ + 2NaCl

In this case, the product formed is benzene (C₆H₆). The Wurtz-Fittig reaction elegantly illustrates the concept of cross-coupling to form carbon-carbon bonds, a fundamental strategy in organic synthesis.
To further enhance understanding, visualization of the electron transfer during the process and the intermediate species involved can significantly aid students in grasping this reaction's concept.

Friedel-Crafts alkylation is another classic reaction in organic chemistry where an alkyl group is added to an aromatic ring. This typically requires the use of a Lewis acid catalyst, such as AlCl₃, FeCl₃, or in the exercise example, concentrated H₂SO₄.

The reaction between chlorobenzene and chloral in the presence of concentrated H₂SO₄ leads to the formation of 2,2,2-trichloroethylbenzene. Here, chloral serves as the alkylating agent, undergoing a transformation to attach its carbon group to the benzene ring.

• C₆H₅Cl + Cl₃CCHO \( \stackrel{\text{ con. H}_{2}\text{SO}_{4}}{\longrightarrow} \) C₆H₅CCl₃ + HCl + H₂O

One should note that unlike Wurtz-Fittig, Friedel-Crafts alkylation may introduce side reactions such as carbocation rearrangements leading to product mixtures. Discussing potential side reactions and how they are suppressed or avoided can be highly educational for students to understand this complexity.

Understanding the reaction mechanism is critical for mastering organic chemistry. It details the step-by-step sequence of elementary reactions by which overall chemical change occurs. The mechanism includes details about molecular rearrangements, the order of bond breakage and formation, and the role of catalysts.

For example, in the Wurtz-Fittig reaction, understanding the role of free radicals or anions in the reaction, and how they come together to create the final product is key to grasping the overall process. In Friedel-Crafts alkylation, comprehending how the Lewis acid catalyst activates the alkyl halide and generates a carbocation intermediate which then attacks the aromatic ring, is crucial.

A thorough analysis of the reaction mechanism can reveal information such as reaction intermediates, transition states, and kinetic aspects such as reaction rate. This is not just about memorizing the steps, but about visualizing and understanding the dance of electrons that underpins the chemistry. For students, building this molecular insight develops a strong foundation for predicting the outcomes of reactions and for designing new syntheses in the laboratory.