Organic Chemistry MCAT Practice Exam 2025 - Free MCAT Practice Questions and Study Guide

The Diazonium coupling reaction is known for producing a yellow precipitate when aromatic compounds are involved. In this reaction, an aryl diazonium salt reacts with another aromatic compound, typically a phenol or another aromatic amine, to form a biaryl compound. This coupling can yield colorful products due to the extended conjugation in the resulting structure.

A characteristic aspect of these reactions is that many of the products are colored, and the yellow precipitate commonly observed indicates the formation of these conjugated systems, which possess distinct absorbance properties. The color can serve as a visual indicator of the successful formation of the product.

The other reactions listed do not typically lead to the formation of colored precipitates in the same context. Grignard reactions usually involve the nucleophilic addition of a Grignard reagent to a carbonyl compound, while Friedel-Crafts reactions focus on alkylation or acylation of aromatic compounds without producing solid precipitates that change the color of the solution. Addition reactions refer to a broad range of mechanisms that add across double or triple bonds but do not have the specific coloration associated with diazonium coupling. Thus, the unique mechanism of diazonium coupling is what leads to the distinctive yellow precipitate, making