Henry Rzepa's Blog Chemistry with a twist

February 17, 2013

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

Filed under: Interesting chemistry — Tags: , — Henry Rzepa @ 9:30 am

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", Journal of the American Chemical Society, vol. 130, pp. 7613-7619, 2008. http://dx.doi.org/10.1021/ja710438j

February 1, 2013

Anapolar ring currents: a [144]-Annulene.

Filed under: Interesting chemistry — Tags: , — Henry Rzepa @ 8:37 pm

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. 67, 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", Journal of the American Chemical Society, 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", The Journal of Physical Chemistry A, vol. 113, pp. 11619-11629, 2009. http://dx.doi.org/10.1021/jp902176a

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