Local Aromaticity in Benzo- and Benzocyclobutadieno-Annelated Phenanthrenes

Abstract

The effects of benzo-and benzocyclobutadieno-(BCBD-)annelation on the local aromaticity of the central ring (X) of phenanthrene were examined. The local aromaticity of the ring X was estimated using a graph-theory-based index and two geometrybased indices. DFT calculations of phenanthrene congeners showed that many of these molecules are nonplanar, with significant steric strain. All three indices indicate that the effect of benzo-annelation is opposite to that of BCBD-annelation. The deviation of some phenanthrene derivatives from planarity does not influence the effects of annelation. This finding is in accord with some previously reported studies on the dependence of the aromaticity of the ring(s) on distortion from planarity.

Phenylated Benzotetraphenes (Dibenzanthracenes) by Nickel-Catalyzed Diphenylacetylene Cycloadditions to Linear [3]Phenylenes

“…13 While the presence of the silyl groups compromises a strict comparison of the bond distances in 8b with those of 4, 7 their perturbing substituent effect tapers off rapidly beyond the ring of attachment, 14 justifying a cautious structural evaluation of the relative aromaticity of the central phenanthrene ring. Gratifyingly, and in consonance with computational predictions (vide supra), 11 the averaged sum of its C-C bond lengths decreases along the series 4 (1.437 Å), 7 9,10-diphenylphenanthrene (1.428 Å), 15 and 8b (1.423 Å), a tentative sign of increasing delocalization. 11 Similarly, the average deviation of these distances from that of benzene (1.388 Å), also decreases (0.334, 0.276, and 0.247 Å, respectively).…”

“…Gratifyingly, and in consonance with computational predictions (vide supra), 11 the averaged sum of its C-C bond lengths decreases along the series 4 (1.437 Å), 7 9,10-diphenylphenanthrene (1.428 Å), 15 and 8b (1.423 Å), a tentative sign of increasing delocalization. 11 Similarly, the average deviation of these distances from that of benzene (1.388 Å), also decreases (0.334, 0.276, and 0.247 Å, respectively). Finally, the best indicator of relative electronic activation is the HOMO-LUMO gap, as measured by the longest wavelength absorptions in the respective UV spectra.…”

“…This simple analysis has been quantified by DFT calculations for the parent frames. 11 A tentative indication of decreased antiaromaticity in the latter is found in the relative deshielding of H11 (δ = 6.91, CDCl 3 ) compared to H7 in 4 (δ = 6.43, CDCl 3 ), the choice of these hydrogens predicated on their unencumbrance by differences in their local environment. Further corroboration of this notion was sought by X-ray analysis, an initiative also stimulated by the dearth of such data for similar phenylenes.…”

Local aromaticity and aromatic sextet theory beyond Clar

“…In view that this contribution has been dedicated to Professor Ivan Gutman of the University of Kragujevac, who himself made numerous theoretical contributions to chemistry of benzenoid and nonbenzenoid hydrocarbons and aromaticity over his 50 years of scientific research, we end this paper by listing a selection of Gutman's relatively recent papers related to aromaticity . We selected papers published in 2009–2011, during which Gutman published some 100 papers, about 30 of which relate to benzenoid hydrocarbons and aromaticity, the other 70 covering other topics of mathematical chemistry.…”

Cyclic conjugation in benzo- and benzocyclobutadieno-annelated terrylenes and higher rylenes

“…The effect of such an annelation was also studied in due detail. [18][19][20][21][22][23] In many cases, but not all, 22,23 the following regularities could be envisaged:…”