Clar's Aromatic Sextet Theory Revisited via Molecular Electrostatic Potential Topography

Abstract

Full characterization of the molecular electrostatic potential (MESP) topography of the π-regions of 12 polycyclic benzenoid hydrocarbons (PBHs) is carried out. Benzene is endowed with the most perfect circular distribution of π-delocalization, and the hexagonal rings of other systems possess varying degrees of lesser π-delocalization. The topographical features describe Clar's aromatic sextet theory very well and simplify the aromatic characterization of each ring of a PBH system. The concepts such as “aromatic dilution” observed for polyacene series and the “empty ring” in triphenylene, perylene, and coronene are clearly brought out from this study. The positions of (3, +3) critical points (CPs) are always observed very close to shorter bonds, providing valuable hints at how the π-electrons are shared among the carbons. Further, average values of the MESP at CPs calculated for each ring ( ) and for the whole molecule ( ) bear linear correlation with the local aromaticity values estimated by Li and Jiang and the hardness values reported by Zhou and Parr for the global aromaticity, respectively. Thus the mapping of the MESP topography provides an elaborate characterization of the π-regions of PBH systems and a description of the intimately connected aromaticity.

Application of Electron Delocalization Indicators in the Study of Electrophilic Aromatic Substitution Reactions

“…The results of the analysis of the indices , BOIA and FLU are consistent with those of Suresh and coworkers [109] who found and characterize the critical points of the Molecular Electrostatic Potential (MESP),…”

Thienoacene‐Based Organic Semiconductors

“…The comparison of the electronic structures of hydrocarbonbased linear "acenes" and kinked "phenes" and the higher stability of the latter due to the low-lying HOMO and the high-lying lowest unoccupied molecular orbital (LUMO) energy levels are documented in detail from a theoretical point of view. [ 18 ] It is clearly demonstrated from these considerations that semiconductors that have HOMO energy levels lower than 5.0 eV. [ 21 ] Along with these criteria, the present thienoacenes seem to be promising candidates for the development of airstable OFETs.…”

Synthesis, characterization and structural aspects of new haptens for PAHs

“…The dihedral angle of the anthracene ring and the R 2 2 (8) graph-set motif is 80.08°. According to the X-ray data in Table 4, the bond lengths and angles of the corresponding parts of I and II are almost same with those of naphthalene and anthracene [12]. The biggest difference between I and naphthalene is 0.0099 Å at (C 7 -C 12 ), while between II and anthracene is 0.0311 Å at (C 12 -C 13 ), respectively.…”

“…PAHs have received considerable attention because of their rich chemistry [1][2][3][4][5], physical properties [6], technological and industrial applications [1], aromaticity [7][8][9][10][11][12][13][14][15], and role as a major class of environmental pollutants and carcinogens [16][17][18].…”