In the previous post,[cite]10.59350/rzepa.29383[/cite] 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.

In an earlier blog, I discussed[cite]10.59350/rzepa.28849[/cite] the curly arrows associated with the known dimerisation of nitrosobenzene, and how the N=N double bond (shown in red below) forms in a single concerted process. One of the properties of this molecule is that the equilibrium between the monomer and dimer can be detected[cite]10.1002/mrc.1260251118[/cite], with significant concentrations of the dimer observed below 10°C.

In the previous post[cite]10.59350/rzepa.28993[/cite] I followed up on an article published on the theme “ Physical Organic Chemistry: Never Out of Style “.[cite]10.1021/acs.joc.5c00426[/cite] Paul Rablen presented the case that the amount of o (ortho) product in electrophilic substitution of a phenyl ring bearing an EWG (electron withdrawing group) is often large enough to merit changing the long held rule-of-thumb for EWGs from

The title of this post comes from an article published in a special virtual issue on the theme “ Physical Organic Chemistry: Never Out of Style “[cite]10.1021/acs.joc.5c00426[/cite] There, Paul Rablen presents the case that the amount of o (ortho) product in electrophilic substitution of a phenyl ring bearing an EWG (electron withdrawing group) is often large enough to merit changing the long held rule-of-thumb for EWGs from

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. Frank Neese talked about his Bubblepole approximation for large molecules.[cite]10.1021/acs.jpca.4c07415[/cite] And he was not kidding – large.

The 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.

I 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]10.1002/jctb.5000435208[/cite] as an illustration of why nitrosobenzene undergoes electrophilic bromination in the para position of the benzene ring.

Tom 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.

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 S ₈ , the latter by far the best known allotrope of this element of course.

Last 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.

In 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 S ₇ I ¹⁺ [cite]10.1021/ic50225a048[/cite] The calculated geometry[cite]10.14469/hpc/15236[/cite] is shown below, with the crystallographic values in parentheses – the two matching very well.