Posts Tagged ‘Nature’

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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Stable “unstable” molecules: a crystallographic survey of cyclobutadienes and cyclo-octatetraenes.

Sunday, March 5th, 2017
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Cyclobutadiene is one of those small iconic molecules, the transience and instability of which was explained theoretically long before it was actually detected in 1965.[1] Given that instability, I was intrigued as to how many crystal structures might have been reported for this ring system, along with the rather more stable congener cyclo-octatetraene. Here is what I found.

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References

  1. L. Watts, J.D. Fitzpatrick, and R. Pettit, "Cyclobutadiene", Journal of the American Chemical Society, vol. 87, pp. 3253-3254, 1965. http://dx.doi.org/10.1021/ja01092a049

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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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

The “hydrogen bond”; its early history.

Saturday, December 31st, 2016
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My holiday reading has been Derek Lowe’s excellent Chemistry Book setting out 250 milestones in chemistry, organised by year. An entry for 1920 entitled hydrogen bonding seemed worth exploring in more detail here.

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The dipole moments of highly polar molecules: glycine zwitterion.

Saturday, December 24th, 2016
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The previous posts produced discussion about the dipole moments of highly polar molecules. Here to produce some reference points for further discussion I look at the dipole moment of glycine, the classic zwitterion (an internal ion-pair).

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Molecules of the year? Pnictogen chains and 16 coordinate Cs.

Monday, December 19th, 2016
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I am completing my survey of the vote for molecule of the year candidates, which this year seems focused on chemical records of one type or another.

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Long C=C bonds.

Thursday, December 1st, 2016
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Following on from a search for long C-C bonds, here is the same repeated for C=C double bonds.

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Molecule orbitals as indicators of reactivity: bromoallene.

Thursday, September 1st, 2016
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Bromoallene is a pretty simple molecule, with two non-equivalent double bonds. How might it react with an electrophile, say dimethyldioxirane (DMDO) to form an epoxide?[1] Here I explore the difference between two different and very simple approaches to predicting its reactivity. bromoallene

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References

  1. D. Christopher Braddock, A. Mahtey, H.S. Rzepa, and A.J.P. White, "Stable bromoallene oxides", Chem. Commun., vol. 52, pp. 11219-11222, 2016. http://dx.doi.org/10.1039/C6CC06395K