Posts Tagged ‘search query’
Thursday, 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.[1] Here I take a brief look at some of these systems.
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References
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J.B. Lambert, Y. Zhao, H. Wu, W.C. Tse, and B. Kuhlmann, "The Allyl Leaving Group Approach to Tricoordinate Silyl, Germyl, and Stannyl Cations", Journal of the American Chemical Society, vol. 121, pp. 5001-5008, 1999. http://dx.doi.org/10.1021/ja990389u
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 »
Sunday, March 5th, 2017
Cyclobutadiene is one of those small iconic molecules, the transience and instability of which was explained theoretically long before it was actually detected in 1965.[1] Given that instability, I was intrigued as to how many crystal structures might have been reported for this ring system, along with the rather more stable congener cyclo-octatetraene. Here is what I found.
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References
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L. Watts, J.D. Fitzpatrick, and R. Pettit, "Cyclobutadiene", Journal of the American Chemical Society, vol. 87, pp. 3253-3254, 1965. http://dx.doi.org/10.1021/ja01092a049
Tags:antiaromaticity, Chemistry, cyclobutadiene, Instability, Nature, Physical organic chemistry, Physics, search query
Posted in crystal_structure_mining | 4 Comments »
Monday, December 19th, 2016
I am completing my survey of the vote for molecule of the year candidates, which this year seems focused on chemical records of one type or another.
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Tags:chemical publishing, chemical records, human chemical perception, Interesting chemistry, Matter, metal, Molecule, Nature, search query, search software, Voting
Posted in crystal_structure_mining | 2 Comments »
Friday, December 16th, 2016
Here is a third candidate for the C&EN “molecule of the year” vote. This one was shortlisted because it is the first example of a metal-nitrogen complex exhibiting single, double and triple bonds from different nitrogens to the same metal[1] (XUZLUB has a 3D display available at DOI: 10.5517/CC1JYY6M). Since no calculation of its molecular properties was reported, I annotate some here.
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References
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E.P. Beaumier, B.S. Billow, A.K. Singh, S.M. Biros, and A.L. Odom, "A complex with nitrogen single, double, and triple bonds to the same chromium atom: synthesis, structure, and reactivity", Chemical Science, vol. 7, pp. 2532-2536, 2016. http://dx.doi.org/10.1039/c5sc04608d
Tags:10.14469, chemical shifts, expert chemical knowledge, Interesting chemistry, metal, metal-nitrogen complex exhibiting single, search query
Posted in crystal_structure_mining | 10 Comments »
Thursday, December 1st, 2016
Following on from a search for long C-C bonds, here is the same repeated for C=C double bonds.
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Tags:Chemical bond, chemical bonding, Chemical nomenclature, Chemistry, Conjugated system, double bond, energy, Interesting chemistry, Nature, Nonmetal, Organic chemistry, Physical organic chemistry, search query, Substituent
Posted in crystal_structure_mining | 2 Comments »
Wednesday, November 30th, 2016
In an earlier post, I searched for small C-C-C angles, finding one example that was also accompanied by an apparently exceptionally long C-C bond (2.18Å). But this arose from highly unusual bonding giving rise not to a single bond order but one closer to one half! How long can a “normal” (i.e single) C-C bond get, a question which has long fascinated chemists.
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Tags:Aviation, Bond order, Carbon–carbon bond, Chemical bond, chemical bonding, Interesting chemistry, naive search, search query, single bond
Posted in crystal_structure_mining | No Comments »
Tuesday, June 21st, 2016
Tags:Asymmetric hydrogenation, benzene, benzo, Electrophile, Furan, Indole, Pyridine, Pyrrole, search query, Simple aromatic rings, Substitution reaction, Thiophene
Posted in crystal_structure_mining | No Comments »
Monday, June 13th, 2016
Previously, I looked at the historic origins of the so-called π-complex theory of metal-alkene complexes. Here I follow this up with some data mining of the crystal structure database for such structures.
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Tags:alkene, alkene-metal complex, alkyne, Bond length, Carbon–carbon bond, Chemical bond, chemical bonding, Cluster chemistry, Conquest structure editor, Coordination complex, data mining, double bond, editor, filled metal orbital, metal, metal-alkene complexes, metal-alkyne complexes, metal-carbon bonds, Pi backbonding, search query, Structural formula, Transition metal alkyne complex
Posted in crystal_structure_mining | No Comments »
Wednesday, May 25th, 2016
The substitution of a nucleofuge (a good leaving group) by a nucleophile at a carbon centre occurs with inversion of configuration at the carbon, the mechanism being known by the term SN2 (a story I have also told in this post). Such displacement at silicon famously proceeds by a quite different mechanism, which I here quantify with some calculations.
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Tags:Berry mechanism, Elimination reaction, energy, energy barrier, energy profile, free energy, Leaving group, lower energy orientation, Molecular geometry, Organic reactions, overall free energy, Pseudorotation, search query, SN2 reaction, Stereochemistry, Trigonal bipyramidal molecular geometry
Posted in reaction mechanism | No Comments »
Wednesday, May 11th, 2016
I have previously commented on the Bürgi–Dunitz angle, this being the preferred approach trajectory of a nucleophile towards the electrophilic carbon of a carbonyl group. Some special types of nucleophile such as hydrazines (R2N-NR2) are supposed to have enhanced reactivity[1] due to what might be described as buttressing of adjacent lone pairs. Here I focus in on how this might manifest by performing searches of the Cambridge structural database for intermolecular (non-bonded) interactions between X-Y nucleophiles (X,Y= N,O,S) and carbonyl compounds OC(NM)2.
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References
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G. Klopman, K. Tsuda, J. Louis, and R. Davis, "Supernucleophiles—I", Tetrahedron, vol. 26, pp. 4549-4554, 1970. http://dx.doi.org/10.1016/S0040-4020(01)93101-1
Tags:Bases, Bürgi–Dunitz angle, Carbonyl, Chemical IT, Electrophile, Ester, Flippin–Lodge angle, Functional groups, hydrazine, non-metal attachments, Nucleophile, Physical organic chemistry, search query, Superbase
Posted in crystal_structure_mining | 1 Comment »