April 1st, 2017
In a comment appended to an earlier post, I mused about the magnitude of the force constant relating to the interconversion between a classical and a non-classical structure for the norbornyl cation. Most calculations indicate the force constant for an “isolated” symmetrical cation is +ve, which means it is a true minimum and not a transition state for a [1,2] shift. The latter would have been required if the species equilibrated between two classical carbocations. I then pondered what might happen to both the magnitude and the sign of this force constant if various layers of solvation and eventually a counter-ion were to be applied to the molecule, so that a bridge of sorts between the different states of solid crystals, superacid and aqueous solutions might be built.
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Tags: Carbocations, chemical bonding, Chemistry, constant matrix/search direction, continuum model for water, gas phase, Paul Schleyer, Physical organic chemistry, potential energy surface, Reactive intermediates, superacid and aqueous solutions
Posted in crystal_structure_mining, Interesting chemistry, reaction mechanism | 7 Comments »
March 31st, 2017
Nowadays, data supporting most publications relating to the synthesis of organic compounds is more likely than not to be found in associated “supporting information” rather than the (often page limited) article itself. For example, this article[cite]10.1021/jacs.6b13229[/cite] has an SI which is paginated at 907; almost a mini-database in its own right!† Here I ponder whether such dissemination of data is FAIR (Findable, accessible, interoperable and re-usable).[cite]10.1038/sdata.2016.18[/cite]
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Tags: Carbon, chemical databases, chemical graveyard, chemical spectra, Chemistry, digital signature, Nature, Organic, Organic chemistry, Organic compound, Organic food, search engines, Technology/Internet
Posted in Chemical IT | 3 Comments »
March 31st, 2017
Occasionally one comes across a web site that manages to combine being unusual, interesting and also useful. Thus www.molinsight.net is I think a unique chemistry resource for blind and visually impaired students.
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Tags: Chemistry, Electromagnetic radiation, Infrared, Infrared spectroscopy, Multimodal interaction, Nuclear magnetic resonance, open source chemical structure editors, Sonification, spectroscopy, stereochemical utilities
Posted in Interesting chemistry | No Comments »
March 30th, 2017
In an era when alternative facts and fake news afflict us, the provenance of scientific data becomes ever more important. Especially if that data is available as open access and exploitable by others for both valid scientific reasons but potentially also by those with other motives. Here I consider the audit trail that might serve to establish data provenance in one typical situation in chemistry, the acquisition of NMR instrumental data.
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Tags: Acquisition, Archival science, author, collection software, Company: NMR, data, Data management, data processing software, Evidence law, instrument data collection software, local authentication systems, Mestrenova, MestreNova system, Nuclear magnetic resonance, principal investigator, Provenance, Scientific method, service manager, spectrometer software, supervisor, Technology/Internet, Terminology
Posted in Chemical IT | 2 Comments »
March 25th, 2017
The previous post demonstrated the simple iso-electronic progression from six-coordinate carbon to five coordinate nitrogen. Here, a further progression to oxygen is investigated computationally.
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Tags: animation, Chemical bond, Chemistry, Matter, Nitrogen, Quantum chemistry
Posted in Bond slam, Hypervalency | 4 Comments »
March 25th, 2017
A few years back I followed a train of thought here which ended with hexacoordinate carbon, then a hypothesis rather than a demonstrated reality. That reality was recently confirmed via a crystal structure, DOI:10.5517/CCDC.CSD.CC1M71QM[cite]10.1002/anie.201608795[/cite]. Here is a similar proposal for penta-coordinate nitrogen.
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Tags: aromatic systems, Chemistry, Hexacoordinate, Hypotheses, Matter, Molecular geometry, Stereochemistry
Posted in Bond slam, crystal_structure_mining, Hypervalency, Interesting chemistry | 1 Comment »
March 23rd, 2017
It is not only the non-classical norbornyl cation that has proved controversial in the past. A colleague mentioned at lunch (thanks Paul!) that tri-coordinate group 14 cations such as R3Si+ have also had an interesting history.[cite]10.1021/ja990389u[/cite] Here I take a brief look at some of these systems.
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Tags: 2-Norbornyl cation, Carbocations, chemical bonding, Chemistry, metal, Physical organic chemistry, Reactive intermediates, search query, tri-coordinate
Posted in crystal_structure_mining | 8 Comments »
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 »
March 19th, 2017
The Wikipedia entry on peroxydisulfate is quite short (as of today). But I suspect this article may change things.[cite]10.1038/s41559-017-0083[/cite].
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Tags: metal salts, Peroxydisulfate
Posted in crystal_structure_mining, Interesting chemistry | No Comments »
March 19th, 2017
A pyrophoric metal is one that burns spontaneously in oxygen; I came across this phenomenon as a teenager doing experiments at home. Pyrophoric iron for example is prepared by heating anhydrous iron (II) oxalate in a sealed test tube (i.e. to 600° or higher). When the tube is broken open and the contents released, a shower of sparks forms. Not all metals do this; early group metals such as calcium undergo a different reaction releasing carbon monoxide and forming calcium carbonate and not the metal itself. Here as a prelude to the pyrophoric reaction proper, I take a look at this alternative mechanism using calculations.
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Tags: Aluminium, calculated free energy barrier, Carbon monoxide, Chemical elements, Chemistry, higher activation energy, Iron, Matter, metal, metal oxalates, Oxide, pyrophoric metal, Pyrophoricity, Reducing agents
Posted in crystal_structure_mining, reaction mechanism | 1 Comment »