Myths and Truths About Electrophilic Aromatic Substitution: The Particular Case of Fluorobenzene

ABSTRACT Electrophilic aromatic substitution (EAS) is a fundamental reaction introduced early in organic chemistry courses, highlighting the influence of substituents on reactivity and regioselectivity in benzene rings. This study revisits and challenges established concepts about the thermodynamics of nitration EAS, particularly the formation of the σ ‐complex intermediate, and reexamines the role of halogens traditionally classified as deactivating, ortho‐para ‐directing groups. Our findings reveal that the initial step of the reaction is exothermic and that F, Cl, and Br substituents enhance EAS reactivity at the para position compared to hydrogen. These insights suggest a need for updating organic chemistry textbooks to provide a more accurate and nuanced description of substituent effects, especially those of halogens, on the characteristics of EAS reactions.