Diazonium Salts — Prelims Strategy

Prelims Strategy

To excel in NEET questions on diazonium salts, a systematic approach is essential. First, thoroughly understand the diazotization reaction: its reagents ($NaNO_2/HCl$), conditions ($0-5^circ C$), and the formation of the arenediazonium salt.

Memorize the general formula $Ar-N_2^+ X^-$ and the key concept of $N_2$ as an excellent leaving group. Second, categorize the reactions into two main types: replacement reactions (where $N_2$ is lost) and coupling reactions (where $N_2$ is retained).

For replacement reactions, create a table or flowchart linking specific reagents to their products: e.g., $CuCl/HCl$ for $Ar-Cl$ (Sandmeyer), $HBF_4/Delta$ for $Ar-F$ (Balz-Schiemann), $H_3PO_2$ for $Ar-H$, $H_2O/Delta$ for $Ar-OH$.

Pay close attention to the copper reagents for Sandmeyer vs. Gattermann. For coupling reactions, remember the conditions: weakly alkaline for phenols and weakly acidic for anilines, and that they form azo dyes.

Practice predicting products for given reactants and reagents. For conceptual questions, focus on the stability differences between aliphatic and aromatic diazonium salts and the critical role of low temperature.

Be wary of trap options that swap reagents or conditions between similar reactions. Multi-step synthesis problems often feature diazonium salts as intermediates, so practice tracing the functional group transformations.