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

Abstract

Abstract:The π-electron ring-currents and bond-currents associated with the isomeric structures corazulene (1) and cornaphthalene (2) are calculated by means of the rudimentary topological Hückel-London-Pople-McWeeny (HLPM) method (which is entirely equivalent to the recently named 'graph-theoretical CD-HL' approach).These currents are compared with analogous quantities computed by Lillington et al. by use of the more-sophisticated ipso-centric ab initio approach. The simple HLPM method is seen to exhibit a remarkable ability to reproduce complex patterns of current in large polycyclic hydrocarbons -the successful prediction of which, ostensibly, might naïvely be expected to be the preserve only of more sophisticated, and much less intuitive, ab initio calculations. This conclusion is entirely consistent with findings from contemporary work on other structures by the present, and other, authors.

Ring-Current Properties of Bispentalenes and Related Structures — Comparison of Ab Initio and Hückel-London-Pople-McWeeny (HLPM) ‘Topological’ Calculations

“…[7][8][9][10][11][12][13][14][15][16][17][18][19]) are routinely available, however, this consideration is, of course, no longer so relevant. That is why, in the current work, and earlier but recent ones, [27][28][29][30][31][32][33] the above reservation about non-iterative calculations expressed in Refs. [47,[61][62][63][64][65] have been temporarily set aside in order to test how well the predictions of the ab initio methods compare with even the most basic, non-iterative pseudograph-theoretical version of the Hückel-London-PopleMcWeeny approach; [1][2][3][4][5][6] in this formalism, the calculated quantities (ring currents and bond currents) are effectively regarded -despite the cautions and caveats considered by one of us (RBM) in Ref.…”

Magnetic Aromaticity of Cycloporphyrin Nanorings

“…To this end, it is customary to take the benzene C-C current strength as the reference and to compare the relative current strength. This procedure allows the comparison of the results coming from very different methods, even non-ab initio [47]. Absolute current strengths require extending the integration domain toward the onset of a circulation close to a different bond.…”

Calculated Magnetic Properties of a Recently Synthesized Corannulene–Dibenzobistetracene Hybrid

“…We have previously argued that the conceptually simple and pictorially appealing HLPM topological method has demonstrated “... a possibly unexpected ability to reproduce complex patterns of current in large polycyclic hydrocarbons.” Furthermore, as, for example, Gershoni-Poranne et al have observed, the HLPM topological method “... has a remarkable ability ... to capture essential features of delocalized systems including patterns of current ...” that frequently mimic the predictions of more sophisticated, but less immediately intuitive, ab initio approaches. Irons et al have recently observed that the agreement between the HLPM method and several ab initio formalisms, including their own, “... suggests that for planar systems ring currents are consistently described and well interpreted by simple approaches such as HLPM.” We now add the discussion on Corannulene–DBT that has been developed in the present Note to the growing body of evidence that this is also the case for certain geometrically nonplanar conjugated species.…”

“…Our attention was attracted to these NICS calculations reported by Xu et al on this extensive 24-ring unsaturated structure because we have for some time been taking opportunities, when they arise, for example, in refs − , to compare ab initio calculations of the magnetic properties of various conjugated systems with predictions of the rudimentary, quasi graph-theoretical Hückel–London–Pople–McWeeny (HLPM) method of calculating π-electron ring currents. This approach is reviewed in detail in ref Such comparisons have been made previously in, for example, refs − .…”