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Second‐order rate constants for the Diels‐Alder reaction of aromatic hydrocarbons comprising up to 13 condensed benzene rings with maleic anhydride have been measured under standardized conditions. The position of attack was deduced from the UV spectra of the adducts. A number of theoretical models was examined as to how far they reproduce the observed rate data and positional selectivities. All except Fukui's frontier orbital concept were successful. These include Brown's para‐localization model, second‐order perturbation theory using Hückel orbital energies and AO coefficients, Clar's sextet theory and Herndon's structure count method. The latter two models provide a particularly attractive basis for discussing structure/reactivity relationships. Inter alia, they lead to the discovery of “isocanonical” series, i.e., to homologous series in which corresponding members have the same theoretical reactivity index and therefore the same rate constant, despite widely differing topologies.

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