Counter-Rotating Ring Currents in Coronene and Corannulene

Abstract

Explicit ab initio current‐density maps contradict the annulene‐within‐an‐annulene model of [n]circulenes: in both coronene and corannulene the expected diamagnetic current on the perimeter is opposed by the central, paramagnetic ring current (see schematic representation).

Comparisons of π-Electron Ring-Current and Bond-Current Patterns Calculated by Topological (‘HLPM’) and Ab Initio (‘Ipso-Centric’) Formalisms for Two Isomeric Conjugated Hydrocarbons, Corazulene and Cornaphthalene

“…According to common belief, such predictive success should ostensibly be the preserve only of sophisticated, and much less intuitive, [47,48] ab initio calculations. This conclusion is entirely consistent with our own previous findings [21,22] and with the view expressed in the recent, independent and simultaneous work of Gershoni-Poranne et al on phenylenes, [34] that the relative currents calculated by the (equivalent of the) HLPM topological approach '...are remarkably similar to those extracted from the pseudo-π maps, [8] which themselves mirror the full ab initio maps [7,11,15,19,20,49] '…and that, in general, the HLPM topological method '...has a remarkable ability…to capture essential features of delocalised systems including patterns of current…' There is therefore now a growing body of evidence [17,21,22,32−37] that this is the case. [6,28,29] ring-currents (in black) and the associated topological [6,28,29] bond-currents (in red) for (alternant [2] ) cornaphthalene (2).…”

Efficient mapping of ring currents in fullerenes and other curved carbon networks

“…Given their paratropic pentagonal ring currents, neither C 60 nor C 70 should be considered as especially aromatic on the magnetic criterion. The paratropicity of the pentagons in C 60 and C 70 is consistent with the diatropic-rim, paratropic-hub pattern of current found in bowl-shaped corannulene [55], which is itself part of a more general pattern in which the central ring of an [n]circulene is paratropic and the perimeter diatropic [56].…”

Multidimensionality of delocalization indices and nucleus‐independent chemical shifts in polycyclic aromatic hydrocarbons II: Proof of further nonlocality

“…The MCBI were computed using the in home developed Kekule program which uses the Gaussian-03 [31] formatted checkpoint file. The NICSzz [10,32] were also calculated in the Pseudo-π approach [1] using Gaussian-03. For the study of correlations between the NICS and multicenter indices, the ARTE-QSAR program was used [33] .…”

“…Although originally well defined in terms of similarity between benzenoid rings [2] , over time it has been used for many different classes of molecules, making it a fuzzy concept. The lack of an immediate observable has resulted in a multiplicity of indices to quantify aromaticity, based on energetic [3] , geometric [4] , quantum chemical [5] or magnetic considerations [6][7][8][9][10] . A concept closely related to aromaticity is that of electron delocalization, of which the Multi Centre Bond Index (MCBI), recently introduced by our group [11][12][13][14] , has been shown to be a successful measure [15] .…”