Original scientific paper

https://doi.org/10.5562/cca3786

Postscript on Viable Ground-States for Calculating Topological π-Electron Ring-Currents Using the Hückel–London–Pople–McWeeny Model

Timothy. K. Dickens orcid.org/0000-0003-0342-3597 ; Peterhouse, Cambridge CB2 1RD, England, United Kingdom
Roger. B. Mallion orcid.org/0000-0002-3642-269X ; Peterhouse, Cambridge CB2 1RD, England, United Kingdom

Abstract

Attention is drawn to the idea that, in the context of the Hückel–London–Pople–McWeeny (HLPM) approach to π-electron ring-currents, the basic Aufbau process can be mimicked by means of a graph-theoretical algorithm and that the outcome is determined solely by the order of the eigenvalues of the arbitrary molecular-graph representing an extant or hypothetical conjugated system. The Aufbau process usually results in a closed-shell ground-state, but sometimes a unique triplet ground-state arises, sometimes doublets, as well as unique ground-states of higher multiplicity, are encountered, and, on occasions, no uniquely defined π-electronic ground-state is established at all. Previously, the only examples of the latter (‘pathological’) case — which, as with triplet ground-states and other ground-states that are not singlets, precludes the possibility of any HLPM calculation — were graphs that are unlikely candidates for being extant or viable conjugated systems. In this note, however, an example is documented of what is, ostensibly, a plausible unsaturated structure — namely, (Coronene)6–. In the conclusion, attention is drawn to a procedure that averages electron occupation amongst the several orbitals of a degenerate shell.

This work is licensed under a Creative Commons Attribution 4.0 International License.

Keywords

topological ring-currents in conjugated systems; π-electron triplet ground-states; Aufbau principle; ambiguous ground-states

Hrčak ID:

260959

URI

https://hrcak.srce.hr/260959

Publication date:

25.4.2021.

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