Archive for the ‘Interesting chemistry’ Category
Sunday, February 7th, 2021
The last post addressed the concept of “steric clashes” in a pericyclic reaction transition state as an extension of the time honoured practice of building molecular models to analyse reaction outcomes. A modern computer generated model might express this in terms of a NCI (non-covalent-interaction) surface. A few posts ago, I had looked at some “molecules of the year” for 2020, one of which was a “figure-eight” twisted dodecaporphyrin in which an aspect of the reported[1] geometry had struck me as potentially lacking features due to the so-called non-covalent dispersion or van der Waals attractions. So I am revisiting here by adding the NCI surface for this molecule and one other.
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References
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M. Rickhaus, M. Jirasek, L. Tejerina, H. Gotfredsen, M.D. Peeks, R. Haver, H. Jiang, T.D.W. Claridge, and H.L. Anderson, "Global aromaticity at the nanoscale", Nature Chemistry, vol. 12, pp. 236-241, 2020. http://dx.doi.org/10.1038/s41557-019-0398-3
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Wednesday, January 20th, 2021
Last May, I wrote an update to the story sparked by the report of the chemical synthesis of C2.[1] This species has a long history of spectroscopic observation in the gas phase, resulting from its generation at high temperatures.[2] The chemical synthesis however was done in solution at ambient or low temperatures, a game-changer as they say. Here I give another update to this unfolding story.
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References
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K. Miyamoto, S. Narita, Y. Masumoto, T. Hashishin, T. Osawa, M. Kimura, M. Ochiai, and M. Uchiyama, "Room-temperature chemical synthesis of C2", Nature Communications, vol. 11, 2020. http://dx.doi.org/10.1038/s41467-020-16025-x
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T.W. Schmidt, "The Spectroscopy of C2: A Cosmic Beacon", Accounts of Chemical Research, vol. 54, pp. 481-489, 2021. http://dx.doi.org/10.1021/acs.accounts.0c00703
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Wednesday, January 20th, 2021
The quote of the post title comes from R. B. Woodward explaining the genesis of the discovery of what are now known as the Woodward-Hoffmann rules for pericyclic reactions.[1] I first wrote about this in 2012, noting that “for (that) blog, I do not want to investigate the transition states”. Here I take a closer look at this aspect.
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References
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R.B. Woodward, and R. Hoffmann, "Stereochemistry of Electrocyclic Reactions", Journal of the American Chemical Society, vol. 87, pp. 395-397, 1965. http://dx.doi.org/10.1021/ja01080a054
Posted in crystal_structure_mining, Historical, Interesting chemistry, pericyclic | No Comments »
Friday, January 1st, 2021
In the previous post, I showed the geometries of three large cyclic porphyrins, as part of an article[1] on exploring the aromaticity of large 4n+2 cyclic rings. One of them had been induced into a “figure-eight” or lemniscular conformation, as shown below.
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References
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M. Rickhaus, M. Jirasek, L. Tejerina, H. Gotfredsen, M.D. Peeks, R. Haver, H. Jiang, T.D.W. Claridge, and H.L. Anderson, "Global aromaticity at the nanoscale", Nature Chemistry, vol. 12, pp. 236-241, 2020. http://dx.doi.org/10.1038/s41557-019-0398-3
Posted in Interesting chemistry | No Comments »
Thursday, December 31st, 2020
Here is another of the “large” molecules in the c&e news shortlist for molecule-of-the-year, 2020. This one is testing the Hückel 4n+2 rule out to a value never before seen (n = 40, or 162 π-electrons).[1] The take-home message is that this rule seems to behave well in predicting global aromaticity even at this sort of scale!
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References
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M. Rickhaus, M. Jirasek, L. Tejerina, H. Gotfredsen, M.D. Peeks, R. Haver, H. Jiang, T.D.W. Claridge, and H.L. Anderson, "Global aromaticity at the nanoscale", Nature Chemistry, vol. 12, pp. 236-241, 2020. http://dx.doi.org/10.1038/s41557-019-0398-3
Posted in Interesting chemistry | No Comments »
Wednesday, December 30th, 2020
The title derives from an article[1] which was shortlisted for the annual c&en molecule of the year 2020 awards (and which I occasionally cover here). In fact this year’s overall theme is certainly large molecules, the one exception being a smaller molecule with a quadruple bond to boron, a theme I have already covered here.
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References
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D.A. Leigh, F. Schaufelberger, L. Pirvu, J.H. Stenlid, D.P. August, and J. Segard, "Tying different knots in a molecular strand", Nature, vol. 584, pp. 562-568, 2020. http://dx.doi.org/10.1038/s41586-020-2614-0
Posted in Interesting chemistry | No Comments »
Saturday, November 7th, 2020
Cyclopropylidene must be the smallest molecule to be aromatic due to π-electrons, with just three carbon atoms and two hydrogen atoms. It has now been detected in the atmosphere of Titan, one of Saturn’s moons[1] and joining benzene, another aromatic molecule and the protonated version C3H3+ there.
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References
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C.A. Nixon, A.E. Thelen, M.A. Cordiner, Z. Kisiel, S.B. Charnley, E.M. Molter, J. Serigano, P.G.J. Irwin, N.A. Teanby, and Y. Kuan, "Detection of Cyclopropenylidene on Titan with ALMA", The Astronomical Journal, vol. 160, pp. 205, 2020. http://dx.doi.org/10.3847/1538-3881/abb679
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Saturday, November 7th, 2020
Way back in 2010, I was writing about an experience I had just had during an organic chemistry tutorial, which morphed into speculation as to whether a carbon atom might sustain a quadruple bond to nitrogen. A decade on, and possibly approaching 100 articles by many authors on the topic, quadruple bonds to carbon continue to fascinate. Now an article as appeared[1] repeating this speculation for a carbon to iron quadruple bond,‡ in the very simple species C⩸Fe(CO)3 (see also a Rh-B equivalent.[2] This is particularly exciting because of the very real prospect of synthesising this species and perchance getting a crystal structure (something not possible with most of the other quadruply bonded carbon systems studied to date).
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References
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A.J. Kalita, S.S. Rohman, C. Kashyap, S.S. Ullah, and A.K. Guha, "Transition metal carbon quadruple bond: viability through single electron transmutation", Physical Chemistry Chemical Physics, vol. 22, pp. 24178-24180, 2020. http://dx.doi.org/10.1039/d0cp03436c
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L.F. Cheung, T. Chen, G.S. Kocheril, W. Chen, J. Czekner, and L. Wang, "Observation of Four-Fold Boron–Metal Bonds in RhB(BO–) and RhB", The Journal of Physical Chemistry Letters, vol. 11, pp. 659-663, 2020. http://dx.doi.org/10.1021/acs.jpclett.9b03484
Posted in Interesting chemistry | 1 Comment »
Saturday, October 17th, 2020
The title of this post indicates the exciting prospect that a method of producing a room temperature superconductor has finally been achived[1]. This is only possible at enormous pressures however; >267 gigaPascals (GPa) or 2,635,023 atmospheres.
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References
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E. Snider, N. Dasenbrock-Gammon, R. McBride, M. Debessai, H. Vindana, K. Vencatasamy, K.V. Lawler, A. Salamat, and R.P. Dias, "Room-temperature superconductivity in a carbonaceous sulfur hydride", Nature, vol. 586, pp. 373-377, 2020. http://dx.doi.org/10.1038/s41586-020-2801-z
Posted in Chemical IT, Interesting chemistry | No Comments »
Wednesday, September 2nd, 2020
Here I investigate a recent report[1] of a new generation of polyesters with the intrinsic properties of high crystallinity and chemical recyclability. The latter point is key, since many current plastics cannot be easily recycled to a form which can be used to regenerate the original polymer with high yield. Here I show some aspects of this fascinating new type of polymer.
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References
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C. Shi, M.L. McGraw, Z. Li, L. Cavallo, L. Falivene, and E.Y. Chen, "High-performance pan-tactic polythioesters with intrinsic crystallinity and chemical recyclability", Science Advances, vol. 6, pp. eabc0495, 2020. http://dx.doi.org/10.1126/sciadv.abc0495
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