The two previous surveys of the potential energy surface for this, it has to be said, rather obscure reaction led to energy barriers that were rather to high to be entirely convincing. So here is a third possibility. The red section corresponds to the previous exploration, in which a 3-membered sulfur ring intermediate was mooted. Here we go back to a 3-ring with nitrogen instead.

Continuing an exploration of the mechanism of this reaction, an alternative new mechanism was suggested in 1989 (having been first submitted to the journal ten years earlier!).[cite]10.1002/jhet.5570260518[/cite] Here the key intermediate proposed is a thiirenium cation (labelled 8 in the article) and labelled Int3 below.

Sometimes a (scientific) thought just pops into one’s mind. Most are probably best not shared with anyone, but since its the summer silly season, I thought I might with this one. Famously, according to Einstein, m  = E/c^^2, the equivalence of energy to mass. Consider a typical exoenergic chemical reaction:  A → B, ΔG -100 kJ/mol.

The Willgerodt reaction[cite]10.1002/cber.18870200278[/cite], discovered in 1887 and shown below, represents a transformation with a once famously obscure mechanism. A major step in the elucidation of that mechanism came[cite]10.1021/ja01157a034[/cite] using the then new technique of ¹⁴ C radio-labelling, shortly after the atom bomb projects during WWII made ¹⁴ CO ₂ readily available to researchers.

One of the most fascinating and important articles dealing with curly arrows I have seen is that by Klein and Knizia on the topic of C-H bond activations using an iron catalyst.[cite]10.1002/anie.201805511[/cite] These are so-called high spin systems with unpaired electrons and the mechanism of C-H activation involves both double headed (two electron) and fish-hook (single electron) movement.

Metaldehyde is an insecticide used to control slugs. When we unsuccessfully tried to get some recently, I discovered it is now deprecated in the UK. So my immediate reaction was to look up its structure to see if that cast any light (below, R=CH3, shown as one stereoisomer).

With the current global lockdown, and students along with everyone else staying at home, I have noticed some old posts of mine are getting more attention than normal.

My previous two posts on the topic of strongest bonds have involved mono and diprotonating N ₂ and using quantum mechanics to predict the effect this has on the N-N bond via its length and vibrational stetching mode. Such species are very unlikely to be easily observed for verification.

I occasionally notice that posts that first appeared here many years ago suddenly attract attention.

Earlier, I explored the choreography or “timing”, of what might be described as the curly arrows for a typical taught reaction mechanism, the 1,4-addition of a nucleophile to an unsaturated carbonyl compound (scheme 1). I am now going to explore the consequences of changing one of the actors by adding the nucleophile to an unsaturated imine rather than carbonyl compound (scheme 2).

A little more than a year ago, a ChemRxiv pre-print appeared bearing the title referenced in this post,[cite]10.26434/chemrxiv.8009633.v1[/cite] which immediately piqued my curiosity. The report presented persuasive evidence, in the form of trapping experiments, that dicarbon or C ₂ had been formed by the following chemical synthesis.