The Anomalous Reactivity of Fluorobenzene in Electrophilic Aromatic Substitution and Related Phenomena

• Published in: Journal of chemical education Vol. 80; no. 6; p. 679
• Main Authors: Rosenthal, Joel, Schuster, David I
• Format: Journal Article
• Language: English
• Published: Easton Division of Chemical Education 01.06.2003; American Chemical Society
• Subjects: Chemical reactions; Chemistry; Deactivation; Halobenzenes; Halogens; Reactivity; Substitution reactions; Textbooks; Textbooks / Reference Books; Continuing Education; Research: Science and Education; Aromatic Compounds; Organic Chemistry
• ISSN: 0021-9584; 1938-1328
• DOI: 10.1021/ed080p679

Fluorobenzene (PhF) displays a reactivity in electrophilic aromatic substitution (EAS) that is, at first glance, anomalous in comparison to the reactivity of the other halobenzenes. This is borne out by the fact that the rates of typical EAS reactions on PhF, such as nitration and chlorination, are 15–80% as fast as that of benzene while the same reactions on the other halobenzenes are five to ten times slower than that of PhF. Most striking, however, is the fact that reactions at the para position of PhF are typically faster than the corresponding reactions at a single position of benzene. Furthermore, EAS on PhF results in ∼ 90% of the para-substituted product, while the other halobenzenes give ratios of ortho- and para-substituted products that are closer to the simple statistical distribution. These striking observations are not discussed or, for that matter, even reported in introductory or advanced textbooks of organic chemistry and are clearly not compatible with the typically superficial textbook discussions of this subject. New models incorporating the interplay of inductive stabilization and resonance effects involving fluorine can be used to explain not only these counterintuitive experimental observations but also other interesting facets of organofluorine chemistry.