Croatica Chemica Acta, Vol. 87 No. 3, 2014.
Original scientific paper
https://doi.org/10.5562/cca2397
Ring-Current Assessment of the Annulene-Within-an-Annulene Model for some Large Coupled Super-Ring Conjugated-Systems
Timothy K. Dickens
; University Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, England, United Kingdom
Roger B. Mallion
; School of Physical Sciences, University of Kent, Canterbury CT2 7NH, England, United Kingdom
Abstract
The Annulene-Within-an-Annulene (AWA) model for conjugated super-ring systems, proposed by Barth and Lawton nearly fifty years ago, is further tested on six newly considered ‘coupled’ structures by means of π-electron ring-currents and bond-currents calculated via the Hückel–London–Pople–McWeeny (HLPM) formalism. Super-ring systems are said to be decoupled when the bonds connecting the central ring to the outer perimeter never appear as anything other than single bonds in any Kekulé structure that can be devised for the system as a whole. The preliminary conclusions of other recent inves¬tigations — by the same HLPM method and by ipso-centric ab-initio approaches — are verified. Phenyl-ene-[5]-circulene, a (coupled) alternant isomer of the much-studied (decoupled) non-alternant system [10,5]-coronene, is also considered. It is advised that the AWA model should in future either be used with consider¬able caution in very specific circumstances, or it should be abandoned altogether.
Keywords
HLPM ring-currents & bond-currents; graph theory; conjugated hydrocarbons; coupled & decoupled super-ring systems; annulene-within-an-annulene rule
Hrčak ID:
130429
URI
Publication date:
18.11.2014.
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