SYNTHESIS AND CONFORMATIONAL-ANALYSIS OF NITROPOLYCYCLIC FLUORANTHENES

Nitroarenes are ubiquitous environmental pollutants some of which exhibit mutagenic and tumorigenic activities. The first systematic investigation of the nitration reactions of the polycyclic fluoranthenes, a major class of nonalternant polyarenes, is described. The specific hydrocarbons studied were benz[e]acephenanthrylene (1), benz[a]aceanthrylene (2), indeno[1,2,3-cd]pyrene (3), indeno[1,2,3-hi]chrysene (4), dibenz[a,e]aceanthrylene (5), dibenz[a,j]aceanthrylene (6), and dibenz[e,k]acephenanthrylene (7). The nitration of all hydrocarbons, except 1, proceeded with remarkable regioselectivity to provide a single mononitro product. In the case of 1, 17 % of a second mononitro isomer was isolated. The structures of the resulting mononitrofluoranthenes (8-15) were fully characterized by analysis of their high-resolution COSY, long-range COSY, and NOESY NMR spectra and by comparison with the spectra of the parent hydrocarbons. The observed nitration sites of the polycyclic fluoranthenes were in excellent agreement with theoretical predictions made by the DEWAR-PI method based on the relative energies of the Wheland intermediates for substitutions at various ring positions. The availability of the complete H-1 chemical shift assignments of the nitropolycyclic fluoranthenes (8-15), together with those of the parent hydrocarbons (1-7) and their UV-visible spectral data, enabled the molecular conformations of the nitro groups to be probed.