Posts Tagged ‘helical systems’

Linking numbers, and twist and writhe components for two extended porphyrins.

Sunday, February 17th, 2013

My last comment as appended to the previous post promised to analyse two so-called extended porphyrins for their topological descriptors. I start with the Cãlugãreanu/Fuller theorem  which decomposes the topology of a space curve into two components, its twist (Tw) and its writhe (Wr, this latter being the extent to which coiling of the central curve has relieved local twisting) and establishes a topological invariant called the linking number[1]

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References

  1. S.M. Rappaport, and H.S. Rzepa, "Intrinsically Chiral Aromaticity. Rules Incorporating Linking Number, Twist, and Writhe for Higher-Twist Möbius Annulenes", J. Am. Chem. Soc., vol. 130, pp. 7613-7619, 2008. http://dx.doi.org/10.1021/ja710438j

Anapolar ring currents: a [144]-Annulene.

Friday, February 1st, 2013

This is a recently published[1] (hypothetical) molecule which has such unusual properties that I cannot resist sharing it with you. It is an annulene with 144 all-cis CH groups, being a (very) much larger cousin of (also hypothetical) systems mooted in 2009[2],[3].

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References

  1. R.J.F. Berger, "Prediction of a Cyclic Helical Oligoacetylene Showing Anapolar Ring Currents in the Magnetic Field", Zeitschrift für Naturforschung B, vol. 67b, pp. 1127-1131, 2012. http://dx.doi.org/10.5560/ZNB.2012-0189
  2. S.M. Rappaport, and H.S. Rzepa, "Intrinsically Chiral Aromaticity. Rules Incorporating Linking Number, Twist, and Writhe for Higher-Twist Möbius Annulenes", J. Am. Chem. Soc., vol. 130, pp. 7613-7619, 2008. http://dx.doi.org/10.1021/ja710438j
  3. C.S. Wannere, H.S. Rzepa, B.C. Rinderspacher, A. Paul, C.S.M. Allan, H.F. Schaefer, and P.V.R. Schleyer, " The Geometry and Electronic Topology of Higher-Order Charged Möbius Annulenes † ", J. Phys. Chem. A, vol. 113, pp. 11619-11629, 2009. http://dx.doi.org/10.1021/jp902176a