This are just a few insights I have got from some of the talks I attended. As usual, this does not represent a report on the WATOC congress itself, but simply some aspects that caught my personal eye. Read the rest of this entry »
WATOC25 and its (Dr Who like) regeneration to Young WATOC25.
June 21st, 2025The WATOC congresses occur every three years. WATOC25, the 13th in a series which started in 1987 takes places tomorrow in Oslo, Norway, The day before the main event there is something new – a session just for early career researchers or “Young WATOC”. As an “old” WATOCer, I dropped into the opening session and was delighted to find a packed auditorium, with literally standing room only comprising mostly young researchers in their 20s.
Mechanism of the dimerisation of Nitrosobenzene.
June 14th, 2025I am in the process of revising my annual lecture to first year university students on the topic of “curly arrows”. I like to start my story in 1924, when Robert Robinson published the very first example[cite]gg9g[/cite] as an illustration of why nitrosobenzene undergoes electrophilic bromination in the para position of the benzene ring. I follow this up by showing how “data mining” can be used to see if this supports his assertion. I have used the very latest version of the CSD crystal structure database to update the version originally posted here in 2020.[cite]10.59350/c6thp-wqe69[/cite]
How many of the compounds that appear in the chemical literature are mentioned just once?
June 6th, 2025Tom recently emailed me this question: Do you know how to find out how many of the compounds that appear in the chemical literature are mentioned just once? Intrigued, I first set out to find out how many substances, as Chemical Abstracts refers to the them, there were as of 5 June, 2025. There is a static estimate here (219 million), but to get the most up to date information, I asked CAS directly. They responded immediately (thanks Lee!) with 294,778,693 on the date mentioned above. It is not actually possible to answer the first question itself using CAS SciFinder, but again CAS came up with a value: “there are 113,383,649 substances in CAS Registry with only one CAplus citation” equivalent to “38.5% of the current substances have only 1 reference.” I should add this estimate was qualified by “that can be misleading, since that includes salts, multicomponents, etc. But that’s a first pass.” I am actually impressed that as many as 61.5% are mentioned more than once, since before learning the answer, I had intuitively guessed that percentage as being much lower.
Cyclo-S6 (Hexathiane) – anomeric effects again!
June 1st, 2025I 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.
Forty (one) years on – The pico-mac-nano and Chemdraw.
June 1st, 2025Last year I reminisced on the occasion of the 40th Anniversary of the Macintosh computer.[cite]10.59350/f11dr-93t29[/cite] Four decades of advances in technology now mean I can do a fair amount of computational quantum modelling on a recent Mac (one from 2022 with M1 processor), and since then they have only got even (~2 or 3 times) faster with the M4 processor. Many of the recent calculations done for these blogs have included at least one or two that were done on the Mac. So I was intrigued to find that a real working version of the original Mac is about to be released for sale, but with a twist. Its called the “Pico-mac-nano” and from its name it is truly diminutive, being only 6.2 cm high – half the height of a can of cola – and with a 2″ LCD display. It comes with a connector for a keyboard and mouse, although currently it has no sound.
S7I1+: The largest anomeric effect exhibited by sulfur.
May 21st, 2025In this series of posts about the electronic effects in small sulfur rings[cite]10.59350/rzepa.28615[/cite] I have explored increasingly large induced geometric effects. Here is the largest so far, for the compound S7I1+[cite]10.1021/ic50225a048[/cite]
5-Imino-5λ4-heptathiepane 3-oxide. More exuberent anomeric effects.
May 20th, 2025The two previous posts[cite]10.59350/rzepa.28515[/cite],[cite]10.59350/rzepa.28407[/cite] 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.
Cycloheptasulfur sulfoxide, S7O – Anomeric effects galore!
May 19th, 2025The monosulfoxide of cyclo-heptasulfur was reported along with cycloheptasulfur itself in 1977,[cite]10.1002/anie.197707161[/cite] 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.[cite]10.59350/rzepa.28407[/cite]
Cyclo-Heptasulfur, S7 – a classic anomeric effect discovered during a pub lunch!
May 16th, 2025Way back in 1977, the crystal structure of the sulfur ring S7 was reported.[cite]10.1002/anie.197707151[/cite] 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[cite]10.14469/hpc/15228[/cite] 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?