Topological Ring-Currents in Some 'Super-Ring' Molecules
Presented by Dr. Roger MALLION
Type: Oral presentation
The Hückel–London–Pople–McWeeny (HLPM) (‘Topological’) approach1–4 for calculating π-electron ring-currents and bond-currents in conjugated systems is applied to a series of structures that have been called ‘super-ring’ molecules5. These consist of an outer ring of carbon atoms (of perimeter length either [4n] or [4n+2]) connected by internal C–C bonds to an inner, central ring, which is likewise of length either [4n] or [4n+2]. In none of the cases considered is the original ‘annulene-within-an-annulene’ (AWA) model6 respected. An alternative criterion is suggested — what we have named the ‘Ring-Current AWA’, based on ring currents rather than bond currents — whose provisions ostensibly have a greater probability of being fulfilled by any given structure. This new rule requires (a) that diamagnetic ring-currents should be manifested in all peripheral rings that form part of a [4n+2]-membered outer rim, as well as in any [4n+2]-membered inner-ring; and (b) that paramagnetic ring-currents should be evident in all peripheral rings that form part of a [4n]-membered outer-rim, as well as in any [4n]-membered inner-ring. This model is respected by almost all the examples studied here and elsewhere; however, a counter-example (-coronaphene]) is identified even to this more-restricted AWA rule. Accordingly, it is concluded that that neither form of the AWA rule can generally be regarded as reliable. 1. R. B. Mallion, Croat. Chem. Acta 2008, 81, 227–246. 2. A. T. Balaban, T. K. Dickens, I. Gutman & R. B. Mallion, Croat. Chem. Acta 2010, 83, 209–215. 3. T. K. Dickens & R. B. Mallion, J. Phys.Chem. A 2011, 115, 351–356. 4. T. K. Dickens & R. B. Mallion, J. Phys. Chem. A 2011, 115, 13877–13884. 5. J.-I. Aihara, J. Phys. Chem. A 2008, 112, 4382–4385. 6. E. Steiner, P. W. Fowler, L. W. Jenneskens & A. Acocella, Chem. Commun. 2001, pp. 659–660.
Location: Portorož, Slovenia
Address: University of Primorska, Faculty of Tourism Studies, Obala 11a, SI-6320 Portorož - Portorose, Slovenia
- Dr. Roger MALLION School of Physical Sciences, Universityof Kent, Canterbury CT2 7NH, England, United Kingdom