Archive for the ‘Interesting chemistry’ Category

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 )6 2+ ", 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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George Olah and the norbornyl cation.

Friday, March 10th, 2017
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George Olah passed away on March 8th. He was part of the generation of scientists in the post-war 1950s who had access to chemical instrumentation that truly revolutionised chemistry. In particular he showed how the then newly available NMR spectroscopy illuminated structures of cations in solvents such “Magic acid“. The obituaries will probably mention his famous “feud” with H. C. Brown over the structure of the norbornyl cation (X=CH2+), implicated in the mechanism of many a solvolysis reaction that characterised the golden period of physical organic chemistry just before and after WWII. 

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More tetrahedral fun. Spherical aromaticity (and other oddities) in N4 and C4 systems?

Thursday, March 2nd, 2017
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The thread thus far. The post about Na2He introduced the electride anionic counter-ion to Na+ as corresponding topologically to a rare feature known as a non-nuclear attractor. This prompted speculation about other systems with such a feature, and the focus shifted to a tetrahedral arrangement of four hydrogen atoms as a dication, sharing a total of two valence electrons. The story now continues here.

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The H4 (2+) dication and its bonding.

Wednesday, February 15th, 2017
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This post arose from a comment attached to the post on Na2He and relating to peculiar and rare topological features of the electron density in molecules called non-nuclear attractors. This set me thinking about other molecules that might exhibit this and one of these is shown below.

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VSEPR Theory: A closer look at bromine trifluoride, BrF3.

Tuesday, February 14th, 2017
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I analysed the bonding in chlorine trifluoride a few years back in terms of VSEPR theory. I noticed that several searches on this topic which led people to this post also included a query about the differences between it and the bromine analogue. For those who posed this question, here is an equivalent analysis.

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Na2He: a stable compound of helium and sodium at high pressure.

Saturday, February 11th, 2017
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On February 6th I was alerted to this intriguing article[1] by a phone call, made 55 minutes before the article embargo was due to be released. Gizmodo wanted to know if I could provide an (almost) instant quote. After a few days, this report of a stable compound of helium and sodium still seems impressive to me and I now impart a few more thoughts here.

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References

  1. X. Dong, A.R. Oganov, A.F. Goncharov, E. Stavrou, S. Lobanov, G. Saleh, G. Qian, Q. Zhu, C. Gatti, V.L. Deringer, R. Dronskowski, X. Zhou, V.B. Prakapenka, Z. Konôpková, I.A. Popov, A.I. Boldyrev, and H. Wang, "A stable compound of helium and sodium at high pressure", Nature Chemistry, 2017. http://dx.doi.org/10.1038/nchem.2716

Forming a stabilized m-benzyne.

Friday, January 20th, 2017
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The story so far. Inspired by the report of the most polar neutral compound yet made, I suggested some candidates based on the azulene ring system that if made might be even more polar. This then led to considering a smaller π-analogue of azulene, m-benzyne. Here I ponder how a derivative of this molecule might be made, using computational profiling as one reality check.

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Braiding a molecular knot with eight crossings.

Friday, January 20th, 2017
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This is one of those posts of a molecule whose very structure is interesting enough to merit a picture and a 3D model. The study[1] reports a molecular knot with the remarkable number of eight crossings.

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References

  1. J.J. Danon, A. Krüger, D.A. Leigh, J. Lemonnier, A.J. Stephens, I.J. Vitorica-Yrezabal, and S.L. Woltering, "Braiding a molecular knot with eight crossings", Science, vol. 355, pp. 159-162, 2017. http://dx.doi.org/10.1126/science.aal1619