Posts Tagged ‘energy’
Thursday, January 3rd, 2019
There is emerging interest in cyclic conjugated molecules that happen to have triplet spin states and which might be expected to follow a 4n rule for aromaticity.[1] The simplest such system would be the triplet state of cyclobutadiene, for which a non or anti-aromatic singlet state is always found to be lower in energy. Here I explore some crystal structures containing this motif for possible insights.
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References
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A. Kostenko, B. Tumanskii, Y. Kobayashi, M. Nakamoto, A. Sekiguchi, and Y. Apeloig, "Spectroscopic Observation of the Triplet Diradical State of a Cyclobutadiene", Angewandte Chemie International Edition, vol. 56, pp. 10183-10187, 2017. http://dx.doi.org/10.1002/anie.201705228
Tags:antiaromaticity, aromaticity, Conjugated system, crystal structure search, energy, Hückel's rule, Nature, Physical organic chemistry, search query, Triplet state
Posted in Interesting chemistry | No Comments »
Wednesday, August 8th, 2018
White City is a small area in west london created as an exhibition site in 1908, morphing over the years into an Olympic games venue, a greyhound track, the home nearby of the BBC (British Broadcasting Corporation) and most recently the new western campus for Imperial College London.♣ The first Imperial department to move into the MSRH (Molecular Sciences Research Hub) building is chemistry. As a personal celebration of this occasion, I here dedicate three transition states located during my first week of occupancy there, naming them the White City trio following earlier inspiration by a string trio and their own instruments.
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Tags:acetic acid, Acid, Amide, Amine, carboxylic acid, Chemistry, Company: BBC, Company: British Broadcasting Corporation, energy, Ester, exhibition site, free energy barrier, Functional groups, Hydrogen bond, Imperial College, Imperial College London, Ionic product, Newspaper & Magazine Printing Services, Non-ionic product, Olympic games, Organic chemistry, White City Trio
Posted in Interesting chemistry | 6 Comments »
Tuesday, August 7th, 2018
Harnessing FAIR data is an event being held in London on September 3rd; no doubt all the speakers will espouse its virtues and speculate about how to realize its potential.♥ Admirable aspirations indeed. Capturing hearts and minds also needs lots of real life applications! Whilst assembling a forthcoming post on this blog, I realized I might have one nice application which also pushes the envelope a bit further, in a manner that I describe below.
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Tags:Academic publishing, chemical context, Code, data, DataCite, energy, free energy activation barrier, Identifiers, Information, ISO/IEC 11179, ORCiD, quantum chemical calculations, real life applications, Technical communication
Posted in Interesting chemistry | 9 Comments »
Wednesday, April 18th, 2018
The molecules below were discussed in the previous post as examples of highly polar but formally neutral molecules, a property induced by aromatisation of up to three rings. Since e.g. compound 3 is known only in its protonated phenolic form, here I take a look at the basicity of the oxygen in these systems to see if deprotonation of the ionic phenol form to the neutral polar form is viable.
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Tags:Antiseptics, Aromatization, Chemistry, energy, energy minimum, Hydrogen, Molecule, Neurotoxins, Science
Posted in Interesting chemistry | No Comments »
Friday, April 13th, 2018
In several posts a year or so ago I considered various suggestions for the most polar neutral molecules, as measured by the dipole moment. A record had been claimed[1] for a synthesized molecule of ~14.1±0.7D. I pushed this to a calculated 21.7D for an admittedly hypothetical and unsynthesized molecule. Here I propose a new family of compounds which have the potential to extend the dipole moment for a formally neutral molecule up still further.
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References
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J. Wudarczyk, G. Papamokos, V. Margaritis, D. Schollmeyer, F. Hinkel, M. Baumgarten, G. Floudas, and K. Müllen, "Hexasubstituted Benzenes with Ultrastrong Dipole Moments", Angewandte Chemie International Edition, vol. 55, pp. 3220-3223, 2016. http://dx.doi.org/10.1002/anie.201508249
Tags:aromatisation stabilization energy, Chemical polarity, chemical properties, Chemistry, Dipole, Electric dipole moment, Electromagnetism, energy, Moment, Nature, Physical quantities, Physics, Potential theory
Posted in Interesting chemistry | 8 Comments »
Sunday, December 17th, 2017
Alkalides are anionic alkali compounds containing e.g. sodide (Na–), kalide (K–), rubidide (Rb–) or caeside (Cs–). Around 90 examples can be found in the Cambridge structure database (see DOI: 10.14469/hpc/3453 for the search query and results). So what about the ammonium analogue, ammonide (NH4–)? A quick search of Scifinder drew a blank! So here I take a look at this intriguingly simple little molecule.‡
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Tags:Alkalide, Ammonium, Anions, Atomic physics, Chemistry, electron gas, energy, free-electron gas, Jahn-Teller, kinetic energy density, Matter, Nitrogen, potential energy surface, search query
Posted in Hypervalency | 2 Comments »
Tuesday, August 29th, 2017
The triennial conference is this year located in Munich. With 1500 participants and six parallel sessions, this report can give only a flavour of proceedings.
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Tags:bond dissociation energy, City: Aachen, City: Munich, Dieter Cremer, Edward Valeev, energy, Flavour, Jeremy Harvey, Ken Houk, Leo Radom, Peter Scheiner, Physics, Proceedings, Quark matter, Standard Model, Yitzhak Apeloig
Posted in Interesting chemistry, WATOC reports | No Comments »
Sunday, June 18th, 2017
The iron complex shown below forms the basis for many catalysts.[1] With iron, the catalytic behaviour very much depends on the spin-state of the molecule, which for the below can be either high (hextet) or medium (quartet) spin, with a possibility also of a low spin (doublet) state. Here I explore whether structural information in crystal structures can reflect such spin states.
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References
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M.P. Shaver, L.E.N. Allan, H.S. Rzepa, and V.C. Gibson, "Correlation of Metal Spin State with Catalytic Reactivity: Polymerizations Mediated by α-Diimine–Iron Complexes", Angewandte Chemie International Edition, vol. 45, pp. 1241-1244, 2006. http://dx.doi.org/10.1002/anie.200502985
Tags:catalysis, Catalysts, Chemistry, energy, energy separations, energy span, Fe complex, Homogeneous catalysis, Kumada coupling, Organometallic chemistry, spin-state energy separations, Synergistic catalysis
Posted in crystal_structure_mining | 1 Comment »
Saturday, April 15th, 2017
Back in the early 1990s, we first discovered the delights of searching crystal structures for unusual bonding features.[1] One of the first cases was a search for hydrogen bonds formed to the π-faces of alkenes and alkynes. In those days the CSD database of crystal structures was a lot smaller (<80,000 structures; it’s now ten times larger) and the search software less powerful. So here is an update.
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References
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H.S. Rzepa, M.H. Smith, and M.L. Webb, "A crystallographic AM1 and PM3 SCF-MO investigation of strong OH ⋯π-alkene and alkyne hydrogen bonding interactions", J. Chem. Soc., Perkin Trans. 2, pp. 703-707, 1994. http://dx.doi.org/10.1039/P29940000703
Tags:calculated energy, chemical bonding, Chemistry, Crystal, crystallography, energy, energy calculation, Intermolecular forces, Nature, search query, search software, Supramolecular chemistry
Posted in crystal_structure_mining | 2 Comments »
Monday, March 20th, 2017
The example a few posts back of how methane might invert its configuration by transposing two hydrogen atoms illustrated the reaction mechanism by locating a transition state and following it down in energy using an intrinsic reaction coordinate (IRC). Here I explore an alternative method based instead on computing a molecular dynamics trajectory (MD).
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Tags:animation, chemical reaction, Chemistry, computational chemistry, computed potential energy surface, energy, Gaseous signaling molecules, Hydrogen, kinetic energy, kinetic energy contributions, Methane, Molecular dynamics, Physical chemistry, Quantum chemistry, Reaction coordinate, simulation, Theoretical chemistry
Posted in reaction mechanism | 2 Comments »
