| Abstract
| - The first series of persistent carbocations derived from mono- and disubstituted chrysenes Ch (5-methyl- 3, 2-methoxy- 19, 2-methoxy-11-methyl- 20, 2-methoxy-5-methyl- 21, and 9-methyl-4H-cyclopenta[def]chrysene 22), monosubstituted benzo[c]phenanthrenes BcPh (3-methoxy- 23, 3-hydroxy- 24), and monosubstituted benzo[g]chrysenes BgCh (12-methoxy- 25; 12-hydroxy- 26) weregenerated in FSO3H/SO2ClF or FSO3H−SbF5 (4:1)/SO2ClF and studied by low-temperature NMRat 500 MHz. The methoxy and methyl substituents direct the protonation to their respective orthopositions. Whereas parent Ch 1 is protonated at C-6/C-12, 3 is protonated at C-6 (3aH+) and atC-12 (3bH+) with the latter being the thermodynamic cation. The 2-methoxy-Ch 19 is protonatedat C-1 to give two conformationally distinct carboxonium ions (19aH+/19bH+). In the disubstitutedCh derivatives 20 and 21, the 2-methoxy overrides the 5-methyl and the predominant carbocationsformed are via attack ortho to methoxy. For the methano derivative 22 (Me at C-9), a 3:1 mixtureof 22aH+/22bH+ is formed. For parent BcPh 13, nitration and benzoylation are directed to C-5.With 3-methoxy-BcPh 23, the site of attack moves to C-4, thus producing two conformationallydistinct carboxonium ions (23aH+/23bH+), whereas conventional nitration gave a 2:1 mixture of23aNO2 and 23bNO2. In 3-hydroxy-BcPh 24, the carboxonium ion 24H+ is exclusively formed. Forparent BgCh 16, protonation, nitration, and benzoylation are all directed to C-10 (16H+, 16NO2,16COPh), but presence of OMe or OH substituent at C-12 changes the site of attack to C-11. Chargedelocalization mode is probed based on magnitude of Δδ 13Cs and conformational aspects via NOEDexperiments. Complete NMR data are also reported for several benzoylation/nitration products.Using ab initio/GIAO (and NICS), the NMR chemical shifts (and aromaticity) in model carbocationsA−D were evaluated. This work represents the first direct study of the carbocations derived fromthe methyl-, methoxy-/hydroxy-derivatives of three important classes of bay-region and fjord-regionPAHs whose diol-epoxides extensively bind to DNA. It also extends the available data on electrophilicchemistry of BcPh and BgCh.
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