Archive for the ‘Interesting chemistry’ Category

Herapathite: an example of (double?) serendipity.

Thursday, October 14th, 2021

On October 13, 2021, the historical group of the Royal Society of Chemistry organised a symposium celebrating ~150 years of the history of (molecular) chirality. We met for the first time in person for more than 18 months and were treated to a splendid and diverse program about the subject. The first speaker was Professor John Steeds from Bristol, talking about the early history of light and the discovery of its polarisation. When a slide was shown about herapathite[1] my “antennae” started vibrating. This is a crystalline substance made by combining elemental iodine with quinine in acidic conditions and was first discovered by William Herapath as long ago as 1852[2] in unusual circumstances. Now to the serendipity!

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References

  1. B. Kahr, J. Freudenthal, S. Phillips, and W. Kaminsky, "Herapathite", Science, vol. 324, pp. 1407-1407, 2009. http://dx.doi.org/10.1126/science.1173605
  2. W.B. Herapath, "XXVI. On the optical properties of a newly-discovered salt of quinine, which crystalline substance possesses the power of polarizing a ray of light, like tourmaline, and at certain angles of rotation of depolarizing it, like selenite", The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, vol. 3, pp. 161-173, 1852. http://dx.doi.org/10.1080/14786445208646983

More record breakers for the anomeric effect involving C-N bonds.

Saturday, September 4th, 2021

An earlier post investigated large anomeric effects involving two oxygen atoms attached to a common carbon atom.

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Tetra-isopropylmethane and tetra-t-butylmethane.

Tuesday, August 17th, 2021

The homologous hydrocarbon series R4C is known for R=Me as neopentane and for R=Et as 3,3-diethylpentane. The next homologue, R=iPr bis(3,3-isopropyl)-2,4-dimethylpentane is also a known molecule[1] for which a crystal structure has been reported (DOI: https://doi.org/10.5517/cc4wvnh). The final member of the series, R= tbutyl is unknown. Here I have a look at some properties of the last two of these highly hindered hydrocarbons.

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References

  1. S.I. Kozhushkov, R.R. Kostikov, A.P. Molchanov, R. Boese, J. Benet-Buchholz, P.R. Schreiner, C. Rinderspacher, I. Ghiviriga, and A. de Meijere, "Tetracyclopropylmethane: A Unique Hydrocarbon with S4 Symmetry", Angewandte Chemie International Edition, vol. 40, pp. 180-183, 2001. http://dx.doi.org/10.1002/1521-3773(20010105)40:1<180::AID-ANIE180>3.0.CO;2-K

Sterically stabilized cyclopropenylidenes. An example of Octopus publishing?

Sunday, August 15th, 2021

Whilst I was discussing the future of scientific publication in the last post, a debate was happening behind the scenes regarding the small molecule cyclopropenylidene. This is the smallest known molecule displaying π-aromaticity, but its high reactivity means that it is unlikely to be isolated in the condensed phase. A question in the discussion asked if substituting it with a large sterically hindering group such as R=Et3C might help prevent its dimerisation and hence allow for isolation of the monomer so that its properties can be studied.

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Molecules with very large dipole moments: cyclopropenium acetylide

Sunday, July 11th, 2021

Occasionally, someone comments about an old post here, asking a question. Such was the case here, when a question about the dipole moment of cyclopropenylidene arose. It turned out to be 3.5D, but this question sparked a thought about the related molecule below.

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A closer look at that fourth bond in C2.

Wednesday, June 2nd, 2021

From the last few posts here, you might have noticed much discussion about how the element carbon might sustain a quadruple bond. The original post on this topic from some years ago showed the molecular orbitals of the species CN+, which included two bonding π-types and a low lying nodeless bonding σ-orbital, all with double occupancies and adding up to a triple bond. Discussing now C2 itself, there are two remaining orbitals for consideration which we will for the purpose here call the highest occupied σ-MO or HOσMO (Σu) and the lowest unoccupied σ-MO or LUσMO (Σg) and which are more mysterious.

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A reality-based suggestion for a molecule with a metal M⩸N quadruple bond.

Thursday, May 13th, 2021

I noted in an earlier post the hypothesized example of (CO)3Fe⩸C[1] as exhibiting a carbon to iron quadruple bond and which might have precedent in known five-coordinate metal complexes where one of the ligands is a “carbide” or C ligand. I had previously mooted that the Fe⩸C combination might be replaceable by an isoelectronic Mn⩸N pair which could contain a quadruple bond to the nitrogen. An isoelectronic alternative to FeC could also be FeN+. Here I explore the possibility of realistic candidates for such bonded nitrogen.

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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

A suggestion for a molecule with a M⩸C quadruple bond with trigonal metal coordination.

Thursday, May 13th, 2021

The proposed identification of molecules with potential metal to carbon quadruple bonds, in which the metal exhibits trigonal bipyramidal coordination rather than the tetrahedral modes which have been proposed in the literature[1],[2],[3] leads on to asking whether simple trigonal coordination at the metal can also sustain this theme?

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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
  2. A.J. Kalita, S.S. Rohman, C. Kashyap, S.S. Ullah, I. Baruah, L.J. Mazumder, P.P. Sahu, and A.K. Guha, "Is a transition metal–silicon quadruple bond viable?", Physical Chemistry Chemical Physics, vol. 23, pp. 9660-9662, 2021. http://dx.doi.org/10.1039/d1cp00598g
  3. L.F. Cheung, T. Chen, G.S. Kocheril, W. Chen, J. Czekner, and L. Wang, "Observation of Four-Fold Boron–Metal Bonds in RhB(BO–) and RhB", The Journal of Physical Chemistry Letters, vol. 11, pp. 659-663, 2020. http://dx.doi.org/10.1021/acs.jpclett.9b03484

What does a double σ-bond along a bond axis look like?

Monday, May 10th, 2021

Introductory chemistry will tell us that a triple bond between say two carbon atoms comprises just one bond of σ-axial symmetry and two of π-symmetry. Increasingly mentioned nowadays is the possibility of a quadruple bond between carbon and either itself or a transition metal, as discussed in the previous post. Such a bond comprises TWO bonds of σ-axial symmetry. Since most people are unfamiliar with such double bonds and in particular with how that second σ-bond sits with the first, I thought it would be interesting to show such an orbital. This one is a localised orbital 41, selected from the previous post for the molecule (PH3)2(CN)2Mo⩸C. (more…)

Two new reality-based suggestions for molecules with a metal M⩸C quadruple bond.

Saturday, May 8th, 2021

Following from much discussion over the last decade about the nature of C2, a diatomic molecule which some have suggested sustains a quadruple bond between the two carbon atoms, new ideas are now appearing for molecules in which such a bond may also exist between carbon and a transition metal atom. A suggested, albeit hypothetical example was C⩸Fe(CO)3[1]. Iron has a [Ar].3d6.4s2 electronic configuration and if we ionise to balance a C4- ligand, the iron becomes formally FeVI or [Ar].3d4. By adding 14 electrons deriving from the seven “bonds” to the 3d4, including a quadruple count from carbon, the Fe formally completes its 18-electron valence shell, as also found in e.g. Ferrocene.

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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