Theoretical Study (theoretical + study)

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Theoretical Study

  • comprehensive theoretical study

  • Selected Abstracts

    Ruthenium-to-Platinum Interactions in ,6,,1 NCN-Pincer Arene Heterobimetallic Complexes: An Experimental and Theoretical Study

    Sylvestre Bonnet
    Abstract A series of ,6,,1 -heterobimetallic complexes have been prepared in which a [Ru(,6 -arene)(C5R5)]+ fragment (R = H or Me) and an ,1 -NCN-pincer platinum fragment are combined within the same molecule. In complexes [2]+ and [3]+, the ruthenium and platinum centers are ,6 and ,1 coordinated, respectively, to the same arene ring, whereas in [4A]+ and [5A]+ they are coordinated to two different arene rings that are linked with a covalent bond ([4A]+) or an ethyl bridge ([5A]+). Upon changing the organic manifold between both metal centers, very strong ([2]+) to very weak ([5A]+) ruthenium-to-platinum interactions are obtained. Experimentally, X-ray crystal structures show an increaing steric hindrance when the Ru,Pt distance diminishes, and electrochemical and 195Pt NMR spectroscopic studies show a decreasing electron density on platinum from [5A]+ to [2]+. Theoretical DFT calculations were undertaken, which show an increasing charge on platinum from [5A]+ to [2]+. Our theoretical analysis shows that the particularly strong ruthenium-to-platinum electronic interactions in [2]+ and [3]+ do not come from binding of ruthenium to platinum, but from the pincer Cipso sharing its electron density between both metal centers, which decreases the , donation to platinum, and from increased backdonation of the platinum d electrons into the , system of the arene ring. [source]

    A Theoretical Study on the Reactivity of a Rhenium Hydroxo-Carbonyl Complex Towards ,-Lactams

    Violeta Yeguas
    Abstract The mechanism of the reaction between the complex [Re(OH)(CO)3(N2C2H4)] and azetidin-2-one or 3-formylamino- N -sulfonatoazetidin-2-one was investigated by using the B3LYP density functional theory methodology in conjunction with the PCM-UAHF model to take into account solvent effects. According to our calculations, the rate-determining energy barrier for the azetidin-2-one case of 38.8 kcal,mol,1, becomes 25.7 kcal,mol,1 in the case of the 3-formylamino- N -sulfonatoazetidin-2-one species. The presence of the sulfonato group is crucial for the cleavage of the ,-lactam N1,C2 bond by the Re complex thanks to the interaction of the sulfonato group with the hydroxy and bidentate ligands of the complex. This could be of interest for the synthesis of ,-amino acids and their derivatives from ,-lactams under mild conditions and in solvents of low polarity promoted by organometallic complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Mechanistic Insights into Acetophenone Transfer Hydrogenation Catalyzed by Half-Sandwich Ruthenium(II) Complexes Containing 2-(Diphenylphosphanyl)aniline , A Combined Experimental and Theoretical Study

    Alessia Bacchi
    Abstract Several new half-sandwich ruthenium(II) complexes containing 2-(diphenyphosphanyl)aniline (PNH2) of formula {Ru[(,2P,N)PNH2](p -cymene)Cl}Y [Y = Cl (1a), PF6 (1b), BF4 (1c), BPh4 (1d), TfO (1e)] were synthesized and fully characterized both in solution (1H NMR and 31P{1H} NMR spectroscopy) and in the solid state (FTIR, X-ray analysis on single crystal). Complexes 1a and 1b are active precatalysts in the hydrogen transfer reaction of acetophenone, leading to tof values up to 4440 h,1. In comparison, the {Ru[(,2P,N)PNMe2](p -cymene)Cl}Cl complex leads to a tof value of 100 h,1 under the same catalytic conditions. The mechanism through which the precatalysts operate was deeply explored by high-resolution MS (ESI) and DFT/PCM studies. The results reveal that the complexes containing PNH2 operate through a bifunctional mechanism analogous to that proposed for diamines and amino alcohol ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Theoretical Study on a Class of Organometallic Complexes Based on All-Metal Aromatic Ga3, Through Sandwiching Stabilization

    Li-ming Yang
    Abstract We report the theoretical study on a class of organometallic complexes containing the all-metal aromatic unit Ga3, on the basis of density functional theory calculations on a series of model sandwich-like compounds [DM(Ga3)]q, as well as those of the saturated compounds [DMn(Ga3)] [D = Ga3,, Cp,(C5H5,); M = Li, Na, K, Be, Mg, Ca] and extended compounds (Cp,)m(Li+)n(Ga3,)o (m, n, and o are integers). For the six metals, the all-metal aromatic Ga3, can only be assembled and stabilized in the "heterodecked sandwich" scheme (e.g. [CpM(Ga3)]q,) so as to avoid cluster fusion. Moreover, we designed a novel class of all-metal aromatic "metalloid" compounds. The ground state heterodecked sandwich species (Cp),(M)q+(Ga3), (M = Li, Na, K, q = 1; M = Be, Mg, Ca, q = 2) and the extended sandwich species (Cp,)m(Li+)n(Ga3,)o are mainly ionic bonded, cluster-assembled "polyatomic molecule", grown from the combination of Cp,, M atoms, and Ga3,. As a prototype for ionic bonding involving intact Ga3, subunits, [CpM(Ga3)]q, may be a stepping stone toward forming ionic, cluster-assembled all-metal aromatic Ga3 -based bulk solids or materials. Additionally, our results for the first time showed that the electronic, structural, and aromatic properties of the all-metal aromatic Ga3, could be well retained during cluster assembly, which is indicative of "building block" character. Bearing the significant difference in bonding patterns between our designed metalloid compounds and the known metalloid species, synthesis of these novel species might present an attractive challenge to experimental chemists. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    A Theoretical Study of the Nearest Cu···Cu Antiferromagnetic Exchange Coupling Interactions in [LaCu6] and [YCu6]

    Yi-Quan Zhang
    Abstract A density functional study of the exchange coupling interactions between the two nearest CuII centers in [LaCu6] and [YCu6] is presented. Two approaches show that the Cu···Cu antiferromagnetic interactions increase with a decrease of the ionic radius of the diamagnetic central LaIII and YIII ions. However, the influence of the central ions on the Cu···Cu interactions is small compared to that of their structures according to our calculations. We therefore conclude that the stronger antiferromagnetic interactions between the two nearest CuII centers in [LaCu6] than in [YCu6] are not a result of the central LaIII ion but the structure. The antiferromagnetic contributions of the direct overlap between the two nearest CuII magnetic orbitals also play a major role according to the calculations of the overlap integral Sij based on Kahn's theory.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    A Theoretical Study of the Exchange Coupling in Hydroxo- and Alkoxo-Bridged Dinuclear Oxovanadium(IV) Compounds

    Antonio Rodríguez-Fortea
    Abstract A density functional study of exchange coupling in hydroxo- and alkoxo-bridged dinuclear oxovanadium(IV) compounds is presented. Coupling constants calculated for full unmodeled structures are in good agreement with experimentally reported values, confirming the ability of the computational strategy used in this work to predict the exchange coupling in dinuclear VIV compounds. The influence of the configuration of the [VO(,-OR)2VO]2+ core in compounds with two edge-sharing octahedrally coordinated oxovanadium(IV) centers, of the nature of the terminal ligands and of structural distortions on the coupling constant have been analyzed through model calculations. The results indicate that the coupling constant is less affected by these factors than for hydroxo- and alkoxo-bridged CuII compounds. The calculations support the orbital models usually employed in qualitative interpretations of magneto-structural correlations, showing good correlations between the calculated coupling constants and the overlap between the two magnetic orbitals or the square of the orbital gap. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Photochemistry of Salicylaldoxime in Solid Argon: An Experimental and Theoretical Study

    Joanna Grzegorzek
    Abstract The photochemistry of salicylaldoxime in solid argon has been investigated by FTIR spectroscopy and DFT calculations. The salicylaldoxime molecule trapped in the matrix from the vapor above the solid sample has the most stable syn1 conformation with an intramolecular hydrogen bond. Irradiation (, > 320 nm) leads to conversion of the syn1 conformer into the syn3 one, in which the C(H)NOH and (C)OH groups are rotated around the C,C and C,O bonds, respectively, and the intramolecular hydrogen bond is broken. The photochemistry of syn3 involves three possible routes: (i) conversion of syn3 into anti2 conformer, this process requires rearrangement of the NOH group with respect to the C=N bond; (ii) photodissociation of salicylaldoxime into 2-cyanophenol and water, which form a hydrogen-bonded complex; and (iii) regeneration of the syn1 conformer. The third route is a very small contribution to the overall process. The study performed with [D2]salicylaldoxime indicates that the dehydration reaction of salicylaldoxime involves cleavage of the N,O bond and formation of OH and Ph(OH)C(H)N radicals in the first step. Then, the OH radical abstracts a hydrogen atom from the CH group to form 2-cyanophenol and water molecules. When the sample is exposed to the full output of the mercury lamp the 2-cyanophenol complex with water becomes the dominating product. [source]

    Theoretical Study on Hetero-Diels,Alder Reaction of Butadiene with Benzaldehyde Catalyzed by Chiral InIII Complexes

    Xiuli Cao
    Abstract The mechanism of the hetero-Diels,Alder reaction of butadiene with benzaldehyde catalyzed by chiral N,N, -dioxide/In(OTf)3 complexes was studied theoretically by using density functional theory (DFT) and model system. The computational results indicate that the catalyzed reaction proceeded through a concerted mechanism via a highly zwitterionic transition state. The lowest energy barrier was 11.8 kJ,mol,1, which is 63.0 kJ,mol,1 lower than that of the uncatalyzed reaction. The results indicate that the endo approach is advantageous over the exo approach, because exo transitions states suffer from more steric hindrance than the endo transitions states as a result of interactions among the substrates, the trifluoromethanesulfonic group and the R4 groups of the ligand. The (S) configuration was observed predominantly over the (R) form, because there is no distinguishable repulsion between butadiene and the exo amino side or the endo amino side of the ligand. Besides, the interactions between the terminal hydrogen atoms of butadiene and the oxygen atoms of the trifluoromethanesulfonic group make the structure more stable. Thus, the experimental results were explained well by calculation of the chiral N,N, -dioxide/In(OTf)3 complex catalyzed hetero-Diels,Alder reaction at the molecular level. [source]

    Synthetic and Mechanistic Aspects of Acid-Catalyzed Disproportionation of Dialkyl Diarylmethyl Ethers: A Combined Experimental and Theoretical Study

    Margherita Barbero
    Abstract The disproportionation reactions of various dialkyl diarylmethyl ethers have been carried out in the presence of a catalytic amount (10 mol-%) of o -benzenedisulfonimide as a Brønsted acid catalyst; the reaction conditions were mild, and the yields of the diarylmethane target products were good. The catalyst was easily recovered and purified, ready to be used in further reactions. The theoretical study confirmed that the reaction proceeds in two steps: The formation of a carbocation from the protonated ether followed by hydride transfer. Although the hydride transfer is the rate-determining step, it is the stability of the carbocation that determines the reaction rate and therefore the yields. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Diels,Alder Reactions of Symmetrically 1,4-Disubstituted Dienes: Theoretical Study on the Influence of the Configuration of the Double Bonds on the Regio- and Endoselectivity

    Samira Baki
    Abstract It was experimentally shown in Diels-Alder reactions that symmetrically 1,4-disubstituted dienes exhibit high regio- and endoselectivity induced by the (E,Z) configuration of the double bonds. In order to understand the origin of this selectivity, the transition states associated with the reaction between a series of such dienes (R = OMe, CH3, NH2, F, CN) on substituted ethylene (R, = CO2Me, CN, F, OMe) were determined by DFT calculations. If the regioselectivity confirmed by a single-point MP2 calculation is predicted to be good in most cases, its direction remains difficult to predict; the R, group of the dienophile can orient itself toward either the (Z) or the (E) side of the diene. Neither primary nor secondary frontier orbital interactions appear to be able to rationalize these results. They are more likely explained by a delicate balance between steric and electrostatic interactions. This hypothesis is further supported by the calculated reactivity of the (E,E) and (Z,Z) corresponding dienes. In any case, a standard DFT calculation, confirmed by a single-point MP2 step, is likely to provide a reliable guideline for a synthesis strategy that allows the control of up to four stereogenic centres in a single reaction step.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    A Combined Experimental and Theoretical Study of Anion,, Interactions in Bis(pyr­imidine) Salts

    Angel Garcia-Raso
    Abstract We report the synthesis and X-ray characterization of an N,N, -tetramethylenebis(2-aminopyrimidinium) tetrafluoroborate salt that exhibits anion,, interactions that are responsible for the crystal packing. The anion forms a sandwich complex with two pyrimidine rings. When the anion is nitrate, the crystal packing is governed by anion,, interactions and hydrogen bonds, and the sandwich complex is not formed. Finally, a theoretical study of the anion,, interactions in charged pyrimidine rings is in good agreement with the experimental findings. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    The Tautomerism of 5-Amino-3-oxo-1,2,4-thiadiazole: An Experimental and Theoretical Study

    Arantxa Encinas
    Abstract The 1,2,4-thiadiazole system was the subject of our research as a consequence of the pharmacological activity of some derivatives as GSK3 inhibitors. Therefore, in order to explore the active form responsible for receptor interaction, a systematic study of the tautomerism in the 5-amino-3-oxo-1,2,4-thiadiazole system was performed by using experimental and theoretical methods. Thus, the relative stability of the possible tautomers was studied in the gas phase by density functional theory and local density functional methods. The theoretical study in solution was carried out by using severalcontinuum solvation models. Finally, experimental studies were carried out to unambiguously establish the tautomeric form.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Alternative Mechanistic Paths in the Hetero-Diels,Alder Reaction of ,-Oxothiones: A Theoretical Study

    Laura Legnani
    Abstract DFT calculations at the B3LYP/6-311+G(d,p) level for the C, H, and O atoms and at the 6-311+G(2df,p) level for the S atom were used to study the hetero-Diels,Alder reactions between several ,-oxothiones and ethylene or methyl vinyl ether (MVE). All the transition states and the intermediates along the reaction pathways, as well as the reaction products, were located. The reactions with ethylene are all concerted though asynchronous whereas in the reactions with MVE the electron-releasing character of the methoxy substituent lowers the energy barriers and enhances the asynchronicity and the charge transfer process to such an extent that the reaction may become unconcerted and exhibit a two-step mechanism with a zwitterionic intermediate derived from nucleophilic attack of electron-rich MVE to the sulfur atom of the strongly electrophilically activated ,-oxothiones. The reactions are also favored by the conjugation of the newly formed C=C bond. Moreover, the geometric features of the diene exert a nonnegligible role, as dienes that are planar or almost planar in their ground state show a lower energy barrier. Thus, both geometric and electronic features of the dienes as well as of the dienophiles play a significant role in the easiness of the reactions and in their mechanism. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Preparation, Crystallographic Characterization, and Theoretical Study of C70(CF3)14,

    Alexey A. Goryunkov
    Abstract Five C70(CF3)14 isomers have been isolated chromatographically from the mixture produced in the ampoule reaction between C70 and CF3I at 390 °C. Molecular structures of four isomers have been determined in a single-crystal X-ray diffraction study. A quantum chemical survey of the theoretically possible isomers demonstrated that the structures obtained are energetically favorable but that there is probably no full thermodynamic control in the trifluoromethylation process.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    The Experimental and Theoretical Study of Phase Equilibria in the Pd,Zn (-Sn) System,

    J. Vizdal
    The binary Pd-Zn system was assessed in the scope of this paper. The experimental data from the literature were used for the assessment, together with our own data obtained by SEM-EDS analysis and by the DTA. The paper is focused particularly on the Pd-Zn system, but the Pd-Sn and Sn-Zn systems are also analysed in this paper. Finally, first prediction of the isothermal sections of the ternary Pd-Sn-Zn system was made. [source]

    A Theoretical Study of Correlation between Hydrogen-Bond Stability and J -Coupling through a Hydrogen Bond

    Shun-ichi Kawahara
    trans -Hydrogen-bond hyperfine splitting via magnetic interaction, which is observed as J -coupling in NMR experiments, was theoretically studied. trans -Hydrogen-bond hyperfine splitting should be closely related to the orbital interaction between the lone-pair orbital of the H-bond acceptor and the antibond orbital of the H-bond donor. A linear relationship was observed between magnetic interaction hyperfine splitting through a H-bond and the H-bond strength. The relationship was dependent on the type of the nucleus forming the H-bond; linear correlation was observed in NH,,,O/N type or OH,,,N type H-bonded complexes, but not in OH,,,O type H-bonded complexes. [source]

    Modification of the Surface Properties of Indium Tin Oxide with Benzylphosphonic Acids: A Joint Experimental and Theoretical Study

    ADVANCED MATERIALS, Issue 44 2009
    Peter J. Hotchkiss
    Benzylphosphonic acids with various fluorine substitutions are designed and synthesized. They are used to modify ITO such that the work function can be tuned over a range of 1.2 eV while keeping the surface energy relatively constant. The experimentally measured work function changes are also compared to and agree well with those estimated from DFT calculations. [source]

    Ring Expansion versus Cyclization in 4-Oxoazetidine-2- carbaldehydes Catalyzed by Molecular Iodine: Experimental and Theoretical Study in Concert

    Benito Alcaide
    Abstract Molecular iodine (10,mol%) efficiently catalyzes the ring expansion of 4-oxoazetidine-2-carbaldehydes in the presence of tert -butyldimethylsilyl cyanide, or allylic and propargylic trimethylsilanes to afford protected 5-functionalized-3,4-dihydroxypyrrolidin-2-ones with good yield and high diastereoselectivity, through a C3C4 bond cleavage of the ,-lactam nucleus. Interestingly, in contrast to the iodine-catalyzed reactions of 3-alkoxy-,-lactam aldehydes which lead to the corresponding ,-lactam derivatives (rearrangement adducts), the reactions of 3-aryloxy-,-lactam aldehydes under similar conditions gave ,-lactam-fused chromanes (cyclization adducts) as the sole products, through exclusive electrophilic aromatic substitution involving the C3 aromatic ring and the carbaldehyde. In order to support the mechanistic proposals, theoretical studies have been performed. [source]

    The Cycloaddition Reaction Between ,-Bromo Vinylketenes and Imines: A Combined Experimental and Theoretical Study

    Fides Benfatti
    Abstract The unusual behaviour of ,-bromo vinylketenes in the cycloaddition reactions with imines is described. This class of vinylketenes behaves as dienophiles in [2+2] reactions, but also displays an unusual diene reactivity in [4+2] reactions. Interestingly, the reactivity of ,-bromo vinylketenes can be modulated via a fine tuning of the substituents. For instance, a methyl group in the ,-position completely inhibits the [2+2] reaction and the [4+2] pathway is almost exclusively followed. A more hindered ketimine (instead of a simple imine) is enough to activate again the [2+2] mechanism. We have carried out a DFT theoretical investigation to rationalise these experimental observations. We have considered two pathways for the [2+2] reaction involving imine, that is, the endo and exo pathways. The former is favoured in the case of ,-bromo vinylketenes, while the latter is preferred for non-substituted vinylketenes. Since the [4+2] cycloaddition becomes possible only when the s - Z -conformation of vinylketene is significantly populated, the presence of bromine substituents in this substrate is crucial in determining the [2+2] or [4+2] mechanisms. For unsubstituted vinylketenes, the barrier connecting the s-E - to the s-Z -conformation is too high to be easily overcome. Thus, the s - Z -structure has a low population and the [2+2] mechanism is favoured. In the case of ,-bromo vinylketenes (especially the ,-methyl-substituted ones), this barrier can be surmounted and the [4+2] mechanism becomes available. [source]

    Ethylene and Propylene Polymerization Using In Situ Supported Me2Si(Ind)2ZrCl2 Catalyst: Experimental and Theoretical Study

    Fernando C. Franceschini
    Abstract Summary: Me2Si(Ind)2ZrCl2 was in situ immobilized onto SMAO and used for ethylene and propylene polymerization in the presence of TEA or TIBA as cocatalyst. The catalytic system Me2Si(Ind)2ZrCl2/SMAO exhibited different behavior depending on the amount and nature of the alkylaluminum employed and on the monomer type. The catalyst activity was nearly 0.4 kg polymer,·,g cat,1,·,h,1 with both cocatalysts for propylene polymerization. Similar activities were observed for ethylene polymerization in the presence of TIBA. When ethylene was polymerized using TEA at an Al/Zr molar ratio of 250, the activity was 10 times higher. Polyethylenes made by in situ supported or homogeneous catalyst systems had practically the same melting point (Tm). On the other hand, poly(propylenes) made using in situ supported catalyst systems had a slightly lower Tm than poly(propylenes) made using homogeneous catalyst systems. The nature and amount of the alkylaluminum also influenced the molar mass. The poly(propylene) molar mass was higher when TIBA was the cocatalyst. The opposite behavior was observed for the polyethylenes. Concerning the alkylaluminum concentration, the molar mass of the polymers decreased as the amount of TEA increased. In the presence of TIBA, the polyethylene's molar mass was almost the same, independent of the alkylaluminum concentration, and the poly(propylene) molar mass increased with increasing amounts of cocatalyst. The deconvolution of the GPC curves showed 2 peaks for the homogeneous system and 3 peaks for the heterogeneous in situ supported system. The only exception was observed when TEA was used at an Al/Zr molar ratio of 500, where the best fit was obtained with 2 peaks. Based on the GPC deconvolution results and on the theoretical modeling, a proposal for the active site structure was made. Molar mass distribution deconvolution of polyethylene prepared with the system Me2Si(Ind)2ZrCl2/SMAO/TIBA with 500 mol/mol of alkylaluminum as cocatalyst. [source]

    Superelectrophilic Activation of N -Substituted Isatins: Implications for Polymer Synthesis, a Theoretical Study

    Daniel Romero Nieto
    Abstract The stability and reactivity of mono- and multi-protonatred N -substituted isatin derivatives were studied at PBE0/aug-cc-pvtz//PBE0/6-31+G** level of theory in triflic acid (TFSA) solution. Calculations showed that the monocationic intermediates are the principal reactive species in the reaction of hydroxyalkylation of isatin derivatives in TFSA media. Electron-withdrawing substituents on the nitrogen atom increase the reactivity of isatin-containing electrophiles towards aromatic hydrocarbons, in accordance with their expected electronic influence. Steric factors also play an important role in the reactivity of isatin-containing electrophiles, especially in the second reaction step, due to their more sterically hindered reactive center. [source]

    Geometries and Electronic Structures of Co-Oligomers and Co-Polymers Based on Tricyclic Nonclassical Thiophene: A Theoretical Study

    Yangwu Fu
    Abstract The geometries and electronic properties of four copolymers based on tricyclic nonclassical thiophene were studied using DFT at the B3LYP/6-31G(d) level. Bond lengths and their alternation, electron densities at BCPs, NICS, and WBIs were analyzed and correlated with the energy gap. The results show that the degree of conjugation increases upon main chain extension. The energy gap decreased steadily with increasing degree of polymerization. Conjugation is stronger in the central than in the outer section. The results suggest that the narrow HOMO/LUMO separation of tricyclic nonclassical thiophenes can be carried over to their co-polymers by using them as building blocks for the co-polymers. [source]

    FTIR Spectroscopic and Theoretical Study of the Photochemistry of Matrix-isolated Coumarin

    Nihal Ku
    The infrared spectrum of monomeric unsubstituted coumarin (C9H6O2; 2H -1-benzopyran-2-one), isolated in solid argon at 10 K is presented and assigned. The UV-induced (, > 200 nm) unimolecular photochemistry of the matrix-isolated compound was studied experimentally. Three main photoreactions were observed: (a) decarboxylation of the compound and formation of benzocyclobutadiene and CO2, with the Dewar form of coumarin as intermediate; (b) isomerization of the compound, leading to production of a conjugated ketene; and (c) decarbonylation, leading to formation of CO and benzofuran complex. Further decomposition of benzofuran to produce ethynol is suggested. Photochannels (a) and (b) correspond to those previously observed for matrix-isolated ,- pyrone and its sulfur analogs (Phys. Chem. Chem. Phys. 2004, 6, 929; J. Phys. Chem. A 2006, 110, 6415), while route (c) is similar to the UV-induced photochemistry of coumarin in the gaseous phase (J. Phys. Chem. A 2000, 104, 1095). Interpretation of the experimental data is supported by extensive calculations performed at the B3LYP/6-311++G(d,p), MP2/6-31G(d,p) and MP2/6-311++G(d,p) levels. [source]

    Theoretical Study on Thermodynamic and Detonation Properties of Polynitrocubanes

    Xue-Hai Ju
    Abstract We investigated the heat of formation (,fH) of polynitrocubanes using density functional theory B3LYP and HF methods with 6-31G*, 6-311+G**, and cc-pVDZ basis sets. The results indicate that ,fH firstly decreases (nitro number m=0,2) and then increases (m=4,8) with each additional nitro group being introduced to the cubane skeleton. ,fH of octanitrocubane is predicted to be 808.08,kJ mol,1 at the B3LYP/6-311+G** level. The Gibbs free energy of formation (,fG) increases by about 40,60,kJ mol,1 with each nitro group being added to the cubane when the substituent number is fewer than 4, then ,fG increases by about 100,110,kJ mol,1 with each additional group being attached to the cubic skeleton. Both the detonation velocity and the pressure for polynitrocubanes increase as the number of substituents increases. Detonation velocity and pressure of octanitrocubane are substantially larger than the famous widely used explosive cyclotetramethylenetetranitramine (HMX). [source]

    Photocatalytic Activity and Electronic Structure Analysis of N-doped Anatase TiO2: A Combined Experimental and Theoretical Study

    H. Gao
    Abstract N-Doped TiO2 photocatalysts were prepared by a hydrothermal method with tetra- n -butyl titanate (TTNB) and triethanolamine as precursors. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-visible diffuse reflectance spectra (DRS), respectively. Photocatalytic activities of the anatase products were investigated on the degradation of methyl orange (MO). The incorporation of nitrogen impurity in anatase TiO2 was studied by the first-principles calculations based on the density functional theory (DFT). The calculated electronic band structures for substitutional and interstitial N-doped TiO2 indicated the formation of localized states in the band gap, which lied above the valence band. Excitation from the impurity states of N 2p to the conduction band could account for the optical absorption edge shift toward the lower energies. It was consistent with the experimentally observed absorption of N-doped samples in the visible region. [source]

    ChemInform Abstract: Soluble Semiconductors AAsSe2 (A: Li, Na) with a Direct-Band-Gap and Strong Second Harmonic Generation: A Combined Experimental and Theoretical Study.

    CHEMINFORM, Issue 24 2010
    Tarun K. Bera
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    ChemInform Abstract: Theoretical Study of Mg+,X and [X,Mg,Y]+ Complexes Important in the Chemistry of Ionospheric Magnesium (X, Y: H2O, CO2, N2, O2, and O).

    CHEMINFORM, Issue 43 2009
    Richard J. Plowright
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    ChemInform Abstract: Growth Mechanism and Chemical Bonding in Scandium-Doped Copper Clusters: Experimental and Theoretical Study in Concert.

    CHEMINFORM, Issue 28 2009
    Tibor Hoeltzl
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    ChemInform Abstract: An ab initio Theoretical Study of the Electronic Structure of UO2+ and [UO2(CO3)3]5- .

    CHEMINFORM, Issue 19 2009
    Fernando Ruiperez
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    ChemInform Abstract: A Gaussian-3 Theoretical Study of Small Silicon,Lithium Clusters: Electronic Structures and Electron Affinities of SinLi - (n = 2,8).

    CHEMINFORM, Issue 3 2009
    Dongsheng Hao
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]