| Abstract
| - To understand the reactivity of acenes, particularly pentacene, the addition of HCl and water to aceneswas studied for the benzene−nonacene series at the B3LYP/6-31G(d) level of theory. Surprisingly, thereactivity of the acenes increases along the series up to hexacene and remains constant from hexaceneand above due to the biradical character of the ground state of higher acenes. While the exothermicityof HCl and water additions are very similar, the activation barriers for HCl and water additions differ bya constant factor of ca. 27 kcal/mol. The barrier for the addition of HCl varies from 44 kcal/mol forbenzene to 16−18 kcal/mol for pentacene−nonacene, whereas the barrier for the addition of water variesfrom 71 kcal/mol for benzene to 43−46 kcal/mol for pentacene−nonacene. The transition states (TSs)for the addition of water to acenes are relatively “late” on the reaction coordinate, compared to the“earlier” TSs for the addition of HCl. There is a substantial substituent effect on the energy barriers forthese reactions. HCl behaves as an electrophile, with ρHCl (vs σp) = −4.48 and −3.39 for anthracenesand pentacenes, respectively, while water behaves as a nucleophile, with ρH2O (vs σp) = 2.35 and 1.39for anthracenes and pentacenes, respectively.
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