Archive for the ‘Interesting chemistry’ Category
Wednesday, August 13th, 2025
In the previous post,[1] I introduced the N=N double bond in nitrosobenzene dimer, arguing that even though it was a formal double bond, its bond dissociation energy made it nonetheless a very weak double bond! This was backed up by a technique known as energy decomposition analysis or EDA. Here I use a variant of this method known as NEDA to look at some other strained alkenes, including the famously non-existent tetra t-Butyl ethene.
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References
- H. Rzepa, "The mysterious N=N double bond in nitrosobenzene dimer.", 2025. https://doi.org/10.59350/rzepa.29383
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Sunday, June 1st, 2025
I thought I was done with exploring anomeric effects in small sulfur rings. However, I then realised that all the systems that I had described had an odd number of atoms and that I had not looked at any even numbered rings. Thus hexasulfur is a smaller (known) ring version of S8, the latter by far the best known allotrope of this element of course.
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Wednesday, May 21st, 2025
In this series of posts about the electronic effects in small sulfur rings[1] I have explored increasingly large induced geometric effects. Here is the largest so far, for the compound S7I1+[2]
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References
- H. Rzepa, "5-Imino-5λ<sup>4</sup>-heptathiepane 3-oxide. More exuberent anomeric effects.", 2025. https://doi.org/10.59350/rzepa.28615
- J. Passmore, G. Sutherland, P. Taylor, T.K. Whidden, and P.S. White, "Preparations and x-ray crystal structures of iodo-cyclo-heptasulfur hexafluoroantimonate(V) and hexafluoroarsenate(V), S7ISbF6 and S7IAsF6", Inorganic Chemistry, vol. 20, pp. 3839-3845, 1981. https://doi.org/10.1021/ic50225a048
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Tuesday, May 20th, 2025
The two previous posts[1],[2] on the topic of anomeric effects in 7-membered sulfur rings illustrated how orbital interactions between the lone pairs in the molecules and S-S bonds produced widely varying S-S bond lengths in the molecules, some are shorter than normal (which is ~2.05Å for e.g. the S8 ring) by ~ 0.1Å and some are longer by ~0.24Å. Here we extend this to the unknown molecule shown below.
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References
- H. Rzepa, "Cycloheptasulfur sulfoxide, S<sub>7</sub>O – Anomeric effects galore!", 2025. https://doi.org/10.59350/rzepa.28515
- H. Rzepa, "Cyclo-Heptasulfur, S<sub>7</sub> – a classic anomeric effect discovered during a pub lunch!", 2025. https://doi.org/10.59350/rzepa.28407
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Monday, May 19th, 2025
The monosulfoxide of cyclo-heptasulfur was reported along with cycloheptasulfur itself in 1977,[1] along with the remarks that “The δ modification of S7 contains bonds of widely differing length: this has never been observed before in an unsubstituted molecule. and “the same effect having also been observed in other sulfur rings (S8O, S7I1+ and S7O).” Here I take a look at the last of these other molecules, the monosulfoxide of S7, as a follow up to the commentary on S7 itself.[2]
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References
- R. Steudel, R. Reinhardt, and T. Sandow, "Bond Interaction in Sulfur Rings: Crystal and Molecular Structure of <i>cyclo</i>‐Heptasulfur Oxide, S<sub>7</sub>O", Angewandte Chemie International Edition in English, vol. 16, pp. 716-716, 1977. https://doi.org/10.1002/anie.197707161
- H. Rzepa, "Cyclo-Heptasulfur, S<sub>7</sub> – a classic anomeric effect discovered during a pub lunch!", 2025. https://doi.org/10.59350/rzepa.28407
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Friday, May 16th, 2025
Way back in 1977, the crystal structure of the sulfur ring S7 was reported.[1] The authors noted that “The δ modification of S7 contains bonds of widely differing length: this has never been observed before in an unsubstituted molecule.” No explanation was offered, although they note that similar effects have been observed in S8O, S7I+ and S7O. The S7 molecule was yesterday brought to my attention (thanks Derek!) over a pub lunch and in the time honoured manner of scientists, sketched out on a napkin – with a pen obtained from the waitress!. As an “organic chemist”, I immediately thought “anomeric effects”. And so indeed it has proven. A calculation using the MN15L/Def2-TZVPP DFT method and analysis using the Weinhold NBO7 procedure[2] reveals the following structure (with Cs symmetry) and indeed the four unique S-S distances are all different (experimental values in parentheses). So how does this arise?
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References
- R. Steudel, R. Reinhardt, and F. Schuster, "Crystal and Molecular Structure of <i>cyclo</i>‐Heptasulfur (δ‐S<sub>7</sub>)", Angewandte Chemie International Edition in English, vol. 16, pp. 715-715, 1977. https://doi.org/10.1002/anie.197707151
- H. Rzepa, "Cyclo-Heptasulfur, S7 – a classic anomeric effect discovered during a pub lunch!", 2025. https://doi.org/10.14469/hpc/15228
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Saturday, February 1st, 2025
Derek Lowe tells the story of “carbyne”, a potential further allotrope of carbon, comprising linear chains of carbon atoms, C-C≡C-C≡C-C. Whether such a molecule can exist on its own has long been the the topic of speculation. Now a report has appeared of a “pseudocarbyne”, stabilised by gold atoms.[1]
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References
- J. Wu, P. Tarakeshwar, S.G. Sayres, M. Meneghetti, H. Kim, J. Barreto, and P.R. Buseck, "Crystal structure of Au-pseudocarbyne(C6)", Scientific Reports, vol. 15, 2025. https://doi.org/10.1038/s41598-024-80359-5
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Saturday, January 25th, 2025
This is another in the C&E News list of candidates for the Molecule of the Year, Molecular shuttle in a box [1] (more…)
References
- S. Ibáñez, P. Salvà, L.N. Dawe, and E. Peris, "Guest‐Shuttling in a Nanosized Metallobox", Angewandte Chemie International Edition, vol. 63, 2024. https://doi.org/10.1002/anie.202318829
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Wednesday, January 8th, 2025
Each year C&E News publishes a list of candidates for the Molecule of the Year. For 2024 the list is (in order of votes cast for each) (more…)
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