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Andreas Herburger Dr. Milan Ončák Dr. Chi-Kit Siu Ephrem G. Demissie Jakob Heller Dr. Wai Kit Tang Prof. Dr. Martin K. Beyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(43):10165-10171
Understanding the intrinsic properties of the hydrated carbon dioxide radical anions CO2.−(H2O)n is relevant for electrochemical carbon dioxide functionalization. CO2.−(H2O)n (n=2–61) is investigated by using infrared action spectroscopy in the 1150–2220 cm−1 region in an ICR (ion cyclotron resonance) cell cooled to T=80 K. The spectra show an absorption band around 1280 cm−1, which is assigned to the symmetric C−O stretching vibration νs. It blueshifts with increasing cluster size, reaching the bulk value, within the experimental linewidth, for n=20. The antisymmetric C−O vibration νas is strongly coupled with the water bending mode ν2, causing a broad feature at approximately 1650 cm−1. For larger clusters, an additional broad and weak band appears above 1900 cm−1 similar to bulk water, which is assigned to a combination band of water bending and libration modes. Quantum chemical calculations provide insight into the interaction of CO2.− with the hydrogen-bonding network. 相似文献
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Taye B. Demissie Nataliya Kostenko Stanislav Komorovsky Michal Repisky Johan Isaksson Annette Bayer Kenneth Ruud 《Journal of Physical Organic Chemistry》2015,28(12):723-731
We present a theoretical and experimental study of the structure and nuclear magnetic resonance (NMR) parameters of the pentacarbonyltungsten complexes of η1‐2‐(trimethylstannyl)‐4,5‐dimethylphosphinine, η2‐norbornene, and imidazolidine‐2‐thione. The three complexes have a pseudo‐octahedral molecular structure with the six ligands bonded to the tungsten atom. The η1‐2‐(trimethylstannyl)‐4,5‐dimethylphosphinine‐pentacarbonyl tungsten complex was synthesized for the first time. For all compounds, we present four‐component relativistic calculations of the NMR parameters at the Dirac–Kohn–Sham density functional level of theory using hybrid functionals. These large‐scale relativistic calculations of NMR chemical shifts and spin–spin coupling constants were compared with available experimental data, either taken from the literature or measured in this work. The inclusion of solvent effects modeled using a conductor‐like screening model was found to improve agreement between the calculated and experimental NMR parameters, and our best estimates for the NMR parameters are generally in good agreement with available experimental results. The present work demonstrates that four‐component relativistic theory has reached a level of maturity that makes it a convenient and accurate tool for modeling and understanding chemical shifts and indirect spin–spin coupling constants of organometallic compounds containing heavy elements, for which conventional non‐relativistic theory breaks down. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Helena Dodziuk Taye Beyene Demissie Kenneth Ruud Sławomir Szymański Jarosław Jaźwiński Henning Hopf 《Magnetic resonance in chemistry : MRC》2012,50(6):449-457
The calculated structures of several known and hypothetical cyclophanes with ethylene bridges (cyclophenes) are reported together with experimental and calculated values of their NMR parameters. Of the exchange‐correlation functionals and basis sets used in this work, only the ωB97X‐D/6‐311++G(2d,2p) and ωB97X‐D/cc‐pVQZ yielded values of the Csp3–Csp3 bond length close to the experimental data, although significant differences still remain. As far as the NMR parameters are concerned, except for close‐lying signals, chemical shifts and coupling constants calculated at the ωB97X‐D/cc‐pVQZ level reproduce in most cases the experimental trends. Contrary to the calculations of geometries, an agreement between the values of the NMR parameters obtained at ωB97X‐D/cc‐pVQZ level and the experimental ones is the poorest compared with that of the ωB97X‐D/6‐311++G(2d,2p) one. Taking into account that the results of the different calculations show the same qualitative trends in most cases, we believe that they correctly describe the structure and properties of the hypothetical molecules studied here. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Mercury Methylation by Cobalt Corrinoids: Relativistic Effects Dictate the Reaction Mechanism 下载免费PDF全文
Dr. Taye B. Demissie Brady D. Garabato Prof. Dr. Kenneth Ruud Prof. Dr. Pawel M. Kozlowski 《Angewandte Chemie (International ed. in English)》2016,55(38):11503-11506
The methylation of HgII(SCH3)2 by corrinoid‐based methyl donors proceeds in a concerted manner through a single transition state by transfer of a methyl radical, in contrast to previously proposed reaction mechanisms. This reaction mechanism is a consequence of relativistic effects that lower the energies of the mercury 6p1/2 and 6p3/2 orbitals, making them energetically accessible for chemical bonding. In the absence of spin–orbit coupling, the predicted reaction mechanism is qualitatively different. This is the first example of relativity being decisive for the nature of an observed enzymatic reaction mechanism. 相似文献
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Richard Fjellaksel Damir Dugalic Taye B. Demissie Patrick J. Riss Ole‐Kristian Hjelstuen Rune Sundset Jørn H. Hansen 《Journal of Physical Organic Chemistry》2018,31(7)
Herein, we report a straightforward sequential acylation‐Finkelstein approach to achieve iodination of amine containing bioactives. The utility was demonstrated by successful radiolabelling with 123I in high radiochemical yield. Moreover, microwave‐assisted Finkelstein reaction can be employed to enhance conversion and reaction rates to obtain the desired iodides. The method is of interest for radioiodination of amine‐containing bioactives. The mechanistic details of the iodination process were studied by kinetics and density functional theory calculations, which revealed the mechanistic complexity of the reaction involving amide group anchimeric assistance. We disclose a number of fundamental aspects of amide group anchimeric assistance in substitution reactions. 相似文献
6.
Sławomir Szymański Helena Dodziuk Mariusz Pietrzak Jarosław Jaźwiński Taye Beyene Demissie Henning Hopf 《Journal of Physical Organic Chemistry》2013,26(7):596-600
Extending our earlier findings for [3.3]paracyclophane, NMR line shape studies of the conformational dynamics in [3.2] and [4.3]paracyclophanes are reported, of which the former is conformationally homogeneous and the latter occurs in two enantiomeric forms. For [3.2]paracyclophane, the Arrhenius activation energy Ea = 11.6 ± 0.1 kcal/mol and preexponential factor log (A/s?1) = 12.92 ± 0.07 were found. In [4.3]paracyclophane, the conformational dynamics are quite complicated because, apart from interconversions of each enantiomer into itself proceeding via inversion of the propano bridge with rate constant k1, the enantiomers mutually rearrange with rate constant k2 due to inversion of the butano bridge. The determination of Arrhenius parameters from dynamic 1H spectra of the aromatic protons for these two conformational processes (Ea = 11.2 ± 0.5 kcal/mol and log (A/s?1) = 13.6 ± 0.5 for the former, and Ea = 9.7 ± 0.4 kcal/mol and log (A/s?1) = 13.2 ± 0.4 for the latter) is the highlight of this work. In the investigated temperature range, in [4.3]paracyclophane, the occurrence of other conformational processes beyond those mentioned above can be excluded, because they would produce different line shape patterns than those actually observed. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
7.
Dr. Antony J. Williams Taye B. Demissie Dr. Espen Hansen Dr. Jeanette H. Andersen Dr. Johan Svenson Kirill Blinov Dr. Michal Repisky Dr. Fabian Mohn Dr. Gerhard Meyer Prof. Dr. John‐Sigurd Svendsen Prof. Dr. Kenneth Ruud Prof. Dr. Mikhail Elyashberg Dr. Leo Gross Prof. Dr. Marcel Jaspars Dr. Johan Isaksson 《Angewandte Chemie (International ed. in English)》2012,51(49):12238-12241
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Dodziuk H Szymański S Jaźwiński J Ostrowski M Demissie TB Ruud K Kuś P Hopf H Lin ST 《The journal of physical chemistry. A》2011,115(38):10638-10649
Density functional theory (DFT) quantum chemical calculations of the structure and NMR parameters for highly strained hydrocarbon [2.2]paracyclophane 1 and its three derivatives are presented. The calculated NMR parameters are compared with the experimental ones. By least-squares fitting of the (1)H spectra, almost all J(HH) coupling constants could be obtained with high accuracy. Theoretical vicinal J(HH) couplings in the aliphatic bridges, calculated using different basis sets (6-311G(d,p), and Huz-IV) reproduce the experimental values with essentially the same root-mean-square (rms) error of about 1.3 Hz, regardless of the basis set used. These discrepancies could be in part due to a considerable impact of rovibrational effects on the observed J(HH) couplings, since the latter show a measurable dependence on temperature. Because of the lasting literature controversies concerning the symmetry of parent compound 1, D(2h) versus D(2), a critical analysis of the relevant literature data is carried out. The symmetry issue is prone to confusion because, according to some literature claims, the two hypothetical enantiomeric D(2) structures of 1 could be separated by a very low energy barrier that would explain the occurrence of rovibrational effects on the observed vicinal J(HH) couplings. However, the D(2h) symmetry of 1 with a flat energy minimum could also account for these effects. 相似文献
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