Archive for the ‘Interesting chemistry’ Category

Non-covalent-interaction (NCI) surfaces for two large annulenes (revisited).

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

  1. 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

The chemical synthesis of C2: another fascinating twist to the story.

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

  1. 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
  2. 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

The thermal reactions … took precisely the opposite stereochemical course to that which we had predicted

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

  1. 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

Dispersion attraction effects on the computed geometry of a leminscular dodecaporphyrin.

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

  1. 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

Global aromaticity at the nanoscale.

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

  1. 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

Tying different knots in a molecular strand.

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

  1. 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

An interesting aromatic molecule found in Titan’s atmosphere: cyclopropylidene.

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

  1. 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

A new example of a quadruple bond from carbon – to Fe.

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

  1. 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
  2. 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

Room-temperature superconductivity in a carbonaceous sulfur hydride!

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

  1. 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

High-performance polythioesters with high chemical recyclability.

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

  1. 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