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1.
Emildo Marcano Emilio Squitieri Juan Murgich Humberto Soscún 《Journal of Molecular Structure》2009,911(1-3):81-87
Hatree–Fock calculations at ab initio and semiempirical levels were carried out for the averaged polarizability α and second hyperpolarizability γ of two pairs of quadrupolar isomers with different donor and acceptor groups. These properties were correlated with the antibonding/bonding π occupation number (π*/π ratio). It was found that isomers with extended π systems had low π*/π ratios and high α and γ values, while low α and γ values were obtained for isomers with large π*/π ratios and no extended π system. The PM3 and PM6 α values were found to be in excellent agreement with the HF/6-31+G(d,p) ones. The PM3 values for γ were significantly larger than those calculated by HF/6-31+G(d,p), with an average PM3/HF ratio of 1.43. The PM6 results were noticeably better with a ratio of 0.85. The calculation of α and γ at MP2/6-31+G(d,p) level for representative isomers showed that the contribution of the electron correlation to their values was small and that the HF/6-31+G(d,p) method provides reliable values at much lower computational cost. 相似文献
2.
F. Loncke H. Vrielinck P. Matthys F. Callens J.P. Tahon P. Leblans 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,69(5):1322
The electron paramagnetic resonance (EPR) spectrum of needle image plates of CsBr doped with Eu2+, which are proposed as new X-ray storage phosphors for computed radiography, is studied at room temperature and Q-band microwave frequencies (34 GHz). X-ray diffraction analysis demonstrates that the CsBr:Eu2+ needles have an 0 0 1 out of plane (perpendicular to the plate) orientation, and contrary to expectation that the in plane orientation is not random. The room temperature EPR spectrum is attributed to a single centre which is related to Eu2+ with axial 0 0 1 symmetry. Using the spin Hamiltonian parameters extracted from the spectrum recorded with the magnetic field parallel to the needles’ axes, we convincingly simulate both the spectrum of a powdered image plate and the single crystal like angular dependence of intact pieces of image plate. The knowledge of the symmetry of this centre, which appears to be related with the radiation sensitivity of the plate, presents a first step in finding its model and role in the X-ray storage process. 相似文献
3.
Business presentations of the IMRP-2006—the 14th International Meeting of Radiation Processing held in Kuala Lumpur, Malaysia—are reviewed. They represent significant technical developments that are of interest to the radiation processing community. The full presentations can be accessed at the website of the International Irradiation Association at http://www.doubleia.org/. 相似文献
4.
Yong-Qing Qiu Xiao-Dong Liu Shi-Ling Sun Min Fan Zhong-Min Su Rong-Shun Wang 《Journal of Molecular Structure》2008,863(1-3):66-72
Density functional theory (DFT) B3LYP method was employed to calculate electron properties and the second-order nonlinear optical (NLO) responses of the derivatives which were formed by (C5H5)Co(C2B4H6) and CHCHC6H4NO2, CHCHC6H4NH2. The results show: when H atom of (C5H5)Co(C2B4H6) is substituted by CHCHC6H4NO2, the βtot values of isomers are all slightly smaller than that of ferrocene (Fc) derivative (FcCHCHC6H4NO2). However, when H atom of (C5H5)Co(C2B4H6) is substituted by CHCHC6H4NH2, the βtot values of isomers are close to that of ferrocene (Fc) derivative (FcCHCHC6H4NH2). It indicates that (C5H5)Co(C2B4H6) can be either a donator or an acceptor. 相似文献
5.
Mirosaw Jaboski 《Journal of Molecular Structure》2007,820(1-3):118-127
A group of model systems which may form chelate-type structures with intramolecular CH Y (Y = O, S) contact is investigated computationally. The existence of several conformers permits to identify a reference molecule without the CH Y intramolecular contact and to establish the blue-shifting character of this interaction. The CH stretching frequency in chelate forms is found to increase with respect to its value in the reference system. A parallel decrease of the CH bond distance is also established. The blue-shifting character of the intramolecular CH Y contact is interpreted in terms of the sterically enforced repulsion between the hydrogen atom in CH and the electron donor Y. This interpretation is supported by the negative (repulsive) estimates of the energy contribution due to CH Y contacts. 相似文献
6.
Stephanie M. Villano Nicole Eyet W. Carl Lineberger Veronica M. Bierbaum 《International journal of mass spectrometry》2009,280(1-3):12
The reactivities of mono- and dihalocarbene anions (CHCl−, CHBr−, CF2−, CCl2−, and CBrCl−) were studied using a tandem flowing afterglow-selected ion flow tube instrument. Reaction rate constants and product branching ratios are reported for the reactions of these carbene anions with six neutral reagents (CS2, COS, CO2, O2, CO, and N2O). These anions were found to demonstrate diverse chemistry as illustrated by formation of multiple product ions and by the observed reaction trends. The reactions of CHCl− and CHBr− occur with similar efficiencies and reactivity patterns. Substitution of a Cl atom for an H atom to form CCl2− and CBrCl− decreases the rate constants; these two anions react with similar efficiencies and reactivity trends. The CF2− anion displays remarkably different reactivity; these differences are discussed in terms of its lower electron binding energy and the effect of the electronegative fluorine substituents. The results presented here are compared to the reactivity of the CH2− anion, which has previously been reported. 相似文献
7.
Hiroshi Morita Anzu Kasai Jan ubrt Zdenk Bastl 《Journal of photochemistry and photobiology. A, Chemistry》2009,206(2-3):205-212
Under UV light irradiation on a gaseous mixture of Fe(CO)5 and Co(CO)3NO, both the crystalline deposits with sizes of 5 and 18 μm and the spherical particles with a mean diameter of 0.3 μm were produced. From FT-IR spectra and SEM–EDS analysis, it was suggested that the chemical structure of the crystalline deposits was the one of Fe2(CO)9 being modified by involving Fe(CO)Co bond. By decreasing a partial pressure of Fe(CO)5 to 0.5 Torr in the gaseous mixture, only the spherical aerosol particles could be produced. Chemical composition of the particles was rich in Co species. From the disappearance of bridging CO band in the FT-IR spectra of the particles and the appearance of CO bands coordinated to a metal atom, Fe atom in Fe(CO)4 was suggested to be coordinated by the O atom in bridging CO bond in Co(CO)Co structure and/or in α-diketone structure which was formed from two CO groups in dicobalt species. Chemical compositions of the crystalline deposits and the spherical particles were influenced differently by the application of a magnetic field. Atomic ratio of Fe to Co atom decreased in the crystalline deposits whereas it increased in the spherical particles with increasing magnetic field up to 5 T. Linearly aggregated particles (i.e., particle wires) as long as 30 μm were produced on the front side of a glass plate placed at the bottom of the irradiation cell. 相似文献
8.
Charles W. Bock Joseph D. Larkin Stephen S. Hirsch J.B. Wright 《Journal of Molecular Structure》2009,915(1-3):11-19
Computed reaction enthalpies, free energies, and activation barriers in vacuo are presented for the nucleophilic detoxification of the organophosphorus compounds (H)(HO)P(O)F, (H)(H3CO)P(O)F and (H3C)(CH(CH3)2O)P(O)F via the reaction R1OH + (R2)(R3O)P(O)F → (R2)(R3O)P(O)(OR1) + HF for a wide variety of R1OH nucleophiles. Density functional theory at the B3LYP/6-311++G(d,p) computational level was employed for all the calculations. A multi-step Wright-type reaction mechanism [J. B. Wright, W.E. White, J. Mol. Struct. (THEOCHEM) 454 (1998) 259], which proceeds via a proton transfer from the nucleophile to the fluorine atom through the phosphinyl oxygen atom, was consistently found to have a lower activation barrier in the gas-phase than for the corresponding mechanism that operates via a proton transfer from the nucleophile directly to the fluorine atom. Of the nucleophilic agents investigated, peroxybenzoic acid and o-iodosobenzoic acid had the lowest classical activation barrier for the Wright-type mechanism. 相似文献
9.
Tao Hong Li Chuan Ming Wang Shi Wen Yu Xiang Yi Liu Hui Fu Xiao Guang Xie 《Journal of Molecular Structure》2009,915(1-3):105-111
The reaction of ground-state Y with 2-butyne has been investigated in detail using B3LYP method. Four pathways for elimination of H2 were identified. Two isomers, Y(HCCC)CH3 and Y(H2CCCCH2) were assigned to the observed product, YC4H4. The calculated PESs suggest that the concerted H2-elimination leading to Y(H2CCCCH2) + H2 product is the most favorable pathway. For the elimination of CH3, combining the results of this work with our previous study on Y + propyne reaction, a general mechanism for the reactions of Y with 2-alkynes bearing RCCCH3 structure was established: Y + RCCCH3 → π-complex → TS(H-migration) → HY(CH2CC)R → TS (CC insertion) → (CH2)HYCCR → TS(H-migration) → H3CYCCR → CH3 + YC2R. Such mechanism was found to be always energetically more favorable than the direct sp–sp3 CC bond insertion mechanism. Further, such mechanism can also be applied to the elimination of CH4 and it can be described as: Y + CH3CCCH3 → π-complex → TS (H-migration) → HY(H2CCC)CH3 → TS(CC insertion) → (H2CCC)HYCH3 → TS(H-migration) → CH4 + YC3H2. 相似文献
10.
Harumi Sato Rumi Murakami Katsuhito Mori Yuriko Ando Isao Takahashi Isao Noda Yukihiro Ozaki 《Vibrational Spectroscopy》2009,51(1):132-135
Infrared reflection–absorption (IR-RAS) and transmission spectra were measured for poly(3-hydroxybutyrate) (PHB) thin films to explore its specific crystal structure in the surface region. As IR-RAS is sensitive to the vibration mode of perpendicular orientation of the surface, differences between IR-RAS and transmission spectra indicate an orientation of the lamella structure in the surface of PHB thin films. The relative intensity of the crystalline CO stretching band in the IR-RAS spectrum is significantly weaker than that in the transmission spectrum. It may be concluded that the transient dipole moment of the CO stretching mode of the crystalline state is not oriented perpendicular but nearly parallel to the substrate surface. On the other hand, the relative intensity of the band at 3009 cm−1 due to the C–H stretching mode of the C–HOC hydrogen bonding is similar between the IR-RAS and transmission spectra, suggesting that the C–H bond is oriented neither perpendicular nor parallel to the substrate surface but in an intermediate direction. Since the CO group of the C–HOC hydrogen bonding is oriented nearly parallel to the surface and its C–H group is in the intermediate direction, it is very likely that the C–HOC hydrogen bonding has a somewhat bent structure. These results are in good agreement with our previous conclusion that the C–HOC hydrogen bonding of PHB exists along the a-axis (not the b-axis) between the CH3 group of one helix and the CO group of another helix. 相似文献
11.
Mechanisms for pyrolysis of poly(α-methylstyrene) must rationalize high selectivity for monomer formation, negligible formation of volatile oligomers, and notably slow decrease in molecular weight compared with the rate of weight loss, i.e., unzipping dominates both back-biting and transfer. Backbone homolysis should form both a tert-benzylic radical Rtb and a prim radical Rp, with formation of the latter potentially supplemented in chain propagation steps emanating from the former. Hence product-forming pathways characteristic of each are expected to compete. Simulations of initial product distributions based on assigned rate constants for chain propagation steps indicate that Rtb is indeed predicted to efficiently unzip with minimal transfer or back-biting. However, Rp is predicted to give comparable amounts of transfer and back-biting with minimal unzipping, behavior inconsistent with experimental data. The proposed escape from this impasse is a previously unrecognized pathway, 1,2-phenyl shift in Rp to form a tert radical. If it undergoes β-scission, the net result is an inter-conversion of Rp to Rtb. Quantitative simulations suggest that this sequence is indeed highly competitive with other reactions of Rp and thus efficiently subverts the otherwise expected propagation of chains emanating from Rp. 相似文献
12.
S.C. Nunes V. de Zea Bermudez M.M. Silva M.J. Smith E. Morales R.A. S Ferreira L.D. Carlos J. Rocha 《Solid State Sciences》2006,8(12):1484-1491
Zinc triflate (Zn(CF3SO3)2)-doped sol–gel derived di-urea cross-linked POE/siloxane ormolytes (designated as di-ureasils) with ∞>n1 (where the salt content is expressed as n, the molar ratio of oxyethylene moieties to Zn2+ ions) were investigated. The hybrids with n5 are entirely amorphous; those with n>10 are thermally stable up to approximately 305 °C. The siliceous network of representative samples (n=200 and 10) is essentially composed of (SiO)3Si(CH2)-environments and is thus highly branched. The distance between the structural units in samples with 200n10 and n7 is 4.2 and 4.3 Å, respectively. The estimated interdomain distance is 11 and 13 Å for xerogels with 200n20 and n10, respectively. At n=1 a crystalline POE/Zn(CF3SO3)2 complex of unknown stoichiometry is formed. The conductivity maxima are located at n=60 () and n=20 () at 30 and 100 °C, respectively. 相似文献
13.
Robert Flammang Nomie Dechamps Pascal Gerbaux Pham-Cam Nam Minh Tho Nguyen 《International journal of mass spectrometry》2008,275(1-3):110-116
The MS/MS spectrum of the metastable molecular ions of dimethyl isophthalate 1 differs from that of the isomeric dimethyl terephthalate 2 by the observation of, inter alia, a quite intense loss of C,H2,O ascribed to formaldehyde. Results obtained using a combination of mass spectrometry techniques suggest that this process could consist of an isomerization reaction of the molecular ion into an ion–neutral complex (INC) linking a benzoyl radical and neutral formaldehyde to a proton [ArCOHOCH2]+. Within the complex, a proton transfer catalyzed by formaldehyde occurs resulting in the production of an ionized cyclohexadienylidene methanone (ketene) structure. 相似文献
14.
Duane Choquesillo-Lazarte María del Pilar Brandi-Blanco Isabel García-Santos Josefa María Gonzlez-Prez Alfonso Castieiras Juan Nicls-Gutirrez 《Coordination chemistry reviews》2008,252(10-11):1241
The available crystal structure information in the CSD database on ternary species prepared by the reaction of diverse copper(II) complexes (CuL) and purine, adenine and guanine or related purine derivatives is considered in order to deepen the intra-molecular interligand interactions affecting the molecular recognition patterns of the ‘metal complex + purine nucleobase’ and closely related systems. The degree of protonation and the possibilities of different tautomeric forms in the purine-like moieties are taken into account. The main conclusion is a general trend to form a CuN(purine-like) coordination bond which can be reinforced by an intra-molecular interligand H-bonding interaction. NH(purines)A (O or Cl acceptor) or NH(amino ligand L)O6(oxo-purines) are commonly observed. In addition, selected examples revealed that the presence of a variety of non-coordinating groups in L or in the purine-like nucleobases can significantly influence the structurally observed molecular recognition pattern. Moreover, examples are known where binuclear cores of the types CuII2(μ2-N3,N9-adeninate)4(aqua)2 or CuI2(μ2-N3,N9-adeninate)2(aqua)2 recognise CuL chelates by means of the expectable pattern (CuN7 coordination bond + N6HO(L) interaction). 相似文献
15.
Hydrogen-bond structures in poly(2-hydroxyethyl methacrylate) (PHEMA) were investigated by infrared (IR) spectroscopy and quantum chemical calculations (QCC). A monomer of 2-hydroxyethyl methacrylate (HEMA) and model compounds of methyl acetate (MA) and methanol (MeOH) were also used. Evidences for OHOC and OHOH types of hydrogen-bonds were observed in an IR spectrum of a PHEMA solid. It was estimated from the present study that 47.3% of OH groups on the PHEMA side chain terminal are engaged in the OHOC type of hydrogen-bond, while the rest contributes to the OHOH type of hydrogen-bond. 相似文献
16.
Tabulating the structures and characteristic NMR properties of 17 iron complexes, 98 ruthenium complexes and 70 osmium complexes that contain dihydrogen or compressed dihydride ligands reveals a variety of trends. The HH bond lengths increase from similar Fe(II) to Ru(II) to Os(II) complexes. Iron(II) displays a narrow range of HH distances for stable complexes. Electronegative atoms Cl and O, when attached on the metal trans to the dihydrogen ligand, result in elongation of the HH bond relative to more electropositive atoms H, C, P and N. The family of cyclopentadienyl ligands also causes this elongating effect. The dihydrogen ligands with short HH distances and weak interactions with the metal, especially on iron and ruthenium are in the fast spinning regime. One exception is the biporphyrin complex of ruthenium with the side-on bridging H2 ligand which has an HH distance of 118 pm but is in the fast spinning regime. There are some ruthenium complexes with HH distances greater than 110 pm that are in the slow motion regime and several complexes of osmium with HH distances greater than 130 pm that are in this regime. The large JHH due to quantum mechanical exchange coupling are observable for some of these osmium complexes with HH distances in the range of 140–160 pm. The dihydrogen ligands in many complexes appear to have librational motions or other motions that place them in the intermediate motion regime. New equations to correlate JHD with HH distances for ruthenium dihydrogen complexes and for osmium dihydrogen complexes are introduced here. 相似文献
17.
Toms Pea Ruiz Manuel Fernndez Gmez Juan Jesús Lpez Gonzlez Anna E. Koziol 《Chemical physics》2006,320(2-3):164-180
Intermolecular forces of C–HO, C–Hπ, COCl and ππ types are present in the stable triclinic crystal structure of 5-chloro-1-indanone. They are analysed from a geometrical point of view supported in some extent by the analysis of the vibrational spectrum of the titled compound. Moreover, the molecular structure of the isolated species is calculated by using ab initio as well as density functional theory (DFT) methods together an assortment of basis sets. In order to obtain some information about the influence of intermolecular forces on the molecular structure, the calculated geometries of a free molecule were compared with the experimental solid phase geometry determined by X-ray crystallography.An analysis and assignment of the vibrational spectrum of the 5-chloro-1-indanone is accomplished by using IR and Raman experimental data along with Pulay et al.’s scaled quantum mechanical force field (SQM) methodology starting from the theoretical B3LYP/6-31G(d) and BLYP/6-31G(d) force fields under Cs symmetry. 相似文献
18.
Michael Verschoor-Kirss Joszef Kreisz William Feighery William M. Reiff Christoph M. Frommen Rein U. Kirss 《Journal of organometallic chemistry》2009,694(20):3262-3269
Copper catalyzed [3+2] cycloaddition reactions between ethynylferrocene and benzylazides yields 1-benzyl-4-ferrocenyl-1,2,3-triazoles (2–5). Reaction between phenylacetylene and azidoferrocene yields 1-ferrocenyl-4-phenyl-1,2,3-triazole (6). Anodic electrochemistry of 2–6 suggests reversible oxidation at potentials more positive than ferrocene. Chemical oxidation of 2 and 3-ferrocenylpyrrole (1) with dichlorodicyanoquinone (DDQ) yields the salts [2+] [DDQ−] and [1+] [DDQ−], respectively. 57Fe Mössbauer spectroscopy reveals the presence of low-spin FeII in [1+][DDQ−] while FeII is oxidized to low-spin FeIII in [2+][DDQ−]. Magnetization measurements indicate that [1+][DDQ−] is paramagnetic and cannot be viewed as a simple neutral charge transfer complex reminiscent of the mixed stack diamagnetic [ferrocene]0[TCNE]0. 相似文献
19.
E. Germn I. Lpez-Corral A. Juan G. Brizuela 《Journal of molecular catalysis. A, Chemical》2008,290(1-2):23-29
The adsorption of cyclopentene (c-C5H8) on Ni(1 1 1) was studied using DFT and semiempirical calculations. Preferred site and geometry calculations were carried out considering a Ni(1 1 1) surface and a unit cell of 64-atoms. The tetrahedral threefold hollow position was identified as the most favorable site, with a surface-molecule minimum distance of 1.83 Å. A bending structure is adopted when the molecule is adsorbed where the carbon atoms of the double bond are closer to the surface forming an angle of 160° among non-equivalents carbon atoms. The metal surface was represented by a two-dimensional slab with an overlayer of c-C5H8/Ni of 1/9 ratio. We also computed the density of states (DOS) and the crystal orbital overlap populations (COOP) corresponding to CC, CNi, CH, and NiNi bonds. We found that both NiNi bonds interacting with the ring, and the CC bond are weakened after adsorption, this last bond is linked significantly to the surface. The hydrogen atoms belonging to the saturated carbon atoms also participate in the adsorbate–surface bonding. The main interactions include the 4s, 3pz and 5dz2 bands of nickel and 2pz bands of the carbon atoms of the double bond. 相似文献
20.
Effects of some factors during electrochemical degradation of phenol by hydroxyl radicals 总被引:1,自引:0,他引:1
Hydroxylation of aromatic compounds has been used extensively as a measure of hydroxyl radicals (OH) formation. In this paper, salicylic acid (2-HBA) was used to trap OH in the process of electrolysis with a couple of Ti-base lead dioxide electrodes in different conditions. Aqueous solution of 2-HBA, a couple of Ti-base lead dioxide electrodes and an AC power were used in the course of OH formation, and then the solution containing 2-HBA and 2,5-dihydroxybenzoic acid (2,5-DHBA) was analyzed by High Performance Liquid Chromatography (HPLC) with fluorescence detector. This method can help us to better understand the reaction mechanism of OH from the viewpoint of quantity.In the same conditions of electrolysis, Total Organic Carbon (TOC) of phenol solutions were detected to identify the effects of some factors during this electrochemical process, because the strong oxidation ability of OH can mineralize the organic pollutants totally and finally achieve the goal of water treatment. The results show that high pH value of electrolyte and high frequency of the AC power are favorable for the generation of OH, however, CO32− is opposite to them. 相似文献