Archive for the ‘Interesting chemistry’ Category

The Bond Slam – a second peek inside.

Saturday, August 12th, 2017
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At the moment, the bond slam is something of a home from home for this blog and since much of my activity is happening there rather than here, I thought I might give you pointers to some of the topics, which are evolving, so to speak, before our very eyes.

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Chemical Bonds at the 21st Century – 2017: the Bond Slam.

Wednesday, August 2nd, 2017
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It is always interesting to observe conference experiments taking place. The traditional model involves travelling to a remote venue, staying in a hotel, selecting sessions to attend from a palette of parallel streams and then interweaving chatting to colleagues both old and new over coffee, lunch, dinner or excursions. Sometimes conferences occur in clusters, with satellite meetings breaking out in the vicinity, after a main conference has done the job of attracting delegates to the region. Here I bring to your attention one such experiment, the Bond Slam which is part of a satellite meeting in Aachen to be held September 2-4 2017 on the topic of Chemical Bonds at the 21st Century, following on from the WATOC 2017 congress in Munich Germany a few days earlier.

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Dispersion “bonds” not involving just hydrogen: can it work for F…H?

Tuesday, July 18th, 2017
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The effects of loading up lots of dispersion attractions (between t-butyl groups) into a compact molecule has the interesting consequence of allowing two “non-bonded” hydrogen atoms to approach to ~1.5Å of each other, thus creating the appearance of a “bond” where one normally would not be found. Can such an effect be injected into other combinations of two atoms, say H and F? Here I briefly explore this notion.

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Dispersion “bonds”: a new example with an ultra-short H…H distance.

Monday, June 26th, 2017
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About 18 months ago, there was much discussion on this blog about a system reported by Bob Pascal and co-workers containing a short H…H contact of ~1.5Å[1]. In this system, the hydrogens were both attached to Si as Si-H…H-Si and compressed together by rings. Now a new report[2] and commented upon by Steve Bachrach, claims a similar distance for hydrogens attached to carbon, i.e. C-H…H-C, but without the ring compression.

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References

  1. J. Zong, J.T. Mague, and R.A. Pascal, "Exceptional Steric Congestion in anin,in-Bis(hydrosilane)", Journal of the American Chemical Society, vol. 135, pp. 13235-13237, 2013. http://dx.doi.org/10.1021/ja407398w
  2. S. Rösel, H. Quanz, C. Logemann, J. Becker, E. Mossou, L. Cañadillas-Delgado, E. Caldeweyher, S. Grimme, and P.R. Schreiner, "London Dispersion Enables the Shortest Intermolecular Hydrocarbon H···H Contact", Journal of the American Chemical Society, vol. 139, pp. 7428-7431, 2017. http://dx.doi.org/10.1021/jacs.7b01879

Cyclopropenium cyclopentadienide: a strangely neutral ion-pair?

Sunday, April 9th, 2017
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Both the cyclopropenium cation and the cyclopentadienide anion are well-known 4n+2-type aromatic ions, but could the two together form an ion-pair?

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What is the (calculated) structure of a norbornyl cation anion-pair in water?

Saturday, April 1st, 2017
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In a comment appended to an earlier post, I mused about the magnitude of the force constant relating to the interconversion between a classical and a non-classical structure for the norbornyl cation. Most calculations indicate the force constant for an “isolated” symmetrical cation is +ve, which means it is a true minimum and not a transition state for a [1,2] shift. The latter would have been required if the species equilibrated between two classical carbocations. I then pondered what might happen to both the magnitude and the sign of this force constant if various layers of solvation and eventually a counter-ion were to be applied to the molecule, so that a bridge of sorts between the different states of solid crystals, superacid and aqueous solutions might be built.

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MOLinsight: A web portal for the processing of molecular structures by blind students.

Friday, March 31st, 2017
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Occasionally one comes across a web site that manages to combine being unusual, interesting and also useful. Thus www.molinsight.net is I think a unique chemistry resource for blind and visually impaired students.

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First, hexacoordinate carbon – now pentacoordinate nitrogen?

Saturday, March 25th, 2017
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A few years back I followed a train of thought here which ended with hexacoordinate carbon, then a hypothesis rather than a demonstrated reality. That reality was recently confirmed via a crystal structure, DOI:10.5517/CCDC.CSD.CC1M71QM[1]. Here is a similar proposal for penta-coordinate nitrogen.

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References

  1. M. Malischewski, and K. Seppelt, "Crystal Structure Determination of the Pentagonal-Pyramidal Hexamethylbenzene Dication C6(CH3)62+", Angewandte Chemie International Edition, vol. 56, pp. 368-370, 2016. http://dx.doi.org/10.1002/anie.201608795

Peroxydisulfate – “enables a non-enzymatic Krebs cycle precursor”

Sunday, March 19th, 2017
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The Wikipedia entry on peroxydisulfate is quite short (as of today). But I suspect this article may change things.[1].

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References

  1. M.A. Keller, D. Kampjut, S.A. Harrison, and M. Ralser, "Sulfate radicals enable a non-enzymatic Krebs cycle precursor", Nature Ecology & Evolution, vol. 1, pp. 0083, 2017. http://dx.doi.org/10.1038/s41559-017-0083

Expanding on the curious connection between the norbornyl cation and small-ring aromatics.

Sunday, March 12th, 2017
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This is another of those posts that has morphed from an earlier one noting the death of the great chemist George Olah. The discussion about the norbornyl cation concentrated on whether this species existed in a single minimum symmetric energy well (the non-classical Winstein/Olah proposal) or a double minimum well connected by a symmetric transition state (the classical Brown proposal). In a comment on the post, I added other examples in chemistry of single/double minima, mapped here to non-classical/classical structures. I now expand on the examples related to small aromatic or anti-aromatic rings.

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