Large PAHs Derived from Benzanthrone and Naphthanthrone. A Semiempirical Study

Abstract

In a systematic semiempirical study, AM1 and PM3 methods are employed to calculate minimum, transition state, and higher order saddle point conformations of planar and overcrowded C34H18 4–15 and C38H18 16–21 LPAHs, potential products of peri - peri reductive coupling of benzanthrone (2) and naphthanthrone (3), respectively. The most stable LPAHs in these series are planar C2v-4 (C34H18) and twisted - folded C2-21 (C38H18). Among overcrowded regions, two coves are consistently more destabilizing than one fjord, according to both semiempirical methods. The non-planar members of the C34H18 and C38H18 series adopt twisted - folded conformations as global minima and folded - twisted conformations as transition states. The barriers for enantiomerization of the LPAHs with a fjord, cove, and two coves are 18.5–24.0 (AM1) and 16.0–19.3 (PM3), 11.1–11.8 (AM1) and 7.2–7.5 (PM3), 12.0–12.4 (AM1) and 8.1–8.4kcal/mol (PM3), respectively. A comparison of calculated and experimentally determined geometries of LPAHs shows a good correlation between the two types of methods.