共查询到20条相似文献,搜索用时 15 毫秒
1.
Dr. Beni B. Dangi Dr. Dorian S. N. Parker Dr. Tao Yang Prof. Ralf I. Kaiser Prof. Alexander M. Mebel 《Angewandte Chemie (International ed. in English)》2014,53(18):4608-4613
Dicarbon (C2), the simplest bare carbon molecule, is ubiquitous in the interstellar medium and in combustion flames. A gas‐phase synthesis is presented of the benzyl radical (C6H5CH2) by the crossed molecular beam reaction of dicarbon, C2(X1Σg+, a3Πu), with 2‐methyl‐1,3‐butadiene (isoprene; C5H8; X1A′) accessing the triplet and singlet C7H8 potential energy surfaces (PESs) under single collision conditions. The experimental data combined with ab initio and statistical calculations reveal the underlying reaction mechanism and chemical dynamics. On the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the barrierless addition of dicarbon to the carbon–carbon double bond of the 2‐methyl‐1,3‐butadiene molecule. These initial addition complexes rearrange via multiple isomerization steps, leading eventually to the formation of C7H7 radical species through atomic hydrogen elimination. The benzyl radical (C6H5CH2), the thermodynamically most stable C7H7 isomer, is determined as the major product. 相似文献
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Dr. Daniel Himmel Dipl.‐Chem. Sascha K. Goll Prof. Dr. Ivo Leito Prof. Dr. Ingo Krossing 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(30):9333-9340
The capability of a gaseous Brønsted acid HB to deliver protons to a base is usually described by the gas‐phase acidity (GA) value of the acid. However, GA values are standard Gibbs energy differences and refer to individual gas pressures of 1 bar for acid HB, base B?, and proton H+. We show that the GA value is not suited to describe the bulk acidity of a gaseous acid. Here the pressure dependence of the activities of HB, H(HB)n+, and B(HB)m? that result from gaseous autoprotolysis have to be considered. In this work, the pressure‐dependent absolute chemical potential of the proton in the representative gaseous proton acids CH4, NH3, H2O, HF, and HCl was worked out and the general theory to describe bulk gas phase acidity—that can directly be compared with solution acidity—was developed. 相似文献
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Mechanistic Aspects of the Gas‐Phase Reactions of Halobenzenes with Bare Lanthanide Cations: A Combined Experimental/Theoretical Investigation 下载免费PDF全文
Dr. Shaodong Zhou Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(5):2123-2131
The gas‐phase reactions of chlorobenzene with all atomic lanthanide cations Ln+ (except Pm+) have been investigated by using Fourier transform ion cyclotron resonance mass spectrometry in conjunction with density functional theory calculations. According to the latter, a direct chlorine transfer to the lanthanide cation, which has been observed previously for fluorine abstraction from fluorobenzene, is not operative for the C6H5Cl/Ln+ couples; rather, chlorine transfer proceeds through an initial coordination of the lanthanide cation to the aromatic ring of the substrate. Both, the product distribution and the chlorine abstraction efficiencies are affected by the bond dissociation energy (BDE(Ln+?Cl)) as well as the promotion energies of Ln+ to attain a 4fn 5d1 6s1 configuration. In addition, mechanistic aspects of some C?H and C?C bond activations are presented. Where appropriate, comparison with the previously studied C6H5F/Ln+ systems is made. 相似文献
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Molecular Salt Effects in the Gas Phase: Tuning the Kinetic Basicity of [HCCLiCl]− and [HCCMgCl2]− by LiCl and MgCl2 下载免费PDF全文
Dr. George N. Khairallah Dr. Gabriel da Silva Prof. Richard A. J. O'Hair 《Angewandte Chemie (International ed. in English)》2014,53(41):10979-10983
A combination of gas‐phase ion–molecule reaction experiments and theoretical kinetic modeling is used to examine how a salt can influence the kinetic basicity of organometallates reacting with water. [HC?CLiCl]? reacts with water more rapidly than [HC?CMgCl2]?, consistent with the higher reactivity of organolithium versus organomagnesium reagents. Addition of LiCl to [HC?CLiCl]? or [HC?CMgCl2]? enhances their reactivity towards water by a factor of about 2, while addition of MgCl2 to [HC?CMgCl2]? enhances its reactivity by a factor of about 4. Ab initio calculations coupled with master equation/RRKM theory kinetic modeling show that these reactions proceed via a mechanism involving formation of a water adduct followed by rearrangement, proton transfer, and acetylene elimination as either discrete or concerted steps. Both the energy and entropy requirements for these elementary steps need to be considered in order to explain the observed kinetics. 相似文献
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Latifa Latrous Jeanine Tortajada Violette Haldys Emmanuelle Léon Catarina Correia Jean‐Yves Salpin 《Journal of mass spectrometry : JMS》2013,48(7):795-806
Gas‐phase interactions of organotins with glycine have been studied by combining mass spectrometry experiments and quantum calculations. Positive‐ion electrospray spectra show that the interaction of di‐ and tri‐organotins with glycine results in the formation of [(R)2Sn(Gly)‐H]+and [(R)3Sn(Gly)]+ ions, respectively. Di‐organotin complexes appear much more reactive than those involving tri‐organotins. (MS/MS) spectra of the [(R)3Sn(Gly)]+ ions are indeed simple and only show elimination of intact glycine, generating the [(R)3Sn]+ carbocation. On the other hand, MS/MS spectra of [(R)2Sn(Gly)‐H]+complexes are characterized by numerous fragmentation processes. Six of them, associated with elimination of H2O, CO, H2O + CO and formation of [(R)2SnOH]+ (?57 u),[(R)2SnNH2]+( ?58 u) and [(R)2SnH]+ (?73 u), are systematically observed. Use of labeled glycines notably concludes that the hydrogen atoms eliminated in water and H2O + CO are labile hydrogens. A similar conclusion can be made for hydrogens of [(R2)SnOH]+and [(R2)SnNH2]+ions. Interestingly, formation [(R)2SnH]+ ions is characterized by a migration of one the α hydrogen of glycine onto the metallic center. Finally, several dissociation routes are observed and are characteristic of a given organic substituent. Calculations indicated that the interaction between organotins and glycine is mostly electrostatic. For [(R)2Sn(Gly)‐H]+complexes, a preferable bidentate interaction of the type η2‐O,NH2 is observed, similar to that encountered for other metal ions. [(R)3Sn]+ ions strongly stabilize the zwitterionic form of glycine, which is practically degenerate with respect to neutral glycine. In addition, the interconversion between both forms is almost barrierless. Suitable mechanisms are proposed in order to account for the most relevant fragmentation processes. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Latifa Latrous Jean‐Yves Salpin Violette Haldys Emmanuelle Léon Catarina Correia Al Mokhtar Lamsabhi 《Journal of mass spectrometry : JMS》2016,51(11):1006-1015
The gas‐phase interactions of cysteine with di‐organotin and tri‐organotin compounds have been studied by mass spectrometry experiments and quantum calculations. Positive‐ion electrospray spectra show that the interaction of di‐ and tri‐organotins with cysteine results in the formation of [(R)2Sn(Cys‐H)]+ and [(R)3Sn(Cys)]+ ions, respectively. MS/MS spectra of [(R)2Sn(Cys‐H)]+ complexes are characterized by numerous fragmentation processes, notably associated with elimination of NH3 and (C,H2,O2). Several dissociation routes are characteristic of each given organic species. Upon collision, both the [(R)3Sn(Gly)]+ and [(R)3Sn(Cys)]+ complexes are associated with elimination of the intact amino acid, leading to the formation of [(R)3Sn]+ cation. But for the latter complex, two additional fragmentation processes are observed, associated with the elimination of NH3 and C3H4O2S. Calculations indicate that the interaction between organotins and cysteine is predominantly electrostatic but also exhibits a considerable covalent character, which is slightly more pronounced in tri‐organotin complexes. A preferred bidentate interaction of the type ‐η2‐S‐NH2, with sulfur and the amino group, is observed. As for the [(R)3Sn(Cys)]+ complexes, their stability is due to the combination of the hydrogen bond taking place between the amino group and the sulfur lone pair and the interaction between the carboxylic oxygen atom and the metal. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Inside Back Cover: Molecular Salt Effects in the Gas Phase: Tuning the Kinetic Basicity of [HCCLiCl]− and [HCCMgCl2]− by LiCl and MgCl2 (Angew. Chem. Int. Ed. 41/2014) 下载免费PDF全文
Dr. George N. Khairallah Dr. Gabriel da Silva Prof. Richard A. J. O'Hair 《Angewandte Chemie (International ed. in English)》2014,53(41):11097-11097
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Dr. Gerald Knizia Dr. Johannes E. M. N. Klein 《Angewandte Chemie (International ed. in English)》2015,54(18):5518-5522
The “curly arrow” of Robinson and Ingold is the primary tool for describing and rationalizing reaction mechanisms. Despite this approach’s ubiquity and stellar success, its physical basis has never been clarified and a direct connection to quantum chemistry has never been found. Here we report that the bond rearrangements expressed by curly arrows can be directly observed in ab initio computations, as transformations of intrinsic bond orbitals (IBOs) along the reaction coordinate. Our results clarify that curly arrows are rooted in physical reality—a notion which has been challenged before—and show how quantum chemistry can directly establish reaction mechanisms in intuitive terms and unprecedented detail. 相似文献
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Dr Dorian S. N. Parker Dr Fangtong Zhang Dr Ralf I. Kaiser Dr Vadim V. Kislov Dr Alexander M. Mebel 《化学:亚洲杂志》2011,6(11):3035-3047
Polycyclic aromatic hydrocarbons (PAHs) are regarded as key intermediates in the molecular growth process that forms soot from incomplete fossil fuel combustion. Although heavily researched, the reaction mechanisms for PAH formation have only been investigated through bulk experiments; therefore, current models remain conjectural. We report the first observation of a directed synthesis of a PAH under single‐collision conditions. By using a crossed‐molecular‐beam apparatus, phenyl radicals react with C3H4 isomers, methylacetylene and allene, to form indene at collision energies of 45 kJ mol?1. The reaction dynamics supported by theoretical calculations show that both isomers decay through the same collision complex, are indirect, have long lifetimes, and form indene in high yields. Through the use of deuterium‐substituted reactants, we were able to identify the reaction pathway to indene. 相似文献
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Density functional theory has become a valuable tool to study surface catalysis. However, due to the scarcity of clean and reliable experimental data on surfaces, the theoretical methods employed to explore heterogeneous catalytic mechanisms are usually less well validated than those for gas‐phase reactions. We argue herein that gas‐phase reactions and the corresponding surface reactions are related through the Born–Haber cycle and computational catalysis on surfaces will be less meaningful if gas‐phase behavior cannot first be suitably determined. In this contribution, we have constructed a set of gas‐phase reactions relevant to the Fischer–Tropsch synthesis as a case study. With this set, we have tested the validity of the widely used PBE and B3LYP functionals and found that neither of them are capable of describing all kinds of gas‐phase reactions properly, such that some surface reactions may be biased falsely against the others. Significantly, XYG3, which is a double‐hybrid functional that includes Hartree–Fock‐like exchange and many‐body perturbation correlation effects, presents a significant improvement for all of the gas‐phase reactions, holding promise for further development for surface catalysis. 相似文献
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Aaron M. Thomas Long Zhao Chao He Galiya R. Galimova Alexander M. Mebel Ralf I. Kaiser 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(43):15634-15641
The triafulvene molecule (c‐C4H4)—the simplest representative of the fulvene family—has been synthesized for the first time in the gas phase through the reaction of the methylidyne radical (CH) with methylacetylene (CH3CCH) and allene (H2CCCH2) under single‐collision conditions. The experimental and computational data suggest triafulvene is formed by the barrierless cycloaddition of the methylidyne radical to the π‐electron density of either C3H4 isomer followed by unimolecular decomposition through elimination of atomic hydrogen from the CH3 or CH2 groups of the reactants. The dipole moment of triafulvene of 1.90 D suggests that this molecule could represent a critical tracer of microwave‐inactive allene in cold molecular clouds, thus defining constraints on the largely elusive hydrocarbon chemistry in low‐temperature interstellar environments, such as that of the Taurus Molecular Cloud 1 (TMC‐1). 相似文献
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Pseudo‐Contact NMR Shifts over the Paramagnetic Metalloprotein CoMMP‐12 from First Principles 下载免费PDF全文
Dr. Ladislav Benda Dr. Jiří Mareš Dr. Enrico Ravera Prof. Dr. Giacomo Parigi Prof. Dr. Claudio Luchinat Prof. Dr. Martin Kaupp Prof. Dr. Juha Vaara 《Angewandte Chemie (International ed. in English)》2016,55(47):14713-14717
Long‐range pseudo‐contact NMR shifts (PCSs) provide important restraints for the structure refinement of proteins when a paramagnetic metal center is present, either naturally or introduced artificially. Here we show that ab initio quantum‐chemical methods and a modern version of the Kurland–McGarvey approach for paramagnetic NMR (pNMR) shifts in the presence of zero‐field splitting (ZFS) together provide accurate predictions of all PCSs in a metalloprotein (high‐spin cobalt‐substituted MMP‐12 as a test case). Computations of 314 13C PCSs using g‐ and ZFS tensors based on multi‐reference methods provide a reliable bridge between EPR‐parameter‐ and susceptibility‐based pNMR formalisms. Due to the high sensitivity of PCSs to even small structural differences, local structures based either on X‐ray diffraction or on various DFT optimizations could be evaluated critically by comparing computed and experimental PCSs. Many DFT functionals provide insufficiently accurate structures. We also found the available 1RMZ PDB X‐ray structure to exhibit deficiencies related to binding of a hydroxamate inhibitor. This has led to a newly refined PDB structure for MMP‐12 (5LAB) that provides a more accurate coordination arrangement and PCSs. 相似文献
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Dr. George N. Khairallah Dr. Alan T. Maccarone Dr. Huong T. Pham Timothy M. Benton Dr. Tony Ly Dr. Gabriel da Silva Prof. Stephen J. Blanksby Prof. Richard A. J. O'Hair 《Angewandte Chemie (International ed. in English)》2015,54(44):12947-12951
Although the deleterious effects of ozone on the human respiratory system are well‐known, many of the precise chemical mechanisms that both cause damage and afford protection in the pulmonary epithelial lining fluid are poorly understood. As a key first step to elucidating the intrinsic reactivity of ozone with proteins, its reactions with deprotonated cysteine [Cys?H]? are examined in the gas phase. Reaction proceeds at near the collision limit to give a rich set of products including 1) sequential oxygen atom abstraction reactions to yield cysteine sulfenate, sulfinate and sulfonate anions, and significantly 2) sulfenate radical anions formed by ejection of a hydroperoxy radical. The free‐radical pathway occurs only when both thiol and carboxylate moieties are available, implicating electron‐transfer as a key step in this reaction. This novel and facile reaction is also observed in small cys‐containing peptides indicating a possible role for this chemistry in protein ozonolysis. 相似文献
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《Chemphyschem》2003,4(1):72-78
The Cu+ and Ni+ binding energies of ethynylamine, ethynylphosphine and ethynylarsine have been calculated at the B3LYP/6‐311+G(2df,2p)//B3LYP/6‐311G(d,p) level of theory. Significant differences between nitrogen‐containing and phosphorus‐ or arsenic‐containing compounds have been found regarding structural effects upon metal cation association. While for ethynylamine the global minimum of the potential energy surface corresponds to the complex in which the metal cation binds to the β‐carbon, for ethynylphosphine the most favourable process corresponds to phosphorus attachment. For ethynylarsine, the conventional π‐complex is the most stable one. This behavior resembles that found for the corresponding vinyl analogues, with the only exception being the arsenic derivative. The calculated Cu+ and Ni+ binding energies for attachment to the heteroatom follow a different trend, P>As>N, to that predicted for the corresponding proton affinities, P>N>As. Cu+ and Ni+ binding energies are almost identical when the metal cation binds to the heteroatom. However, Ni+ binding energies are slightly larger than Cu+ binding energies when the metal cation interacts with the C?C bond. 相似文献