In the previous post, I looked at a class of molecule known as hexaphyrins, inspecting bond length alternation (BLA) at the so-called meso position, the carbon atom joining two pyrrole rings. A search of the difference in bond lengths at this position had shown two significant clusters of crystal structures. Molecules in the bottom left of this diagram shows little or no bond length alternation.
The theme of the last three posts derives from the recently reported claimed experimental observation of bond length alternation (BLA) in cyclo[18]carbon, a ring of just 18 carbon atoms.[cite]10.1126/science.aay1914[/cite] Having found that different forms of quantum calculation seem to find this property particularly difficult to agree upon, not only for cyclocarbon but for twisted lemniscular annulenes (which contain CH rather than just C
In the previous posts, I tried to track down the onset of bond length alternation ( BLA ) as a function of ring size in aromatic cyclocarbons, finding the answer varied dramatically depending on the type of method used to calculate it. So here I change the system to an unusual kind of aromatic ring, the leminiscular or figure-eight annulene series. ♥ I explore the Kekulé vibration for such species
In the previous post, I looked at the so-called Kekulé vibration of cyclo[18]carbon using various quantum methods and basis sets. Because some of these procedures can take a very long time, I could not compare them using the same high-quality consistent atom basis set for the carbon (Def2-TZVPP). Here I try to start to do this using the smaller six and ten carbon rings to see what trends might emerge.
I have discussed the vibration in benzene known as the Kekulé mode in other posts, the first of which was all of ten years ago.
In the pipeline reports on an intriguing new ring system acting as an isostere for morpholine. I was interested in how the conformation of this ring system might be rationalised electronically and so I delved into the article.[cite]10.1021/acs.jmedchem.9b00348[/cite] Here I recount what I found.
I have previously looked at the topic of hydrogen bonding interactions from the hydrogen of chloroform Here I generalize C-H…O interactions by conducting searches of the CSD (Cambridge structure database) as a function of the carbon hybridisation. I am going to jump straight to a specific molecule XEVJIR (DOI: 10.5517/cc5fgpq) identified from the searches appended to this post as interesting for further
I have had some interesting discussions recently regarding metadata. What emerges is that it can be quite a broadly defined concept and it is clear that a variety of answers might be obtained when asking the simple question “what is it useful for?” Here I set out some of my answers to that question. Metadata vs Data.
The World-Wide-Web is currently celebrating its 30th anniversary; you can get the T-shirt in the CERN visitor centre! Five years on, in May 1994, the first Web conference took place (WWW94) at CERN and now celebrating its own 25th anniversary. That 1994 conference also had various break-out sessions, one of which summarised the state of chemistry on the web at the time.
In August 2016, the launch of a chemistry pre-print service ChemRxiv was announced. I was phoned a day or so later by a staff journalist at C&E News for my opinion.
