首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
侯万国  REN Carolyn 《中国化学》2006,24(10):1336-1341
The intrinsic surface reaction constants, pKa1^int, pKa2^int, p^*KC^int and p^*KA^int , were evaluated by a modifieddouble extrapolation (MDE) for TiO2 without structural charge and Mg-Fe hydrotalcite-like compounds (HTlc) with structural charge, respectively. The results of intrinsic surface reaction constants for TiO2 were compared with those obtained by class double extrapolation (CDE) in literature. Furthermore, the values of intrinsic surface reaction constants obtained by MDE were used to simulate the charging behaviors of the materials. The following conclusions were obtained. For TiO2 without structural charge, the pKa1^int and pKa2^int evaluated by MDE are equal to those by CDE, however the p^*KC^int and p^*KA^int evaluated by MDE are much different from those by CDE. In principle, the results of the p^*KC^int and p^*KA^int evaluated by MDE are more accurate than those by CDE. The values of intrinsic surface reaction constants obtained by MDE can excellently simulate the charging curves for TiO2 with the triple layer model (TLM). For HTlc with positive structural charge, the results of ^*KC^int=0 and ^*KA^int →∞ were obtained by MDE, which means the inert electrolyte chemical binding does not exist; the point of zero net charge (PZNC) of c-independence also exist as the same as solid without structural charge, and the PHPZNC obtained by the acid-base titration can excellently be simulated and the surface charging tendency can be simulated to a great extent using the pKa1^int and pKa2^int evaluated by MDE and the diffuse layer model (DLM).  相似文献   

2.
The generation of metastable O2(1Σg+) and O2(1Δg) in the H + O2 system of reactions was studied by the flow discharge chemiluminescence detection method. In addition to the O2(1Σg+) and O2(1Δg) emissions, strong OH(v = 2) → OH(v = 0), OH(v = 3) → OH(v = 1), HO2(2A000) → HO2(2A000), HO2(2A001) → HO2(2A000), and H O2(2A200) → HO2(2A000) emissions were detected in the H + O2 system. The rate constants for the quenching of O2(1Σg+) by H and H2 were determined to be (5.1 ± 1.4) × 10?13 and (7.1 ± 0.1) × 10?13 cm3 s?1, respectively. An upper limit for the branching ratio to produce O2(1Σg+) by the H + HO2 reaction was calculated to be 2.1%. The contributions from other reactions producing singlet oxygen were investigated.  相似文献   

3.
Using atomic beam technique, a combination of collisional and laser excitation, and photoion detection, autoionizing Cu I states in the region of the ionization limits Cu II 3d 9 4s(3,1 D) were investigated. In spite of the complicated structure of the signals due to the four different ionization limits3 D 3,3 D 2,3 D 1 and1 D 2 and the large number of possible (LSJ)-states, which can be reached by this experimental technique, the majority of the signals could be attributed to definite Rydberg series 3d 9 4s(3 D 3,3 D 2,3 D 1,1 D 2)nl (LSJ). Perturbations were analyzed by the three- and four-channel quantum defect theory and by Hartree-Fock calculations. General formulas for the calculation of the photoionization cross section by the four-channel quantum defect theory in the case of two closed and two open channels are given.  相似文献   

4.
The design and synthesis of functional coordination polymers is motivated not only by their structural beauty but also by their potential applications. ZnII and CdII coordination polymers are promising candidates for producing photoactive materials because these d10 metal ions not only possess a variety of coordination numbers and geometries, but also exhibit luminescence properties when bound to functional ligands. It is difficult to predict the final structure of such polymers because the assembly process is influenced by many subtle factors. Bis(imidazol‐1‐yl)‐substituted alkane/benzene molecules are good bridging ligands because their flexibility allows them to bend and rotate when they coordinate to metal centres. Two new ZnII and CdII coordination polymers based on mixed ligands, namely, poly[[μ2‐1,4‐bis(imidazol‐1‐ylmethyl)benzene‐κ2N3:N3′]bis(μ3‐2,2‐dimethylbutanoato‐κ3O1:O4:O4′)dizinc(II)], [Zn2(C6H8O4)2(C14H14N4)]n, and poly[[μ2‐1,4‐bis(imidazol‐1‐ylmethyl)benzene‐κ2N3:N3′]bis(μ3‐2,2‐dimethylbutanoato‐κ5O1,O1′:O4,O4′:O4)dicadmium(II)], [Cd2(C6H8O4)2(C14H14N4)]n, have been synthesized under hydrothermal conditions and characterized by single‐crystal X‐ray diffraction, elemental analysis, IR spectroscopy and thermogravimetric analysis. Both complexes crystallize in the monoclinic space group C2/c with similar unit‐cell parameters and feature two‐dimensional structures formed by the interconnection of S‐shaped Zn(Cd)–2,2‐dimethylsuccinate chains with 1,4‐bis(imidazol‐1‐ylmethyl)benzene bridges. However, the CdII and ZnII centres have different coordination numbers and the 2,2‐dimethylsuccinate ligands display different coordination modes. Both complexes exhibit a blue photoluminescence in the solid state at room temperature.  相似文献   

5.
Sesquialkoxides of Gallium and Indium Treatment of GaMe3 with one equivalent of HOcHex in toluene at 20 °C leads to [Me2GaOcHex]2 ( 4 ) under evolution of methane. The reaction of InMe3 with two equivalents of HOcHex leads under similar conditions not to [MeIn(OcHex)2]n but to the sesquialkoxide [In{Me2In(OcHex)2}3] ( 5 ). 5 can be described also as [{Me2InOcHex)}2{MeIn(OcHex)2}2]. The use of an excess of cyclohexanol in boiling toluene gives the same result. Under these reflux conditions, the reaction of GaMe3 with an excess of PhCH2OH leads exclusively to another type of sequialkoxides, [Ga{MeGa(OCH2Ph)3}3] ( 6 ). 4 — 6 were characterized by NMR, vibrational and MS spectra, as well as by X‐ray structure determinations. According to this, 4 forms centrosymmetrical and therefore planar Ga2O2 four‐membered rings. 5 and 6 possess basically the same structural motif, central M3+ ion ( 5 : In3+; 6 : Ga3+) coordinated by three metalate units ( 5 : [Me2In(OcHex)2]; 6 : [MeGa(OCH2Ph)3]). The central M3+ ions have always coordination number (CN) six while the three surrounding metal ions possess CN 4. Because of the spectroscopic findings 6 must exist in two isomers (1:1). The C3‐symmetrical isomer C3‐ 6 was characterized by X‐ray analysis, while the isomer C1‐ 6 could by described mainly by the complex NMR data.  相似文献   

6.
In order to explore new metal coordination polymers and to search for new types of ferroelectrics among hybrid coordination polymers, two manganese dicyanamide complexes, poly[tetramethylammonium [di‐μ3‐dicyanamido‐κ6N1:N3:N5‐tri‐μ2‐dicyanamido‐κ6N1:N5‐dimanganese(II)]], {[(CH3)4N][Mn2(NCNCN)5]}n, (I), and catena‐poly[bis(butyltriphenylphosphonium) [[(dicyanamido‐κN1)manganese(II)]‐di‐μ2‐dicyanamido‐κ4N1:N5]], {[(C4H9)(C6H5)3P]2[Mn(NCNCN)4]}n, (II), were synthesized in aqueous solution. In (I), one MnII cation is octahedrally coordinated by six nitrile N atoms from six anionic dicyanamide (dca) ligands, while the second MnII cation is coordinated by four nitrile N atoms and two amide N atoms from six anionic dca ligands. Neighbouring MnII cations are linked together by μ‐1,5‐ and μ‐1,3,5‐bridging dca anions to form a three‐dimensional polymeric structure. The anionic framework exhibits a solvent‐accessible void of 289.8 Å3, amounting to 28.0% of the total unit‐cell volume. Each of the cavities in the network is occupied by only one tetramethylammonium cation. In (II), each MnII cation is octahedrally coordinated by six nitrile N atoms from six dca ligands. Neighbouring MnII cations are linked together by double dca bridges to form a one‐dimensional polymeric chain, and C—H...N hydrogen‐bonding interactions are involved in the formation of the one‐dimensional layer structure.  相似文献   

7.
Sunlight‐excitable orange or red persistent oxide phosphors with excellent performance are still in great need. Herein, an intense orange‐red Sr3?xBaxSiO5:Eu2+,Dy3+ persistent luminescence phosphor was successfully developed by a two‐step design strategy. The XRD patterns, photoluminescence excitation and emission spectra, and the thermoluminescence spectra were investigated in detail. By adding non‐equivalent trivalent rare earth co‐dopants to introduce foreign trapping centers, the persistent luminescence performance of Eu2+ in Sr3SiO5 was significantly modified. The yellow persistent emission intensity of Eu2+ was greatly enhanced by a factor of 4.5 in Sr3SiO5:Eu2+,Nd3+ compared with the previously reported Sr3SiO5:Eu2+, Dy3+. Furthermore, Sr ions were replaced with equivalent Ba to give Sr3?xBaxSiO5:Eu2+,Dy3+ phosphor, which shows yellow‐to‐orange‐red tunable persistent emissions from λ=570 to 591 nm as x is increased from 0 to 0.6. Additionally, the persistent emission intensity of Eu2+ is significantly improved by a factor of 2.7 in Sr3?xBaxSiO5:Eu2+,Dy3+ (x=0.2) compared with Sr3SiO5:Eu2+,Dy3+. A possible mechanism for enhanced and tunable persistent luminescence behavior of Eu2+ in Sr3?xBaxSiO5:Eu2+,RE3+ (RE=rare earth) is also proposed and discussed.  相似文献   

8.
The title coordination polymer, poly[(μ4‐2‐oxidoisophthalato‐κ6O1,O2:O2,O3:O3′:O3′)(μ2‐quinoxaline‐κ2N:N′)copper(I)copper(II)], [Cu2(C8H3O5)(C8H6N2)]n, contains two crystallographically distinct Cu ions, one quinoxaline (QA) unit and one 2‐oxidoisophthalate trianion (L) derived from 2‐hydroxyisophthalic acid (H3L). The CuII ion is strongly coordinated by four O atoms in a distorted square geometry, of which two belong to two phenoxide groups and the other two to carboxylate groups of two L ligands. In addition, the CuII cation interacts weakly with a symmetry‐related carboxylate O atom which belongs to the L ligand in an adjacent layer, giving a square‐pyramidal coordination geometry. The CuI ion is trigonally coordinated by two N atoms from two QA molecules and one O atom from an L carboxylate group. The CuI centres are bridged by QA ligands to give a chain along the c axis. Two CuII ions and two L ligands form a [Cu2L2]2− `metallo‐ligand', which coordinates two CuI ions. Thus, the chains of CuI and QA are linked by the [Cu2L2]2− metallo‐ligand to yield a two‐dimensional (6,3) sheet. These sheets are further linked by symmetry‐related carboxylate O atoms of neighbouring layers into a three‐dimensional framework. The in situ reaction from benzene‐1,2,3‐tricarboxylic acid (H3L1) to L in the present system has rarely been observed before, although a few novel in situ reactions, such as ligand oxidative coupling, hydrolysis and substitution, have been observed during the hydrothermal process.  相似文献   

9.
The complex Young's modulus, E*(ω), and the complex strain-optical coefficient, O*(ω), which is the ratio of the birefringence to the strain, were measured for polyisoprene (PIP) over a frequency range of 1 ~ 130 Hz and a temperature range of 22 ~ ?100°C. The imaginary part of O*, O″, was positive at low frequencies and negative at high frequencies. The real part, O′, was always positive and showed a maximum. The complicated behavior of O* could be understood by the assumption that E* = ER* + EG* and O* = CRER* + CGEG*, where ER* and EG* were complex quantities and CR and CG were constants. The CR value, equal to the ordinary stress-optical coefficient measured in the rubbery plateau zone, was 2.0 × 10?9 Pa?1. The CG value, defined as the ratio O″/E″ in the glassy zone, was ?1.1 × 10?11 Pa?1. The EG*, which was the major component of E* in the glassy zone, showed almost the same frequency dependence as that of polystyrene and polycarbonate. The ER*, which was dominant in the rubbery zone, was described well by the bead-spring theory. The temperature dependence of the EG* was stronger than that of the ER*. This difference caused the breakdown of the thermorheological simplicity for E* and O* around the glass-to-rubber transition zone. © 1995 John Wiley & Sons, Inc.  相似文献   

10.
The trans‐bis(trimethylsilyl)chalcogenolate palladium complexes, trans‐[Pd(ESiMe3)2(PnBu3)2] [E = S ( 1 ) and Se ( 2 )] were synthesized in good yields and high purity by reacting trans‐[PdCl2(PBu3)2] with LiESiMe3 (E = S, Se), respectively. These complexes were characterized by 1H, 13C{1H}, 31P{1H} (and 77Se{1H}) NMR spectroscopy and single‐crystal X‐ray analysis. The reaction of 2 with propionyl chloride led to the formation of trans‐[Pd(SeC(O)CH2CH3)2(PnBu3)2] ( 3 ), a trans‐bis(selenocarboxylato) palladium complex and thus established a new method for the formation of this type of complex. Complex 3 was characterized by 1H, 13C{1H}, 31P{1H} and 77Se{1H} NMR spectroscopy and a single‐crystal X‐ray structure analysis.  相似文献   

11.
A dicationic triruthenium complex containing a μ3-η3-C3 ring, [(Cp*Ru)3(μ3-η3-C3MeH2−)(μ3-CH)(μ-H)]2+ ( 1 a , Cp*=η5-C5Me5), reacted with ammonia to yield a μ-amido complex, [(Cp*Ru)33-η3-CHCMeCH) (μ3-CH)(μ-NH2)]2+ ( 5 ), via N−H bond scission. Subsequent treatment with base resulted in C−N bond formation to yield a μ3-η2:η2-1-azabutadien-4-yl complex, [(Cp*Ru)3(μ3-CH)(μ3-η2:η2-NH=CH−CMe=CH−)]+ ( 6 a ). The azaruthenacyclopentadiene skeleton was alternatively synthesized by the photolysis of mono-cationic complex [(Cp*Ru)3(μ3-η3-C3RH2−)(μ3-CH)]+ ( 2 a ; R=Me, 2 b ; R=H) in the presence of ammonia. The C3 ring skeleton was broken via the electron transfer to the π*(C−C) orbital in the C3 ring, and a transiently generated unsaturated μ3-allylic species can take up ammonia, resulting in N−H bond scission followed by C−N bond formation.  相似文献   

12.
A new series of cationic heterodinuclear complexes, [M1M2Cl2(meso-dpmppp)(RNC)2]PF6 (M1=Ni, M2=Rh, R=tBu ( 1 a ); M1=Pd, M2=Rh, R=tBu ( 2 a ), Xyl ( 2 b ); M1=Pt, M2=Rh, R=tBu ( 3 a ), Xyl ( 3 b ); M1=Pd, M2=Ir, R=tBu ( 4 a )), supported by a tetradentate phosphine ligand, meso-Ph2PCH2P(Ph)(CH2)3P(Ph)CH2PPh2 (meso-dpmppp), were synthesized by stepwise reactions of meso-dpmppp with NiCl2 ⋅ 6H2O or MCl2(cod) (M=Pd, Pt), forming mononuclear metalloligands of [M1Cl2(meso-dpmppp)], and with [M2Cl(cod)]2 (M2=Rh, Ir) and RNC (R=tBu, Xyl) in the presence of [NH4][PF6]. The related neutral PdRh complex, [PdRhCl3(meso-dpmppp)(XylNC)] ( 5 ), was also prepared. The structures of 1 – 5 were determined by X-ray analyses to contain two square planar d8 metal centers with face-to-face arrangement, where meso-dpmppp supports M1 and M2 metal ions in cis/trans-P,P coordination mode, combining cis-{M1P2Cl2} and trans-{M2P2(CNR)2} units. Complexes 1 – 4 showed an intence characteristic absorption around 422–464 nm derived from RhI→RNC MLCT transition (HOMO→LUMO+1), which are influenced by changing M1 (NiII, PdII, PtII) metal ions since HOMO composed of dσ* orbitals appreciably destabilized by changing M1 from Ni to Pd, and Pt. The electronic structures of 1 a – 4 a were investigated on the basis of DFT calculations and NBO analyses to show weak but noticeable d8–d8 metallophilic interaction as empirical dispersion energy of 0.9–1.5 kcal/mol without M1–M2 covalent bonding interaction. In addition, 1 – 5 were utilized as catalysts for hydrosilylation of styrene, and the NiRh complex 1 a was found to show higher activity and chemo- and regioselectivity compared with 2 – 5 .  相似文献   

13.
Equilibria concerning picrates of tetraalkylammonium ions (Me4N+, Et4N+, Pr4N+, Bu4N+, Bu3MeN+) in a dichloromethane−water system have been investigated at 25 C. The 1:1 ion-pair formation constants (K IP,o o) in dichloromethane at infinite dilution were conductometrically determined. The distribution constants (K D o) of the ion pairs and the free cations between the solvents were determined by a batch-extraction method. The K IP,o o value varies in the cation sequence, Bu4N+ ≈ Pr4N+ ≈ Et4N+ < Bu3MeN+ < < Me4N+; this trend is explained by the electrostatic cation−anion interaction taking into account the structures of the ion pairs determined by density functional theory calculations. For the ion pairs of the symmetric R4N+ cations, there is a linear positive relationship between log10 K D o and the number of methylene groups in the cation (N CH 2). The ion pair of asymmetric Bu3MeN+ has a higher distribution constant than that expected from the above log10 K D o versus N CH 2 relationship. These cation dependencies of log10 K D o for the ion pairs are explained theoretically by using the Hildebrand-Scatchard equation. For all the cations, the log10 K D o value of the free cation increases linearly with N CH 2; the variation of log10 K D o is discussed by decomposing the distribution constant into the Born-type electrostatic contribution and the non-Born one, and attributed to the latter that is governed by the differences in the molar volumes of the cations. The cation dependencies of the ion-pair extractability and ion pairing in water are also discussed. An erratum to this article can be found at  相似文献   

14.
‘Bare’ FeO+ reacts in the gas phase with norbornane with collision efficiency, and the most prominent cationic products correspond to [FeC5H6]+ (32%), [FeC7H8]+ (19%), [FeC3H6O]+ (19%) and [FeC6H6]+ (14%), which are structurally characterized by ligand exchange as well as collision-induced dissociation experiments. Circumstantial evidence is provided which indicates that the complexes [FeC5H6]+, [FeC7H8]+, and [FeC6H6]+ originate from an Fe(norbornene)+ intermediate which itself is formed by elimination of H2O from the [FeO(norbornane)]+ encounter complex. Although the reactions are preceded and/or accompanied by partial H/D exchange, the isotope distribution in the productions clearly points to a preferential endo-attack of bare FeO+, with an endo/exo-ratio of ca. 10.3 and kinetic isotope effects kH/kD for the endo-abstraction of 2.4 and of 7.7 for approaching an exo-C? H bond. The preferred endo-approach of bicyclo[2.2.1]heptane by ‘bare’ FeO+ is in distinct contrast to the P-450-mediated or the iron(III)porphyrin-catalyzed hydroxylation of this substrate which favor reactions at the exo-face.  相似文献   

15.
Multireference configuration interaction wave functions with single and double excitations were calculated for the 1Σ+g ground state of the C2 molecule and the excited states of C+2 with symmetries 2Σ+g, 2Σ-u, 2Πu, and 2Πg. The corresponding σg, σu, πu, and πg valence Dyson orbitals were calculated. Most of the density due to the valence electrons is accounted for by three σg, one σu, and one degenerate pair of πu Dyson orbitals. Electron correlation plays an important role in the bond strength of C2 by increasing the occupation of the σg valence orbitals and decreasing the occupation of the σu and πu valence orbitals. © 1996 John Wiley & Sons, Inc.  相似文献   

16.
The activation of C?H bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O?.) is an important species in C?H activation. The mechanistic details of C?H activation by O?. radicals can be well understood by studying the reactions between O?. containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n‐butane was studied by using a high‐resolution time‐of‐flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n‐butane by (Sc2O3)NO? (N=1–18) clusters was observed. The reactivity of (Sc2O3)NO? (N=1–18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc8O13?) and 12 (Sc24O37?). Larger (Sc2O3)NO? clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc2O3)NO? (N=1–5) clusters, which were found to contain the O?. radicals as the active sites. The local charge environment around the O?. radicals was demonstrated to control the experimentally observed size‐dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O?. containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the C?H bond activation.  相似文献   

17.
Abstract

An environmentally benign hydrolysis of methylphenyldiethoxysilane (MePhSi(OEt)2) catalyzed by a rare earth superacid catalyst SO 2? 4 /TiO2/Ln3+ has been investigated. The hydrolysis rates decrease in the order SO 2? 4 /TiO2/Nd3+ > SO 2? 4 /TiO2/Y3+ > SO 2? 4 /TiO2/Sm3+ > SO 2? 4 /TiO2. The hydrolysis of MePhSi(OEt)2 is a first-order reaction with respect to the concentration of MePhSi(OEt)2, and the hydrolysis rate constant increases with increasing temperature. The activation energy E a and the pre-exponential factor for this hydrolysis catalyzed by SO 2? 4 /TiO2/Nd3+ have been determined as 322.50 kJ mol?1 and 7.12 × 1041 s?1, respectively. The products of the hydrolysis are oligomers of polymethylphenylsiloxane. The mechanism of MePhSi(OEt)2 hydrolysis is also discussed.  相似文献   

18.
Two cadmium halide complexes, catena‐poly[[chloridocadmium(II)]‐di‐μ‐chlorido‐[chloridocadmium(II)]‐bis[μ2‐4‐(dimethylamino)pyridin‐1‐ium‐1‐acetate]‐κ3O:O,O′;κ3O,O′:O], [CdCl2(C9H12N2O2)]n, (I), and catena‐poly[1‐cyanomethyl‐1,4‐diazoniabicyclo[2.2.2]octane [[dichloridocadmium(II)]‐μ‐oxalato‐κ4O1,O2:O1′,O2′] monohydrate], {(C8H15N3)[CdCl2(C2O4)]·H2O}n, (II), were synthesized in aqueous solution. In (I), the CdII cation is octahedrally coordinated by three O atoms from two carboxylate groups and by one terminal and two bridging chloride ligands. Neighbouring CdII cations are linked together by chloride anions and bridging O atoms to form a one‐dimensional zigzag chain. Hydrogen‐bond interactions are involved in the formation of the two‐dimensional network. In (II), each CdII cation is octahedrally coordinated by four O atoms from two oxalic acid ligands and two terminal Cl ligands. Neighbouring CdII cations are linked together by oxalate groups to form a one‐dimensional anionic chain, and the water molecules and organic cations are connected to this one‐dimensional zigzag chain through hydrogen‐bond interactions.  相似文献   

19.
X‐ray diffraction analysis of single crystals of three new arsenates adopting apatite‐type structures yielded formula Sr5(AsO4)3F for strontium arsenate fluoride, (I), (Sr1.66Ba0.34)(Ba2.61Sr0.39)(AsO4)3Cl for strontium barium arsenate chloride, (II), and Cd5(AsO4)3Cl0.58(OH)0.42 for cadmium arsenate hydroxide chloride, (III). All three structures are built up of isolated slightly distorted AsO4 tetrahedra that are bridged by Sr2+ in (I), by Sr2+/Ba2+ in (II) and by Cd2+ in (III). Compounds (I) and (II) represent typical fluorapatites and chlorapatites, respectively, with F at the 2a (0, 0, ) site and Cl at the 2b (0, 0, 0) site of P63/m. In contrast, in (III), due to the requirement that the smaller Cd2+ cation is positioned closer to the channel Cl anion (partially substituted by OH), the anion occupies the unusual 2a (0, 0, ) site. Therefore, Cl is similar to F in (I), coordinated by three A2 cations, unlike the octahedrally coordinated Cl in (II) and other ordinary chlorapatites. Furthermore, in (III), using FT–IR studies, we have inferred the existence of H+ outside the channel in oxyhydroxyapatites and provided possible atomic coordinates for a H atom in HAsO42−, leading to a proposed formulation of the compound as Cd5(AsO4)3−x(HAsO4)xCl0.58(OH)0.42−x−(y/2)Ox+(y/2)y/2.  相似文献   

20.
The 13C NMR spectra of 23 2,3-dihydro-1H-benzo[b]azepines, including nine pairs of diastereomers separated by chromatography, [(2R*, 3R*) and (2R*), 3S*)] are hereby assigned and discussed. The relative configurations of the diastereomers were assigned by two methods. The first, based on the chemical shifts of the asymmetric carbons C-2 and C-3 (with regression analysis), shows that the values for (R*, R*) are approximately 1 ppm lower than those for (R*, S*) diastereomers. The second method uses the chemical shifts, δ3, of the R3(CH3) substituents. When these δ3 values are compared by means of the δ3m difference (δm is the mean value obtained from compounds where R2=H), the difference is always negative for (R*, R*) and positive for (R*, S*). This is attributed to a γ-gauche effect between R2 and R3 in the case of (R*, R*) diastereomers (R2 and R3 are cis). The results corroborate those already obtained by 1H NMR [J(23)(R*, R*)<J(23)(R*, S*)] and are a confirmation of the results of a radiocrystallographic examination carried out on two nitrogen acetylated diastereomers.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号