I am now inverting the previous question by asking what is the largest angle subtended at a chain of three connected 4-coordinate carbon atoms ? Let’s see if further interesting chemistry can be unearthed. Specifying only angles > 130°, the following distribution is obtained.

The upcoming ACS national meeting in San Diego has a CHED (chemical education division) session entitled Implementing Discovery-Based Research Experiences in Undergraduate Chemistry Courses. I had previously explored what I called extreme gauche effects in the molecule F-S-S-F. Here I take this a bit further to see what else can be discovered about molecules containing bonds between group 16 elements (QA= O, S, Se, Te).

I noted previously that some 8-ring cyclic compounds could exist in either a planar-aromatic or a non-planar-non-aromatic mode, the mode being determined by apparently quite small changes in a ring substituent. Hunting for other examples of such chemistry on the edge, I did a search of the Cambridge crystal database for metal sulfides.

C ₂ (dicarbon) is certainly interesting from a theoretical point of view. Whether or not it can be described as having a quadruple bond has induced much passionate discussion[cite]10.1038/nchem.1263[/cite],[cite]10.1002/anie.201208206[/cite],[cite]10.1002/anie.201301485[/cite],[cite]10.1002/anie.201302350[/cite]. Its occurrence in space and in flames is also well-known.

This is another in the occasional series of “what a neat molecule”. In this case, more of a “what a neat idea”. The s-triazine below, when coordinated to eg ZnI ₂ , forms what is called a metal-organic-framework, or MOF.

Functionalisation of a (hetero)aromatic ring by selectively (directedly) removing protons using the metal lithium is a relative mechanistic newcomer, compared to the pantheon of knowledge on aromatic electrophilic substitution. Investigating the mechanism using quantum calculations poses some interesting challenges, ones I have not previously discussed on this blog.

If you search e.g. Scifinder for N,O-diphenyl hydroxylamine (RN 24928-98-1) there is just one literature citation, to a 1962 patent. Nothing else;

The text books say that cyclohexenone A will react with a Grignard reagent by delivery of an alkyl (anion) to the carbon of the carbonyl ( 1,2-addition ) but if dimethyl lithium cuprate is used, a conjugate 1,4-addition proceeds, to give the product B shown below.

Every once in a while, one encounters a molecule which instantly makes an interesting point.

Alkene metathesis is part of a new generation of synthetic reaction in which a double C=C bond is formed from appropriate reactants where no bond initially exists (another example is the Wittig reaction), with the involvement ^† of a 4-membered-ring metallacyclobutane ring 1 (again, very similar to the Wittig). I thought it might make a good addition to my collection of reaction mechanisms and so as the first step