Electron ring-currents and bond-currents in [10,5]-Coronene and related structures conforming to the Annulene-Within-an-Annulene model

• Main Authors: Dickens, T. K, Mallion, R. B
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c3cp00053b

A series of hypothetical conjugated structures is defined; the series is called the p -Coronenes and the first four members of it are shown to respect the Annulene-Within-an-Annulene (AWA) model when tested by means of HckelLondonPopleMcWeeny (HLPM) -electron ring-current and bond-current calculations. The first member of this series, 5-Coronene, is also a member of the regular [ r , s ]-Coronene series, where it is known as [10,5]-Coronene. It is shown that, as p is varied (with p always odd, and with p > 3) through the values 5, 7, 9, 11, etc. , the resulting structures alternate between a [4 n + 2]-Annulene-Within-a-[4 m ]-Annulene (if ( p 1) is divisible by 4) and a [4 n ]-Annulene-Within-a-[4 m + 2]-Annulene (if ( p 1) is not divisible by 4). It is therefore claimed that the p -Coronenes constitute an ideal series for testing the AWA model. It is also remarked that each member of the p -Coronene series has only four Kekul structures, and that the spokes or transverse bonds connecting the central [ p ( p 3)]-membered ring to the outer [ p ( p 1)]-membered periphery always have a Pauling bond-order of zero, ensuring that the outer and inner rings are decoupled; such bonds also bear zero bond-current, by symmetry. It is argued that the former property of these transverse bonds, rather than the latter, determines that the p -Coronenes obey the AWA rulewhich is in fact an exception, rather than a rule per se . The paper concludes by explicitly stating our philosophy that a conceptually simple model depending on no subjective (or any other) parameters whatsoever can give intuitive chemical insight for certain systems equal to that available from far-more complex methods such as ab initio calculationswhat Coulson once famously called primitive patterns of understanding. A series of hypothetical conjugated structures is defined; the series is called the p -Coronenes and the first four members of it are shown to respect the Annulene-Within-an-Annulene (AWA) model when tested by -electron ring-current and bond-current calculations.