Abstract: Electrophilic aromatic halogenation (SEAr) represents a fundamental concept in undergraduate organic chemistry curricula, serving as a cornerstone for teaching electronic effects, directing effects, and other core principles. Recent advancements in synthetic chemistry have expanded the scope of aromatic halogenation to include metal-catalyzed and photocatalytic approaches. This work builds upon our group’s research published in Nature Chemistry, providing a pedagogical comparison between classical iron-catalyzed electrophilic aromatic halogenation and the emerging photochemical iron-catalyzed denitrative halogenation. The case study demonstrates how photoexcited iron complexes can generate chlorine radicals through ligand-to-metal charge transfer (LMCT) processes, enabling the direct conversion of nitrobenzene to chlorobenzene - a transformation challenging to achieve via conventional methods. Furthermore, we propose instructional strategies that integrate traditional content with contemporary case studies, guiding students from familiar structure-reactivity frameworks toward advanced understanding of reaction selectivity, thereby cultivating scientific thinking.

Key words: Aromatic halogenation, Iron catalysis, Organometallic chemistry, Undergraduate chemistry education