March 7th, 2016
Tags: Academic publishing, chemical, chemical information division, Chemical nomenclature, chemical structures, Chemical substance, chemical/x-wavefunction, Cheminformatics, City: San Diego, content media, data repository search, format type chemical/x-* , Identifiers, Imperial College, Imperial College London, International Chemical Identifier, JSON, media types, multipurpose internet media extensions, ORCiD, PDF, potential such systems, research data management, Search queries, Technical communication, Technology/Internet
Posted in Chemical IT | 2 Comments »
February 24th, 2016
At the precise moment I write this, there is information about 108,230,950 organic and inorganic chemical substances from the World's disclosed chemistry. So it was with a sense of curiosity that I came across this article in the American Mineralogist[1] entitled "Earth’s “missing” minerals" (the first in a series of articles apparently planned on the topic of the missing ones). The abstract is particularly interesting and whilst I encourage you to go read the article itself, I will quote some eye-catching observations from just this abstract:
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References
- R.M. Hazen, G. Hystad, R.T. Downs, J.J. Golden, A.J. Pires, and E.S. Grew, "Earth’s “missing” minerals", American Mineralogist, vol. 100, pp. 2344-2347, 2015. https://doi.org/10.2138/am-2015-5417
Tags: inorganic chemical substances, Mineral, Mineralogist, natural products
Posted in Interesting chemistry | No Comments »
February 21st, 2016
Hypervalency is defined as a molecule that contains one or more main group elements formally bearing more than eight electrons in their valence shell. One example of a molecule so characterised was CLi6[1] where the description "“carbon can expand its octet of electrons to form this relatively stable molecule“ was used. Yet, in this latter case, the octet expansion is in fact an illusion, as indeed are many examples that are cited. The octet shell remains resolutely un-expanded. Here I will explore the tiny molecule CH3F2- where two extra electrons have been added to fluoromethane.
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References
- H. Kudo, "Observation of hypervalent CLi6 by Knudsen-effusion mass spectrometry", Nature, vol. 355, pp. 432-434, 1992. https://doi.org/10.1038/355432a0
Tags: Antibonding molecular orbital, Atomic orbital, Block, chemical bonding, Covalent bond, energy, Hypervalent molecule, hypervalent systems, Molecular orbital, Molecular orbital diagram, Octet rule, Periodic table, Valence
Posted in Bond slam, Hypervalency | 1 Comment »
February 9th, 2016
The phenomenon of bond stretch isomerism, two isomers of a compound differing predominantly in just one bond length, is one of those chemical concepts that wax and occasionally wane.[1] Here I explore such isomerism for the elements Ge, Sn and Pb.
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References
- J.A. Labinger, "Bond-stretch isomerism: a case study of a quiet controversy", Comptes Rendus. Chimie, vol. 5, pp. 235-244, 2002. https://doi.org/10.1016/s1631-0748(02)01380-2
Tags: a Jahn-Teller, Bond length, chemical concepts, Chemical substance, Company: Ge, Coordination complex, energy, energy difference, Entertainment/Culture, Hydrogen bond, Isomer, Isomerism, Length, Molecular geometry, Organic chemistry, results of a search, search both bond stretch isomers, SN
Posted in crystal_structure_mining, Historical | 1 Comment »
February 7th, 2016
The geometry of cyclo-octatetraenes differs fundamentally from the lower homologue benzene in exhibiting slow (nuclear) valence bond isomerism rather than rapid (electronic) bond-equalising resonance. In 1992 Anderson and Kirsch[1] exploited this property to describe a simple molecular balance for estimating how two alkyl substituents on the ring might interact via the (currently very topical) mechanism of dispersion (induced-dipole-induced-dipole) attractions. These electron correlation effects are exceptionally difficult to model using formal quantum mechanics and are nowadays normally replaced by more empirical functions such as Grimme's D3BJ correction.[2] Here I explore aspects of how the small molecule below might be used to investigate the accuracy of such estimates of dispersion energies.
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References
- J.E. Anderson, and P.A. Kirsch, "Structural equilibria determined by attractive steric interactions. 1,6-Dialkylcyclooctatetraenes and their bond-shift and ring inversion investigated by dynamic NMR spectroscopy and molecular mechanics calculations", Journal of the Chemical Society, Perkin Transactions 2, pp. 1951, 1992. https://doi.org/10.1039/p29920001951
- S. Grimme, S. Ehrlich, and L. Goerigk, "Effect of the damping function in dispersion corrected density functional theory", Journal of Computational Chemistry, vol. 32, pp. 1456-1465, 2011. https://doi.org/10.1002/jcc.21759
Tags: dispersion, energy, Entropy, lowest energy, lowest energy pose, Physical organic chemistry, Potential theory
Posted in General | No Comments »
February 1st, 2016
I attended the first (of a proposed five) workshops organised by LEARN (an EU-funded project that aims to ...Raise awareness in research data management (RDM) issues & research policy) on Friday. Here I give some quick bullet points relating to things that caught my attention and or interest. The program (and Twitter feed) can be found at https://learnrdm.wordpress.com where other's comments can also be seen.
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Tags: Academic publishing, European Union, first Open Scientist, first secretary, Free culture movement, Henry Oldenburg, Jean Claude Bradley, Open access, Open data, Open science, RDM, Research, researcher, Royal Society, Science, Scientific method, Scientific misconduct, scientist, Technology/Internet
Posted in Chemical IT | 1 Comment »
January 31st, 2016
Six years ago, I posted on the nature of a then recently reported[1] Cr-Cr quintuple bond. The topic resurfaced as part of the discussion on a more recent post on NSF3, and a sub-topic on the nature of the higher order bonding in C2. The comment made a connection between that discussion and the Cr-Cr bond alluded to above. I responded briefly to that comment, but because I want to include 3D rotatable surfaces, I expand the discussion here and not in the comment.‡
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References
- C. Hsu, J. Yu, C. Yen, G. Lee, Y. Wang, and Y. Tsai, "Quintuply‐Bonded Dichromium(I) Complexes Featuring Metal–Metal Bond Lengths of 1.74 Å", Angewandte Chemie International Edition, vol. 47, pp. 9933-9936, 2008. https://doi.org/10.1002/anie.200803859
Tags: Chemical bond, chemical bonding, Electron, Electron configuration, energy, Molecular orbital, Multi-configurational self-consistent field, Quantum chemistry, quintuple bond, search term, Transition metal, Valence bond theory
Posted in General, Interesting chemistry | 6 Comments »
January 20th, 2016
The original strategic objective of my PhD researches in 1972-74 was to explore how primary kinetic hydrogen isotope effects might be influenced by the underlying structures of the transition states involved. Earlier posts dealt with how one can construct quantum-chemical models of these transition states that fit the known properties of the reactions. Now, one can reverse the strategy by computing the expected variation with structure to see if anything interesting might emerge, and then if it does, open up the prospect of further exploration by experiment. Here I will use the base-catalysed enolisation of 1,3-dimethylindolin-2-ones and the decarboxylation of 3-indole carboxylates to explore this aspect.
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Tags: aqueous solution, Brian Challis, can construct quantum-chemical models, computed free energy barrier matches, Dan Singleton, free energy barrier, free energy barriers, Kinetic isotope effect, Organic chemistry, Physical organic chemistry, quantum-chemical models, supervisor
Posted in reaction mechanism | No Comments »
January 16th, 2016
The post on applying VSEPR ("valence shell electron pair repulsion") theory to the geometry of ClF3 has proved perennially popular. So here is a follow-up on another little molecue, F3SN. As the name implies, it is often represented with an S≡N bond. Here I take a look at the conventional analysis.
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Tags: Chemical bond, chemical bonding, Electron, Lone pair, Molecular geometry, Octet rule, Quantum chemistry, Stereochemistry, Tetrahedral molecular geometry, Theoretical chemistry, Valence, VSEPR theory
Posted in Hypervalency | 110 Comments »