Carbocations from dibenz[a,j]anthracene and dibenz[a,h]anthracene, their methylated derivatives, and oxidized metabolites: A stable ion and DFT study

Abstract

Parent dibenz [a,j]anthracene DB [a,j]A 1 is protonated (in TfOH/SO 2 ClF) to give a 1:1 mixture of meso-protonated arenium ions 1aH + and 1bH + . The 7-methyl-DB[a,j]A 2 is protonated (in FSO 3 H/SO 2 ClF or TfOH/SO 2 ClF) at the unsubstituted meso position (C-14) to give 2H + , and the 7,14-dimethyl derivative 3 is ipso-protonated (in FSO 3 H/SO 2 ClF) at C-14 to give 3H + .Experimental and/or GIAO-NMR derived ∆δ 13C values, as well as changes in the computed NPA charges, were used to derive charge delocalization maps for the protonated carbocations derived from parent and methylated DB[a,j]A and DB[a,h]A. DFT and GIAO-DFT were also employed to model the bay-region anti-diol-epoxides (DEs), their derived carbocations, and model covalent adducts. The higher tumorigenic potenties of DB[a,h]A and its methylated derivatives as compared to those of DB [a,j]A are reflected in relative ease of carbocation formation from the DEs. Preference for anti stereochemistry in the covalent adducts derived from DB[a,h]A increases with increasing steric crowding at the bay-region.