Computation as a Prism: From Mechanistic Insight to Rational Reaction Design

Computational chemistry is often relegated to the final stages of a project, serving primarily as a visually appealing addition to a manuscript. When properly integrated, however, theoretical calculations offer far more than aesthetic value: they illuminate the mechanistic "black box" underlying experimental observations and provide a foundation for the rational design of future reactions. Through three published and unpublished case studies from our group, we demonstrate how computational analysis can deliver mechanistic insights that extend well beyond those accessible through experimental observation alone, evolving from a cosmetic afterthought into a powerful tool for guiding future experimental discovery. Specifically, we show how DFT calculations: (1) elucidated the origins of chemoselectivity of arylation reactions catalysed by bismuthonium salts; (2) rationalized catalyst-dependent switches between Friedel–Crafts alkylation and higher-order [8+2] cycloaddition; and (3) mapped a reaction sequence involving HB-mediated C–F activation followed by alkene insertion.