Archive for the ‘Interesting chemistry’ Category

An interesting aromatic molecule found in Titan’s atmosphere: cyclopropylidene.

Saturday, November 7th, 2020

Cyclopropylidene 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[1] and joining benzene, another aromatic molecule and the protonated version C3H3+ there.

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References

  1. C.A. Nixon, A.E. Thelen, M.A. Cordiner, Z. Kisiel, S.B. Charnley, E.M. Molter, J. Serigano, P.G.J. Irwin, N.A. Teanby, and Y. Kuan, "Detection of Cyclopropenylidene on Titan with ALMA", The Astronomical Journal, vol. 160, pp. 205, 2020. http://dx.doi.org/10.3847/1538-3881/abb679

A new example of a quadruple bond from carbon – to Fe.

Saturday, November 7th, 2020

Way 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[1] repeating this speculation for a carbon to iron quadruple bond, in the very simple species C⩸Fe(CO)3. 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).

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References

  1. A.J. Kalita, S.S. Rohman, C. Kashyap, S.S. Ullah, and A.K. Guha, "Transition metal carbon quadruple bond: viability through single electron transmutation", Physical Chemistry Chemical Physics, vol. 22, pp. 24178-24180, 2020. http://dx.doi.org/10.1039/d0cp03436c

Room-temperature superconductivity in a carbonaceous sulfur hydride!

Saturday, October 17th, 2020

The title of this post indicates the exciting prospect that a method of producing a room temperature superconductor has finally been achived[1]. This is only possible at enormous pressures however; >267 gigaPascals (GPa) or 2,635,023 atmospheres.

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References

  1. E. Snider, N. Dasenbrock-Gammon, R. McBride, M. Debessai, H. Vindana, K. Vencatasamy, K.V. Lawler, A. Salamat, and R.P. Dias, "Room-temperature superconductivity in a carbonaceous sulfur hydride", Nature, vol. 586, pp. 373-377, 2020. http://dx.doi.org/10.1038/s41586-020-2801-z

High-performance polythioesters with high chemical recyclability.

Wednesday, September 2nd, 2020

Here I investigate a recent report[1] of a new generation of polyesters with the intrinsic properties of high crystallinity and chemical recyclability. The latter point is key, since many current plastics cannot be easily recycled to a form which can be used to regenerate the original polymer with high yield. Here I show some aspects of this fascinating new type of polymer.

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References

  1. C. Shi, M.L. McGraw, Z. Li, L. Cavallo, L. Falivene, and E.Y. Chen, "High-performance pan-tactic polythioesters with intrinsic crystallinity and chemical recyclability", Science Advances, vol. 6, pp. eabc0495, 2020. http://dx.doi.org/10.1126/sciadv.abc0495

Question for the day – Einstein, special relativity and atomic weights.

Saturday, July 25th, 2020

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.

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Fascinating stereoelectronic control in Metaldehyde and Chloral.

Tuesday, June 9th, 2020

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).

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The strongest bond in the universe: revisited ten years on.

Saturday, May 23rd, 2020

I occasionally notice that posts that first appeared here many years ago suddenly attract attention. Thus this post, entitled The strongest bond in the universe, from ten years back, has suddently become the most popular, going from an average of 0-2 hits per day to 92 in a single day on May 22nd (most views appear to originate from India). I can only presume that a university there has set some course work on this topic and Google has helped some of the students identify my post. Well, re-reading something you wrote ten years ago can be unsettling. Are the conclusions still sound? Would I establish my claim the same way now? After all, one picks up a little more experience in ten years. So here is my revisitation.

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Discussion of (the) Room-temperature chemical synthesis of dicarbon – open and transparent science.

Wednesday, May 6th, 2020

A little more than a year ago, a ChemRxiv pre-print appeared bearing the title referenced in this post,[1] which immediately piqued my curiosity. The report presented persuasive evidence, in the form of trapping experiments, that dicarbon or C2 had been formed by the following chemical synthesis. Here I describe some of what happened next, since it perhaps gives some insight into the processes of bringing a scientific result into the open.

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References

  1. K. Miyamoto, S. Narita, Y. Masumoto, T. Hashishin, M. Kimura, M. Ochiai, and M. Uchiyama, "Room-Temperature Chemical Synthesis of C2", 2019. http://dx.doi.org/10.26434/chemrxiv.8009633.v1

A molecular sponge for hydrogen storage- the future for road transport?

Sunday, April 19th, 2020

In the news this week is a report of a molecule whose crystal lattice is capable of both storing and releasing large amounts of hydrogen gas at modest pressures and temperatures. Thus “NU-1501-Al” can absorb 14 weight% of hydrogen. To power a low-polluting car with a 500 km range, about 4-5 kg of hydrogen gas would be need to be stored and released safely. The molecule is of interest since it opens a systematic strategy of synthetically driven optimisation towards a viable ultra-porous storage material,[1] much like a lead drug compound can be optimised.

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References

  1. Z. Chen, P. Li, R. Anderson, X. Wang, X. Zhang, L. Robison, L.R. Redfern, S. Moribe, T. Islamoglu, D.A. Gómez-Gualdrón, T. Yildirim, J.F. Stoddart, and O.K. Farha, "Balancing volumetric and gravimetric uptake in highly porous materials for clean energy", Science, vol. 368, pp. 297-303, 2020. http://dx.doi.org/10.1126/science.aaz8881

The singlet and open shell higher-spin states of [4], [6] and [8]-annulenes and their Kekulé vibrational modes

Wednesday, March 11th, 2020

In 2001, Shaik and co-workers published the first of several famous review articles on the topic A Different Story of π-Delocalization. The Distortivity of π-Electrons and Its Chemical Manifestations[1]. The main premise was that the delocalized π-electronic component of benzene is unstable toward a localizing distortion and is at the same time stabilized by resonance relative to a localized reference structure.  Put more simply, the specific case of benzene has six-fold symmetry because of the twelve C-C σ-electrons and not the six π-electrons. In 2009, I commented here on this concept, via a calculation of the quintet state of benzene in which two of the six π-electrons are excited from bonding into anti-bonding π-orbitals, thus reducing the total formal π-bond orders around the ring from three to one. I focused on a particular vibrational normal mode, which is usefully referred to as the Kekulé mode, since it lengthens three bonds in benzene whilst shortening the other three. In this case the stretching wavenumber increased by ~207 cm-1 when the total π-bond order of benzene was reduced from three to one by spin excitation. In other words, each C-C bond gets longer when the π-electrons are excited, but the C-C bond itself gets stronger (in terms at least of the Kekulé mode). This behaviour is called a violation of Badger’s rule[2] for the relationship between the length of a bond and its stretching force constant. 

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References

  1. S. Shaik, A. Shurki, D. Danovich, and P.C. Hiberty, "A Different Story of π-DelocalizationThe Distortivity of π-Electrons and Its Chemical Manifestations†", Chemical Reviews, vol. 101, pp. 1501-1540, 2001. http://dx.doi.org/10.1021/cr990363l
  2. R.M. Badger, "A Relation Between Internuclear Distances and Bond Force Constants", The Journal of Chemical Physics, vol. 2, pp. 128-131, 1934. http://dx.doi.org/10.1063/1.1749433