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Triplet Ground State (triplet + ground_state)
Selected AbstractsA Spiro-Fused Triarylaminium Radical Cation with a Triplet Ground State,ANGEWANDTE CHEMIE, Issue 32 2009Akihiro Ito Dr. No abstract is available for this article. [source] Ligand Effects on the Mechanisms of Thermal Bond Activation in the Gas-Phase Reactions NiX+/CH4,Ni(CH3)+/HX (X=H, CH3, OH, F).HELVETICA CHIMICA ACTA, Issue 12 2008Short Communication Abstract The thermal ion-molecule reactions NiX++CH4,Ni(CH3)++HX (X=H, CH3, OH, F) have been studied by mass spectrometric methods, and the experimental data are complemented by density functional theory (DFT)-based computations. With regard to mechanistic aspects, a rather coherent picture emerges such that, for none of the systems studied, oxidative addition/reductive elimination pathways are involved. Rather, the energetically most favored variant corresponds to a , -complex-assisted metathesis (, -CAM). For X=H and CH3, the ligand exchange follows a ,two-state reactivity (TSR)' scenario such that, in the course of the thermal reaction, a twofold spin inversion, i.e., triplet,singlet,triplet, is involved. This TSR feature bypasses the energetically high-lying transition state of the adiabatic ground-state triplet surface. In contrast, for X=F, the exothermic ligand exchange proceeds adiabatically on the triplet ground state, and some arguments are proposed to account for the different behavior of NiX+/Ni(CH3)+ (X=H, CH3) vs. NiF+. While the couple Ni(OH)+/CH4 does not undergo a thermal ligand switch, the DFT computations suggest a potential-energy surface that is mechanistically comparable to the NiF+/CH4 system. Obviously, the ligands X act as a mechanistic distributor to switch between single vs. two-state reactivity patterns. [source] Extended Hartree,Fock theory of chemical reactions.INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008VIII. Abstract We have investigated the reaction pathways for the primary hydroxylation reaction of trimethylmethane by a high-valent Fe(IV)O porphyrin ,-cation radical species known as compound I at the B3LYP/CEP-31G level. The isoelectronic analogy of the Fe(IV)O core of compound I to a molecular oxygen (O2) has been successfully used to clarify the important roles of the singlet excited state of the Fe(IV)O core in the alkane hydroxylation, which has hitherto been neglected. The reaction is initiated by the rate-determining hydrogen-atom abstraction from the substrate to give a discrete radical intermediate complex, in accordance with the conventional radical rebound mechanism. Similar to the chemistry of O2, however, one of the singlet excited states, i.e., the diradical component of the 1, state of the Fe(IV)O core intercepts the triplet ground state (the 3, state) in the region of the transition state for the hydrogen abstraction. Our findings strongly indicate that the exchange polarization or intersystem crossing for the nonradiative transition to the locally singlet state is highly important to enhance the reactivity of compound I. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] The Reaction of Ozone with the Hydroxide Ion: Mechanistic Considerations Based on Thermokinetic and Quantum Chemical Calculations and the Role of HO4, in Superoxide DismutationCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2010Gábor Merényi Prof. Abstract The reaction of OH, with O3 eventually leads to the formation of . OH radicals. In the original mechanistic concept (J. Staehelin, J. Hoigné, Environ. Sci. Technol.1982, 16, 676,681), it was suggested that the first step occurred by O transfer: OH,+O3,HO2,+O2 and that . OH was generated in the subsequent reaction(s) of HO2, with O3 (the peroxone process). This mechanistic concept has now been revised on the basis of thermokinetic and quantum chemical calculations. A one-step O transfer such as that mentioned above would require the release of O2 in its excited singlet state (1O2, O2(1,g)); this state lies 95.5,kJ,mol,1 above the triplet ground state (3O2, O2(3,g,)). The low experimental rate constant of 70,M,1,s,1 is not incompatible with such a reaction. However, according to our calculations, the reaction of OH, with O3 to form an adduct (OH,+O3,HO4,; ,G=3.5,kJ,mol,1) is a much better candidate for the rate-determining step as compared with the significantly more endergonic O transfer (,G=26.7,kJ,mol,1). Hence, we favor this reaction; all the more so as numerous precedents of similar ozone adduct formation are known in the literature. Three potential decay routes of the adduct HO4, have been probed: HO4,,HO2,+1O2 is spin allowed, but markedly endergonic (,G=23.2,kJ,mol,1). HO4,,HO2,+3O2 is spin forbidden (,G=,73.3,kJ,mol,1). The decay into radicals, HO4,,HO2.+O2.,, is spin allowed and less endergonic (,G=14.8,kJ,mol,1) than HO4,,HO2,+1O2. It is thus HO4,,HO2.+O2., by which HO4, decays. It is noted that a large contribution of the reverse of this reaction, HO2.+O2.,,HO4,, followed by HO4,,HO2,+3O2, now explains why the measured rate of the bimolecular decay of HO2. and O2., into HO2,+O2 (k=1×108,M,1,s,1) is below diffusion controlled. Because k for the process HO4,,HO2.+O2., is much larger than k for the reverse of OH,+O3,HO4,, the forward reaction OH,+O3,HO4, is practically irreversible. [source] Reactions of Th and U Atoms with C2H2: Infrared Spectra and Relativistic Calculations of the Metallacyclopropene, Actinide Insertion, and Ethynyl ProductsCHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2006Lester Andrews Prof. Dr. Abstract Reactions of laser-ablated Th and U atoms with C2H2 during condensation with excess argon at 7 K give several new product species. The metallacyclopropene, inserted hydride, and actinide ethynyl are identified from isotopic frequencies and relativistic DFT calculations. The higher-energy vinylidine isomer was not observed. These actinide metallacyclopropenes exhibit substantially stronger bonding interactions than found recently for the Pd and Pt metals. In the case of Th(C2H2) the argon matrix interaction is strong enough to reverse the computed order of states (MR-CISD) in favor of a triplet ground state for the (Ar)n(Th(C2H2)) complex. The nature of the electronic interactions between various metal atoms and acetylene is compared and the origin of the particularly strong interaction for U and Th is traced to the higher energy of their 6d orbitals. The ThCCH and UCCH actinide ethynyl products are also observed and characterized by CC stretching modes 38±2 cm,1 lower than acetylene itself. [source] Experimental and Theoretical Characterization of a Triplet Boron Carbonyl Compound: BBCOCHEMPHYSCHEM, Issue 7 2003Mingfei Zhou Prof. Unusually generous donation: Matrix isolation infrared spectroscopy and quantum chemical calculations characterize the new boron carbonyl compound BBCO (see graphic), which has a linear triplet ground state (3,,). The binding energy of CO and BB is quite large, due to the back bonding usually associated with transition metal carbonyl complexes. [source] | ||||||||||