The title of this post comes from an article published in a special virtual issue on the theme “Physical Organic Chemistry: Never Out of Style“[1] There, Paul Rablen presents the case that the amount of o (ortho) product in electrophilic substitution of a phenyl ring bearing an EWG (electron withdrawing group) is often large enough to merit changing the long held rule-of-thumb for EWGs from being just meta directors into these substituents are best understood as ortho, meta-directors, with a preference for meta. I cannot help but add here a citation[2] to the earliest publication I can find showing tables of both o,p and m-directing groups and dating from 1887, so this rule is 138 years old (at least).
References
- P.R. Rablen, "Typical Electron-Withdrawing Groups Are <i>ortho</i>, <i>meta</i>-Directors Rather than <i>meta</i>-Directors in Electrophilic Aromatic Substitution", The Journal of Organic Chemistry, vol. 90, pp. 6090-6093, 2025. https://doi.org/10.1021/acs.joc.5c00426
- H.E. Armstrong, "XXVIII.—An explanation of the laws which govern substitution in the case of benzenoid compounds", J. Chem. Soc., Trans., vol. 51, pp. 258-268, 1887. https://doi.org/10.1039/ct8875100258