Stable Ion Studies of the Chrysene Skeleton. Protonation of Chrysene, 6-Halochrysenes, 6-Acetylchrysene, and 4H-Cyclopenta[def]chrysene:  NMR Studies of Charge Distribution in Chrysenium Cations and AM1 Calculations

Abstract

Chrysene (1), 6-fluorochrysene (2), 6-chlorochrysene (3), and 6-bromochrysene (4) are cleanly monoprotonated in FSO 3 H‚SbF 5 (ca. 10:1)/SO 2 ClF at the C-12 position. 6-Acetylchrysene (5) is CO-protonated in FSO 3 H/SO 2 ClF with significant charge delocalization into the chrysene and provides a model for a C-6-protonated chrysenium cation. 4H-Cyclopenta[def]chrysene (6) is protonated at C-5 (site of bromination and acetylation). The observed chrysenium (methanochrysenium) cations are those predicted by AM1 to have the lowest energies. The NMR characteristics of the resulting arenium ions are discussed and the ∆δ 13 Cs are compared with AM1 calculated changes in charges [∆q c ) q c (ion) -q c (neutral)]. Possible relationships between the charge delocalization path in chrysenium ions and metabolic activation of chrysenes by electrophilic pathways via the bay-region epoxide ring opening (f PAH-DNA adduct) are evaluated.

Charge Delocalization in Persistent Benz[a]anthracenium Cations BAH+ and Related α-Carbocations/Carboxonium Ions: Modeling Epoxide Ring Opening in Potent Carcinogens

“…In continuation of our work on PAH arenium ions, α-PAH-substituted carbocations as epoxide ring-opening models, and in a search for possible relationships between certain charge delocalization mode(s) in PAH-arenium ions and in α-PAH-substituted carbocations and magnitude of carcinogenicity, − we report the first direct study of a series of arenium ions derived from BA exploring the role of substituents and structure in directing electrophilic attack and the charge delocalization mode in the resulting carbocations (Figure ). To evaluate arenium ion character, carbocations 5 + , carboxonium ion 6H + (and dication 6H 2 2+ ) were generated as simplified models of bay-region epoxide ring opening, whereas carbocations 7 + , 9 + , and carboxonium ions 8H + and 10H + were generated as models of benzylic carbocation formation (at C-7), which bear some relationship to cholanthrylene−epoxide ring opening (Figure ) (see ref for details regarding the analogy).…”

Superacid‐Catalyzed Dimerization/Cyclization of Isopropenyl‐PAHs – Novel Pathways to PAH Dimers, Phenalenes and Their Stable Carbocations

“…favorable energetics of the chrysenium ion of protonation at C-6. [9,10] The DFT-optimized structure of 11b is shown in Figure S5. The computed angles between the average planes of the benzene rings in the optimized structures of 9b, 10b, and 11b (Table S1, Supporting Information) indicate that the pyrene and the chrysene skeletons remain planar in these dimers.…”

Probing the charge delocalization mode in methyl-, dimethyl- and methylene-bridged phenanthrenium ions. NMR studies of persistent mono- and di-cations and AM1 calculations

“…Similar observations have been made with other delocalized carbocations. 15, 32 Problems associated with a quantitative correlation have been addressed by Tolbert and Ogle 33 in the context of their work on delocalized carbanions. It is believed that the charge on carbon is exaggerated in AM1, since any quantitative meaning of Mulliken populations at this level of theory is uncertain.…”