In the previous post, I showed the geometries of three large cyclic porphyrins, as part of an article[cite]10.1038/s41557-019-0398-3[/cite] on exploring the aromaticity of large 4n+2 cyclic rings. One of them had been induced into a “figure-eight” or lemniscular conformation, as shown below.
Dispersion attraction effects on the computed geometry of a leminscular dodecaporphyrin.
January 1st, 2021Global aromaticity at the nanoscale.
December 31st, 2020Here is another of the “large” molecules in the c&e news shortlist for molecule-of-the-year, 2020. This one is testing the Hückel 4n+2 rule out to a value never before seen (n = 40, or 162 π-electrons).[cite]10.1038/s41557-019-0398-3[/cite] The take-home message is that this rule seems to behave well in predicting global aromaticity even at this sort of scale!
Tying different knots in a molecular strand.
December 30th, 2020The title derives from an article[cite]10.1038/s41586-020-2614-0[/cite] which was shortlisted for the annual c&en molecule of the year 2020 awards (and which I occasionally cover here). In fact this year’s overall theme is certainly large molecules, the one exception being a smaller molecule with a quadruple bond to boron, a theme I have already covered here.
Is cyanogen chloride (fluoride) a source of C⩸N(+)? More mechanistic insights.
December 4th, 2020I asked the question in my previous post. A computational mechanism revealed that AlCl3 or its dimer Al2Cl6 could catalyse a concerted 1,1-substitution reaction at the carbon of Cl-C≡N, with benzene displacing chloride which is in turn captured by the Al. Unfortunately the calculated barrier for this simple process was too high for a reaction apparently occuring at ~room temperatures. Comments on the post suggested using either a second AlCl3 or a proton to activate the carbon of the C≡N group by coordination on to nitrogen. A second suggestion was to involve di-cationic electrophiles. Here I report the result of implementing the N-coordinated model below.
Is cyanogen chloride (fluoride) a source of C⩸N(+)?
November 28th, 2020In 2010 I recounted the story of an organic chemistry tutorial, in which I asked the students the question “how would you synthesize 3-nitrobenzonitrile“.
An interesting aromatic molecule found in Titan’s atmosphere: Cyclopropenylidene
November 7th, 2020Cyclopropenylidene must be the smallest molecule to be aromatic due to π-electrons, with just three carbon atoms and two hydrogen atoms. It has now been detected in the atmosphere of Titan, one of Saturn’s moons[cite]10.3847/1538-3881/abb679[/cite] and joins benzene, another aromatic molecule together with the protonated version of cyclopropenylidene, C3H3+ also found there.
A new example of a quadruple bond from carbon – to Fe.
November 7th, 2020Way back in 2010, I was writing about an experience I had just had during an organic chemistry tutorial, which morphed into speculation as to whether a carbon atom might sustain a quadruple bond to nitrogen. A decade on, and possibly approaching 100 articles by many authors on the topic, quadruple bonds to carbon continue to fascinate. Now an article as appeared[cite]10.1039/d0cp03436c[/cite] repeating this speculation for a carbon to iron quadruple bond,‡ in the very simple species C⩸Fe(CO)3 (see also a Rh-B equivalent[cite]10.1021/acs.jpclett.9b03484[/cite]). This is particularly exciting because of the very real prospect of synthesising this species and perchance getting a crystal structure (something not possible with most of the other quadruply bonded carbon systems studied to date).
Internet Archeology: an example of a revitalised molecular resource with a new activity now built in.
November 5th, 2020In Internet terms, 23 years ago is verging on pre-history. Much of what was happening around 1997 on the Web was still highly experimental and so its worth taking a look at some of this to see how it has survived or whether it can be “curated” into a form that would still be useful. I had noted in my earlier comment a site which early on had become non-functional and then speculated whether any volunteers might have suggestions for how to best rescue it.
Trimerous pericyclic reactions: what is the effect of changing the electron count by two?
November 2nd, 2020In an earlier post, I pondered on how the “arrow pushing” for the thermal pericyclic reactions of some annulenes (cyclic conjugated hydrocarbons) could be represented in terms of either two separate electrocyclic reactions or of one cycloaddition reaction. Each reaction is governed by selection rules which can be stated in terms of the anticipated aromaticity of the pericyclic transition state as belonging to a 4n or a 4n+2 class. This in turn determines whether the topology of the transition state belongs to a class of aromatic species known as either Hückel or Möbius. Here I play with the observation that by adding or removing two electrons from the molecule, the two classes 4n and 4n+2 can be swapped. What happens to the aromaticities of the transition states if that is done?
Room-temperature superconductivity in a carbonaceous sulfur hydride!
October 17th, 2020The title of this post indicates the exciting prospect that a method of producing a room temperature superconductor has finally been achived[cite]10.1038/s41586-020-2801-z[/cite]. This is only possible at enormous pressures however; >267 gigaPascals (GPa) or 2,635,023 atmospheres.