Theoretical (DFT, GIAO–NMR, NICS) study of carbocations (M+H)+, dications (M2+) and dianions (M2−) from dihydro-dicyclopenta[ef,kl]heptalene (dihydro-azupyrene), dihydro-dicyclohepta[ed,gh]pentalene, and related bridged [14]annulenes

Abstract

The annulenium ions of protonation, the two-electron oxidation dications, and the two-electron reduction dianions derived from dihydro- and dimethyldihydro derivatives (cis and trans) of dicyclopenta[ef,kl]heptalene (azupyrene) (1) and dicyclohepta[ed,gh]pentalene (2), which are the nonalternant isomers of pyrene, were studied by density functional theory (DFT) at the B3LYP/6-31G(d), 6-31+G(d,p), or 6–31++G(d,p) levels. Charge delocalization modes in the energetically most favored annulenium ions, as well as in the singlet and triplet dications and dianions, were assessed based on gauge-including atomic orbital (GIAO) Δδ¹³C values and via changes in natural population analysis (NPA) charges. Relative aromaticity/antiaromaticity in the annulenes were gauged via nucleus-independent chemical shift (NICS) and ΔNICS. Annulenium ions of monoprotonation, the dications, and dianions derived from bismethano- and propanediylidene [14]annulenes were also studied by DFT for comparison with the cis-dihydro isomers derived from 2. Computed GIAO NMR data and the optimized geometries were compared with the experimental data when available, and the optimized geometries were compared with the X-ray data if known. A basis-set dependency study of the computed GIAO chemical shifts was also undertaken. The present DFT work represents the first detailed comparative theoretical study of charged annulenes derived from the dihydro derivatives of 1 and 2.