Posts Tagged ‘Chemical bond’
Sunday, March 24th, 2019
There is a predilection amongst chemists for collecting records; one common theme is the length of particular bonds, either the shortest or the longest. A particularly baffling type of bond is that between the very electronegative F atom and an acid hydrogen atom such as that in OH. Thus short C-N…HO hydrogen bonds are extremely common, as are C-O…HO.‡ But F atoms in C-F bonds are largely thought to be inert to hydrogen bonding, as indicated by the use of fluorine in many pharmaceuticals as inert isosteres.[1] Here I do an up-to-date search of the CSD crystal structure database, which is now on the verge of accumulating 1 million entries, to see if any strong C-F…HO hydrogen bonding may have been recently discovered.
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References
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S. Purser, P.R. Moore, S. Swallow, and V. Gouverneur, "Fluorine in medicinal chemistry", Chem. Soc. Rev., vol. 37, pp. 320-330, 2008. http://dx.doi.org/10.1039/B610213C
Tags:Chemical bond, chemical bonding, Chemical elements, Chemistry, Fluorine, Hydrogen, Hydrogen bond, Intermolecular forces, Natural sciences, perturbation energy, pharmaceuticals, Physical sciences, Refrigerants, search parameters, search query, Supramolecular chemistry
Posted in crystal_structure_mining | No Comments »
Sunday, March 4th, 2018
A bond index (BI) approximately measures the totals of the bond orders at any given atom in a molecule. Here I ponder what the maximum values might be for elements with filled valence shells.
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Tags:Atom, Chemical bond, chemical bonding, chemical properties, Chemistry, Interesting chemistry, metal bond indices, Molecule, Nature, Quantum chemistry, Residential REITs, Resonance, Tennessine, Valence, Valence electron
Posted in Uncategorised | No Comments »
Monday, November 27th, 2017
Previously: “Non-polar” species such as SeMe6, SMe6, ClMe3, ClMe5 all revealed interesting properties for the Se-C, S-C or Cl-C “single” bonds. The latter two examples in particular hinted at internal structures for these single bonds, as manifested by two ELF basins for some of the bonds. Here I take a look at the related molecule where a formal double bond between carbon and the central sulfur atom replacing the single-bond might also hint at octet expansions and hypervalence.
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Tags:Chemical bond, chemical bonding, Chemical polarity, Chemistry, double bond, Hypervalency, Hypervalent molecule, Nature, single bond, Tetravalence, Valence
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Sunday, November 12th, 2017
A few years back, I took a look at the valence-shell electron pair repulsion approach to the geometry of chlorine trifluoride, ClF3 using so-called ELF basins to locate centroids for both the covalent F-Cl bond electrons and the chlorine lone-pair electrons. Whereas the original VSEPR theory talks about five “electron pairs” totalling an octet-busting ten electrons surrounding chlorine, the electron density-based ELF approach located only ~6.8e surrounding the central chlorine and no “octet-busting”. The remaining electrons occupied fluorine lone pairs rather than the shared Cl-F regions. Here I take a look at ClMe3, as induced by the analysis of SeMe6.
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Tags:Chemical bond, chemical bonding, Chemical IT, Chemistry, Chlorine, Covalent bond, Hypervalency, Lone pair, Oxidizing agents, Quantum chemistry, Stereochemistry, Valence, VSEPR theory
Posted in Uncategorised | 5 Comments »
Tuesday, October 24th, 2017
An N-B single bond is iso-electronic to a C-C single bond, as per below. So here is a simple question: what form does the distribution of the lengths of these two bonds take, as obtained from crystal structures?
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Tags:bond, Bond valence method, Chemical bond, chemical bonding, Chemistry, Covalent bond, crystal structure, Nature, Quantum chemistry, search query
Posted in crystal_structure_mining | 2 Comments »
Saturday, September 16th, 2017
Early in 2011, I wrote about how the diatomic molecule Be2 might be persuaded to improve upon its normal unbound state (bond order ~zero) by a double electronic excitation to a strongly bound species. I yesterday updated this post with further suggestions and one of these inspired this follow-up.
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Tags:Be-Be double bond, Be-Be triple bond, Chemical bond, Chemistry, Cs-Cs double bond, Diatomic molecule, free energy, General chemistry, Interesting chemistry, K-K double bond, Li-Li double bond, Molecular geometry, Oxygen, Province/State: Be2, Quantum chemistry, Rb-Rb double bond, Stereochemistry
Posted in Uncategorised | 3 Comments »
Wednesday, September 6th, 2017
Tags:bond, Chemical bond, chemical bond zoo, City: Aachen, Concepts, Dialectic, Fuzzy concept, Interesting chemistry, Non-classical logic, Psychometrics, triplet excitation energy
Posted in Bond slam | No Comments »
Thursday, April 6th, 2017
Enols are simple compounds with an OH group as a substituent on a C=C double bond and with a very distinct conformational preference for the OH group. Here I take a look at this preference as revealed by crystal structures, with the theoretical explanation.
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Tags:Chemical bond, chemical bonding, Chemistry, Conformational isomerism, constrained search, Enol, free energy, Gauche effect, Hydrogen bond, Isomerism, Java, Physical organic chemistry, search query, Stereochemistry, Supramolecular chemistry
Posted in crystal_structure_mining, reaction mechanism | 2 Comments »
Friday, March 10th, 2017
George Olah passed away on March 8th. He was part of the generation of scientists in the post-war 1950s who had access to chemical instrumentation that truly revolutionised chemistry. In particular he showed how the then newly available NMR spectroscopy illuminated structures of cations in solvents such “Magic acid“. The obituaries will probably mention his famous “feud” with H. C. Brown over the structure of the norbornyl cation (X=CH2+), implicated in the mechanism of many a solvolysis reaction that characterised the golden period of physical organic chemistry just before and after WWII.
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Tags:2-Norbornyl cation, aqueous solutions, Chemical bond, chemical instrumentation, Chemistry, George Andrew Olah, George Olah, Interesting chemistry, Ion association, Magic acid, Michael Dewar, Molecule, Nature, Physical organic chemistry, Reactive intermediates, spectroscopy
Posted in Uncategorised | 17 Comments »