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1.
Vibrational energy transfer has been studied in S18O2, following pumping of the symmetric stretch (ν1) by a Q-switched CO2 laser. Fluorescence from the asymmetric stretch (ν3) is monitored as a function of time following the laser pulse. This fluorescence rises with a rate constant of 74 ± 10 ms?1 torr?1, and then decays with a rate constant of 3.6 ± 0.1 ms?1 torr?1 for the S18O2 itself. The effect of rare gases on the rise and fall rates was also studied. The results agree well with those on S16O2 and are consistent with a double V-V picture in which the excitation is distributed rapidly between the stretches, but is shared with the bend much more slowly. This produces molecules in which the stretches are much “hotter” than the bend, giving rise to possibilities of laser action on the stretch-to-bend transitions and mode-selective vibrational enhancement of chemical reactions. Also, new results have been derived on the kinetics of V-V processes in mixtures. V-V transfer in various isotopic mixtures of SO2 has been studied and the kinetic analysis indicates that S18O2 and S16O2 exhibit the same V-V rates. 相似文献
2.
Donald J. Darensbourg 《Journal of organometallic chemistry》1979,174(3):C70-C76
The oxygen-18 isotope shifts on the natural abundance 13C spectra of oxygen-18 enriched samples of W(CO)8 and W(CO)5PPh3 have been observed to be 0.040 ppm (0.61 Hz at 15.03 MHz) upfield from that of a 13C nucleus bearing an oxygen-16 atom. 相似文献
3.
Babak Behnam Azad Rezwan Ashique Gary J. Schrobilgen 《Journal of fluorine chemistry》2008,129(1):22-27
Fluorine-18 labeled aromatic amino acids are routinely used as tracers in positron emission tomography (PET) to study in vivo metabolic processes. The most versatile method for the production of such radiotracers is electrophilic fluorination of the aromatic amino acid with [18F]F2, which is most commonly produced by the gas-phase nuclear reaction 18O(p, n)18F. Although [18F]F2 is the major product, considerable amounts of [18F]OF2 (up to 20%) are also produced. Electrophilic fluorination reactions of l-phenylalanine, 3-nitro-l-tyrosine, 4-nitro-dl-phenylalanine, 3,4-dihydroxyphenyl-l-alanine (l-DOPA), 3-O-methyl-l-DOPA, 3,4-dimethoxy-l-phenylalanine, p-tyrosine and o-tyrosine in H2O and of m-tyrosine in anhydrous HF (aHF), CF3SO3H, CF3COOH, CH3COOH, HCOOH and H2O using OF2 were investigated. Although F2 is an efficient fluorinating agent in aHF, electrophilic fluorination reactions using OF2 were shown to be most efficient in less acidic media such as H2O. In addition, and contrary to reports that OF2 and F2 have similar reactivities, m-tyrosine was the only aromatic system studied that was fluorinated by OF2 and this was optimum in H2O for the fluorinated m-tyrosine isomers (total yield, 4.35 ± 0.04%). The presence of [18F]OF2 byproduct has no significant impact on the fluorination of aromatic amino acids investigated in this study and the subsequent production of their corresponding 18F-labeled radiotracers for patient use. 相似文献
4.
Friedrich Hammerschmidt 《Monatshefte für Chemie / Chemical Monthly》1991,122(5):389-398
Summary Racemic methyl O-benzyllactate was reduced to the alcohol, transformed into the bromide and reacted with triethylphosphite to give the diethylphosphonate. Removal of protecting groups afforded a phosphonic acid which was purified as its cyclohexylammonium salt. (S)-Ethyl and (R)-isobutyl O-benzyllactate were reduced with LiAlD4 to the corresponding dideuteriated alcohols, which were transformed in the same way as the racemic compound into the chiral (2-hydroxy-[1,1-2H2]propyl)phosphonic acids. The optical purity of alcohols (S)- and (R)-6 b was determined by derivatisation with (+)-MTPA-Cl and1H-NMR-spectroscopy to be 98%. Exchange of the carbonyl-16-oxygen atom of 2-oxopropylphosphonate for oxygen-18 from H2
18O, reduction with NaBH4, deprotection and addition of cyclohexylamine yielded the salt (±)-18 of (2-[18O]hydroxypropyl)phosphonic acid. 相似文献
5.
Resonance Raman scattering has been observed from metastable O2 molecules produced in single crystals of NaClO3 by γ-irradiation at 300 K. Evidence that the observed bands are due to O2 is provided by the Raman spectrum of irradiated 18O enriched NaClO3 in which bands due to 16O2, 16O 18O, and 18O2 were identified. The Raman band at 1544 cm?1 ascribed to metastable O2 disappears on bleaching with intense 4880 Å radiation enabling the identification of a weaker band at 1557 cm?1 that is assigned to the stable form of O2. 相似文献
6.
The interactions of the sulfonium ions (CH3)3S+, (CH3)2S+CH2CO2
–, and (CH3)2S+-CH2CH2CO2
– with up to four water molecules have been studied by ab initio molecular orbital methods. Complexes of (CH3)3S+ with one to three water molecules involve strong electrostatic sulfur-oxygen interactions; in contrast, the sulfide (CH3)2S interacts with water molecules via weak S-H hydrogen bonds, suggesting that methyl-group transfer from (CH3)3S+ in aqueous solution involves a significant alteration of the hydration pattern around the sulfur atom. Two conformers of (CH3)2S+CH2CO2
– were found that display sulfur-oxygen distances which are approximately 0.3 å less than the sum of the sulfur and oxygen van der Waals radii, indicating a strong intramolecular electrostatic interaction. For the complexes (CH3)2S+CH2CO2
–·nH2O(n =1–4), water interacts primarily with the carboxylate group via hydrogen bonds, rather than electrostatically with the sulfur atom, although in complexes with the three- and four-water complexes, the proximity of the positively charged sulfur atom to the carboxylate group significantly alters the hydration pattern compared to that in the corresponding of complexes CH3SCH2CO2
–· Thus, methyl transfer from (CH3)2S+CH2CO2
– to an acceptor in aqueous solution also involves substantial changes in the hydration pattern around the carboxylate group. 相似文献
7.
Two new thioantimonates [M(dap)3]Sb4S7 (M = Ni2+ ( 1 ) and Co2+ ( 2 )) were synthesized under solvothermal conditions by the reaction of NiS (or Co metal), Sb and S in an aqueous solution of 1,2‐diaminopropane (dap). Compounds 1 and 2 are isostructural. The polymeric [Sb4S72?]n anion is composed of two SbS3 trigonal pyramids and two SbS4 units. The SbS3 and SbS4 units are interconnected by corners and edges to build a 2‐D puckered layer with Sb4S4 and Sb16S16 heterorings. The apertures of the large Sb16S16 hetero‐rings are filled by two [M(dap)3]2+ complex cations which serve as template ions. The band gaps of 2.44 eV for 1 and 2.43 eV for 2 have been estimated from optical absorption spectra. 相似文献
8.
Dy3OF5S: The First Oxyfluoride Sulfide of the Lanthanides While trying to synthesize DyFS with the PbFCl‐type crystal structure by the reaction of DyF3 with dysprosium and sulfur in 1:2:3‐molar ratios at 850 °C in gas‐tight sealed tantalum ampoules, oxygen contaminated educts (e.g. DyOF‐containing DyF3) were also applied occasionally. Consequently a small quantity of almost colourless, rod‐shaped single crystals of Dy3OF5S, the first oxyfluoride sulfide of the lanthanides, were formed in small quantities on adding equimolar amounts of NaCl as flux. Almost phase‐pure samples are obtained under otherwise analogous reaction conditions according to 2 Dy + 5 DyF3 + Dy2O3 + 3 S = 3 Dy3OF5S by deliberate addition of Dy2O3. In the hexagonal crystal structure (space group: P63/m; a = 942.58(8), c = 368.12(4) pm; c/a = 0.391, Vm = 85.285 cm3/mol, Z = 2) Dy3+ resides in nine‐fold anionic coordination (tricapped trigonal prism comprising 1.333 O2—, 5.667 F— and 2 S2—). The fractional numerical values for the “light anions” are due to two six‐fold point positions with the exclusive existence of F— in trigonal non‐planar coordination (CN = 3, d(F1—Dy) = 232 (1×) and 241 pm, 2×) on the one hand, but F— and O2— simultaneously in the ratio 2 : 1 in tetrahedral coordination of Dy3+ (CN = 4, d(F2/O—Dy) = 234 (2×), 236 and 241 pm, 1× each) on the other. Finally, a trigonal prismatic Dy3+ coordination (d(S—Dy) = 290 pm, 6×) is attributed to the S2— anions. From the data of the single crystal X‐ray structure analysis, no indication of an ordering of O2— and F— is obtained, its true nature as an oxyfluoride sulfide, however, is unambiguously confirmed by electron‐beam microanalysis on Dy3OF5S. 相似文献
9.
Aaron Chin Yit Tay Benjamin J. Frogley David C. Ware Jeanet Conradie Abhik Ghosh Penelope J. Brothers 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(10):3089-3093
The first examples of diboron complexes of the tetrapyrroles octaethylporphyrazine (OEPz) and 2,9,16,23‐tetra‐t‐butyl‐phthalocyanine (Pc) are reported, counterpoints to the better known monoboron tripyrroles, subporphyrazine and subphthalocyanine. Two stereochemical possibilities are observed, with cisoid‐B2OF2(OEPz), both cisoid‐B2OPh2(OEPz) and transoid‐B2OPh2(OEPz), transoid‐B2OF2(Pc) and cisoid‐B2OPh2(Pc) having been isolated and characterised, including structure determinations for the OEPz complexes. This variation in stereochemistry, which can be extended to include the previously reported transoid‐B2OF2(porphyrin), cisoid‐[B2OF2(corrole)]?, and both transoid‐ and cisoid‐B2OF2(calixphyrin), prompted a wider DFT study to elucidate the factors influencing the stereochemical preferences. This shows that the cisoid/transoid preference is correlated to the ease with which the macrocycle accommodates a rectangularly distorted N4 cavity. 相似文献
10.
Kazuhiro Endo Hideo Ihara Kazuhiro Watanabe Shun-Ichi Gonda 《Journal of solid state chemistry》1982,44(2):268-272
X-Ray photoelectron spectra of TiS3 with a one-dimensional structure were measured. TiS3 may be regarded as Ti4+(S2)2?S2? with pairs of S atoms (S2) and isolated S atoms. The spectra of the sulfur core-levels are assigned by comparison with those of TiS2, where all S atoms are largely separated. The binding energy of the S2 pairs is found to be 1.4 eV higher than that of the isolated S atoms, which is consistent with the larger negative charge of the isolated atoms. The structures of the valence band of TiS3 are discussed in terms of a molecular orbital scheme for the S2 pairs. 相似文献
11.
Absolute vibrational quantum numbers for the SO+ (A2Π—χ2Πr) emission system have been determined by measurement of isotope shifts between S16O+ and S18O+ bands. It has been found that the tentative ν″ values reported previously should be decreased by one vibrational quantum number, The definite molecular constants for the SO+ (A2Π,χ2Πr) states are determined and compared with photoelectron spectroscopic data. 相似文献
12.
The ν1?2ν2 Fermi diad of OF2 at 928 cm?1 was investigated by IR-MW double resonance using CO2 and N2O lasers. Using the data of Morino (ref. 1) and the additional rotational transitions measured in this work, a partial distortion analysis of the states (1,0,0)′ and (0,2,0)′ could be carried out. The accurately determined frequencies of five IR transitions in the ν′1 band and of two in the ν′2 band allowed the band centres to be calculated in both cases. 相似文献
13.
An O4 intermediate is postulated instead of O4? for the homomolecular oxygen exchange reaction on ZnO (only at liquid nitrogen temperatures) by the parallel observations of O2? using oxygen-17 and of gas phase oxygen using oxygen-18. 相似文献
14.
Yilei Hu Dr. Chao Wu Dr. Xingxing Jiang Dr. Kaining Duanmu Prof. Zhipeng Huang Prof. Zheshuai Lin Prof. Mark G. Humphrey Prof. Chi Zhang 《Angewandte Chemie (International ed. in English)》2023,62(52):e202315133
The development of urgently-needed ultraviolet (UV)/deep-UV nonlinear optical (NLO) materials has been hindered by contradictory requirements of the microstructure, in particular the need for a strong second-harmonic generation (SHG) response as well as a short phase-matching (PM) wavelength. We herein employ a “de-covalency” band gap engineering strategy to adjust the optical linearity and nonlinearity. This has been achieved by assembling two types of transition-metal (TM) polyhedra ([TaO2F4] and [TaF7]), affording the first tantalum-based deep-UV-transparent NLO materials, A5Ta3OF18 (A = K (KTOF), Rb (RTOF)). Experimental and theoretical studies reveal that the highly ionic bonds and strong electropositivity of tantalum in the two oxyfluorides induce record short PM wavelengths (238 (KTOF) and 240 (RTOF) nm) for d0-TM-centered oxides, in addition to strong SHG responses (2.8 × KH2PO4 (KTOF) and 2.6 × KH2PO4 (RTOF)), and sufficient birefringences (0.092 (KTOF) and 0.085 (RTOF) at 546 nm). These results not only broaden the available strategies for achieving deep-UV NLO materials by exploiting the currently neglected d0-TMs, but also push the shortest PM wavelength into the short-wavelength UV region. 相似文献
15.
Normal vibrations of ethylbenzene in the first excited state have been studied using resonant two-photon ionization spectroscopy. The band origin of ethylbenzene of S1←S0 transition appeared at 37586 cm-1. A vibrational spectrum of 2000 cm-1 above the band origin in the first excited state has been obtained. Several chain torsions and normal vibrations are obtained in the spectrum. The energies of the first excited state are calculated by the time-dependent density function theory and configuration interaction singles (CIS) methods with various basis sets. The optimized structures and vibrational frequencies of the S0 and S1 states are calculated using Hartree-Fock and CIS methods with 6-311++G(2d,2p) basis set. The calculated geometric structures in the S0 and S1 states are gauche conformations that the symmetric plane of ethyl group is perpendicular to the ring plane. All the observed spectral bands have been successfully assigned with the help of our calculations. 相似文献
16.
An ion chromatography‐inductively coupled plasma mass spectrometric (IC‐ICP‐MS) method for the speciation of sulfur compounds, namely sulfite [SO32?], sulfate [SO42?] and thiosulfate [S2O32?], was described. Ionic sulfur compounds were well separated in about 3 min by ion chromatography with a Hamilton PRP‐X100 column as the stationary phase and 60 mmol L?1 NH4NO3 and 0.1% v/v formaldehyde (HCHO) solution (pH = 7) as the mobile phase. The analyses were carried out using dynamic reaction cell (DRC) ICP‐MS. The sulfur‐selective chromatogram was determined at m/z 48 as 32S16O+ by using its reaction with O2 in the reaction cell. The method avoided the effect of polyatomic isobaric interferences at m/z 32 caused by 16O16O+ and 14N18O+ on 32S+ by detecting 32S+ as the oxide ion 32S16O+ at m/z 48, which is less interfered. The detection limit of various species studied was in the range of 3.6–4.6 ng S mL?1. The accuracy of the method has been verified by comparing the sum of the concentrations of individual sulfur compounds obtained by the present procedure with the total concentration of sulfur in several natural water samples. The recovery was in the range of 97–102% for various compounds studied. 相似文献
17.
Thomas J. Houser 《国际化学动力学杂志》1978,10(7):773-781
The kinetics of the H2-OF2 reaction was studied in the temperature range of 160°–310°C at 1 atm total pressure in a magnesium stirred-flow reactor. Initial concentration ranges were 1/2–1/2 mol·% OF2, 3/16–5 mol·% H2, and 1/4–5.0 mol·% O2; helium was used as the diluent. When the reactants were in a mole ratio of 3/2 (H2/OF2), the rate of disappearance of H2 was 1.5 times that of OF2, consistent with the previously reported stoichiometry. The rate of disappearance of OF2 was strongly influenced by OF2 concentration, weakly influenced by H2 concentration, and inhibited by the oxygen formed in the reaction. An increase in the surface area did not produce a significant change in the rate of reaction. These concentration dependencies led to a proposed ten-step mechanism from which was derived the following rate equation: where k0 is a complex combination of elementary rate constants and α and β are elementary rate constants. An Arrhenius treatment of k0 gave These experimental Arrhenius parameters are lower than those predicted from reported and estimated elementary rate constants. The possibility of heterogeneous contributions is discussed. 相似文献
18.
Asadollah Boshra Siamak Jadidi Maryam Goudarzi Samaneh Niroumand Maryam Mohammadi 《Journal of Cluster Science》2012,23(2):297-310
Endohedral derivatives of B16N16 nanocage (M@B16N16, M?=?Li+, Na+, K+, Mg2+, Ne, O2?, S2?, F?, Cl?) and its iso-electronic fullerne M@C32 have been employed to investigate the relation between the trapped atom/ion and electrophilicity of the B16N16 and C32 nanocages. The electrophilicity index, ??, of these endohedral nanocages has been evaluated from the ionization potential and the electron affinity computed by vertical ionization/affinity at the B3LYP/6-311++G(df,pd) level. Obtained results illustrate that the nature of trapped atom/ion affects HOMO-LUMO band gap, global electrophilicity indices and reactivity of B16N16 and C32 nanocages. Encapsulation B16N16 with different atom/ions may be a possible method for modifying HOMO-LUMO energy gap, electrophilicity and so chemical characteristics of and C32 nanocages. 相似文献
19.
Irvine J. Solomon 《Journal of fluorine chemistry》1980,16(6):588
The preparation and chemical and physical properties of the oxygen fluorides (OF2, OF, O2F2, OOF and O4F2) are reviewed. There has been speculation about the existence of other oxygen fluorides (O3F2, O3F, OSF2 and O6F2) but these have not been well-characterized. The first member, OF2, is much more stable than the other oxygen fluorides, and is also less-reactive. In addition to acting as a fluorinating agent and oxidizer, OF2 has been shown to be a source of the OF radical. Dioxygen difluoride is a powerful fluorinating agent, but if reacted under carefully controlled conditions, can be a source of the OOF radical. 相似文献
20.
Takatsugu Kanatani 《Journal of fluorine chemistry》2011,132(10):673-678
Electrochemical behavior of hexafluoroniobate (Nb(V)F6−), heptafluorotungstate (W(VI)F7−), and oxotetrafluorovanadate (V(V)OF4−) anions has been investigated in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPyrTFSA) ionic liquid at 298 K by means of cyclic voltammetry and chronoamperometry. Cyclic voltammograms at a Pt electrode showed that Nb(V)F6− anion is reduced to Nb(IV)F62− by a one-electron reversible reaction. Electrochemical reductions of W(VI)F7− and V(V)OF4− anions at a Pt electrode are quasi-reversible and irreversible reactions, respectively, according to cyclic voltammetry. The diffusion coefficients of Nb(V)F6−, W(VI)F7− and V(V)OF4− determined by chronoamperometry are 1.34 × 10−7, 7.45 × 10−8 and 2.49 × 10−7 cm2 s−1, respectively. The Stokes radii of Nb(V)F6−, W(VI)F7−, and V(V)OF4− in BMPyrTFSA have been calculated to be 0.23, 0.38, and 0.12 nm, from the diffusion coefficients and viscosities obtained. 相似文献