In the previous post, I looked at the intramolecular rearrangement of the oxetane carboxylic acid to a lactone, finding the barrier to the Sn2 reaction with retention was unfeasibly high. Here I explore alternatives. This first attempt uses a second molecule of a carboxylic acid (modelled as formic acid for simplicity) to see if it can catalyse the reaction.
Derek Lowe’s blog has a recent post entitled A Downside to Oxetane Acids which picks up on a recent article[cite]10.1021/acs.orglett.2c01402[/cite] describing how these acids are unexpectedly unstable, isomerising to a lactone at a significant rate without the apparent need for any catalyst. This is important because these types of compound occur frequently in the medicinal chemistry literature.
WATOC 2020 was just held in 2022 in Vancouver Canada, over one week. With many lectures held in parallel, it is not possible for one person to cover anything like the topics presented, so this is a personal view of some of those talks that I attended. As happens with many such events, common themes gradually emerge and here I highlight just two that struck me as important for the future of computational chemistry.
I have long been fascinated by polymers of either carbon dioxide, † or carbon monoxide, or combinations of both. One such molecule, referred to as dioxane tetraketone when it was featured on the ACS molecule-of-the-week site and also known as the anhydride of oxalic acid, or more formally 1,4-dioxane-2,3,5,6-tetraone, has been speculated upon for more than a century.[cite]10.1002/cber.19080410335[/cite] The history of
Minds (and memories) can work in wonderful ways. In 1987[cite]10.1021/jo00389a050[/cite] we were looking at the properties of “stable” tetrahedral intermediates formed in carbonyl group reactions. The reaction involved adding phenylhydroxylamine to acetyl cyanide.
Previously, I explored the unusual structure of a molecule with a hydrogen bonded interaction between a phenol and a pyridine. The crystal structure name was RAKQOJ and it had been reported as having almost symmetrical N…H…O hydrogen bonds. This feature had been determined using neutron diffraction crystallography, which is thought very reliable at determining proton positions.
Proton transfers are amongst the most common of all chemical reactions.
The previous examples of four atom systems displaying two layers of aromaticity illustrated how 4 (B 4 ), 8 (C 4 ) and 12 (N 4 ) valence electrons were partitioned into 4n+2 manifolds (respectively 2+2, 6+2 and 6+6). The triplet state molecule B 2 C 2 with 6 electrons partitioned into 2π and 4σ electrons, with the latter following Baird’s aromaticity
In my previous post on the topic, I introduced the concept that data can come in several forms, most commonly as “raw” or primary data and as a “processed” version of this data that has added value. In crystallography, the chemist is interested in this processed version, carried by a CIF file.
The meeting covered the scientific life of Professor Sir Geoffrey Wilkinson from the perspective of collaborators, friends and family and celebrated three anniversaries, the centenary of his birth (2021), the half-century anniversary of the Nobel prize (2023) and 70 years almost to the day (1 April) since the publication of the seminal article on Ferrocene (2022).[cite]10.1021/ja01128a527[/cite] The meeting was organised as “inverse hybrid”
Normally, aromaticity is qualitatively assessed using an electron counting rule for cyclic conjugated rings. The best known is the Hückel 4n+2 rule (n=0,1, etc) for inferring diatropic aromatic ring currents in singlet-state π-conjugated cyclic molecules ‡ and a counter 4n rule which infers an antiaromatic paratropic ring current for the system.
