| Abstract
| - In connection to a growing interest in developing structure/activity trends in nonalternantpolyarenes, we report on the generation and NMR studies of the first series of persistent areniumions from large methylene-bridged PAHs (mostly 22π six-fused ring systems). Low-temperatureprotonation (FSO3H/SO2ClF) and model nitration (with HNO3/HOAc or NO2+ BF4-) were used asmimic reactions for generation of biological electrophiles. The site(s) of protonation (and nitration)were determined as a function of PAH structure. Charge delocalization mode in the resultingarenium ions of protonation are assessed based on detailed low-temperature NMR studies at 500MHz. Systems studied were 1-methylcyclopenta[def]phenanthrene 2, 11H-benz[bc]aceanthrylene8, 5H-benzo[b]cyclopenta[def]chrysene 9, 13H-dibenzo-[bc,l]aceanthrylene 10, 13H-cyclopenta[rst]pentaphene 11, 4H-benzo[b]cyclopenta[mno]chrysene 12, 6H-cyclopenta[ghi]picene 13, 4H-cyclopenta[pqr]picene 14, 4H-cyclopenta[def]dibenz[a,c]anthracene 15. For comparison, dibenzo[a,c]anthracene 16 and dibenzo[a,h]anthracene 17 were also included (Figures and ). It is shownthat the methano-bridge exerts a strong directive effect which diminishes as the bridge movesfrom the more central “inner” positions to more peripheral “outer” positions. Charge delocalizationmode in the resulting carbocations are discussed based on the magnitude of Δδ 13C values. Possiblerelationships with biological electrophiles formed by epoxide ring opening in the putative metabolitesare also considered.
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