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1.
Pd-catalyzed double carbomethoxylation of the Diels-Alder adduct of cyclo-pentadiene and maleic anhydride yielded the methyl norbornane-2,3-endo-5, 6-exo-tetracarboxylate ( 4 ) which was transformed in three steps into 2,3,5,6-tetramethyl-idenenorbornane ( 1 ). The cycloaddition of tetracyanoethylene (TCNE) to 1 giving the corresponding monoadduct 7 was 364 times faster (toluene, 25°) than the addition of TCNE to 7 yielding the bis-adduct 9 . Similar reactivity trends were observed for the additions of TCNE to the less reactive 2,3,5,6-tetramethylidene-7-oxanorbornane ( 2 ). The following second order rate constants (toluene, 25°) and activation parameters were obtained for: 1 + TCNE → 7 : k1 = (255 + 5) 10?4 mol?1 · s?1, ΔH≠ = (12.2 ± 0.5) kcal/mol, ΔS≠ = (?24.8 ± 1.6) eu.; 7 + TCNE → 9 , k2 = (0.7 ± 0.02) 10?4 mol?1 · s?1, ΔH≠ = (14.1 ± 1.0) kcal/mol, ΔS≠ = ( ?30 ± 3.5) eu.; 2 + TCNE → 8 : k1 = (1.5 ± 0.03) 10?4 mol?1 · s?1, ΔH≠ = (14.8 ± 0.7) kcal/mol, ΔS≠ = (?26.4 ± 2.3) eu.; 8 + TCNE → 10 ; k2 = (0.004 ± 0.0002) 10?4 mol?1 · s?1, ΔH≠ = (17 ± 1.5) kcal/mol, ΔS≠ = (?30 ± 4) eu. The possible origins of the relatively large rate ratios k1/k2 are discussed briefly.  相似文献   

2.
The [2.2.2]hericene ( 6 ), a bicyclo[2.2.2]octane bearing three exocyclic s-cis-butadiene units has been prepared in eight steps from coumalic acid and maleic anhydride. The hexaene 6 adds successively three mol-equiv. of strong dienophiles such as ethylenetetracarbonitrile (TCE) and dimethyl acetylenedicarboxylate (DMAD) giving the corresponding monoadducts 17 and 20 (k1), bis-adducts 18 and 21 (k2) and tris-adducts 19 and 22 (k3), respectively. The rate constant ratio k1/k2 is small as in the case of the cycloadditions of 2,3,5,6-tetramethylidene-bicyclo [2.2.2]octane ( 3 ) giving the corresponding monoadducts 23 and 27 (k1) and bis-adducts 25 and 29 (k2) with TCE and DMAD, respectively. Constrastingly, the rate constant ratio k2/k3 is relatively large as the rate constant ratio k1/k2 of the Diels-Alder additions for 5,6,7,8-tetramethylidenebicyclo [2.2.2]oct-2-ene ( 4 ) giving the corresponding monoadducts 24 and 28 (k1) and bis-adducts 26 and 30 (k2). The following second-order rate constants (toluene, 25°) and activation parameters were obtained for the TCE additions: 3 +TCE→ 23 : k1 = 0.591±0.012 mol?1·l·s?1, ΔH=10.6±0.4 kcal/mol, and ΔS = ?24.0±1.4 cal/mol·K (e.u.); 23 +TCE→ 25 : k2=0.034±0.0010 mol?1·l·s?1, ΔH = 10.6±0.6 kcal/mol, and ΔS = ?29.7±2.0 e.u.; 4 +TCE→ 26 : k1 = 0.172±0.035 mol?1·l·s?1, ΔH 11.3±0.8 kcal/mol, and ΔS = ?24.0±2.8 e.u.; 24 +TCE→ 26 : k2 = (6.1±0.2)·10?4 mol?1·l·s?1, ΔH = 13.0±0.3 kcal/mol, and ΔS = ?29.5±0.8 e.u.; 6 +TCE→ 17 : k1 = 0.136±0.002 mol?1·l·s?1, ΔH = 11.3±0.2 kcal/mol, and ΔS = ?24.5±0.8 e.u.; 17 +TCE→ 18 : k2 = 0.0156±0.0003 mol?1·l·s?1, ΔH = 10.9±0.5 kcal/mol, and ΔS = ?30.1 ± 1.5 e.u.; 18 +TCE→ 19 : k3=(5±0.2) · 10?5 mol?1 mol?1 ·l·s?1, ΔH = 15±3 kcal/mol, and ΔS = ?28 ± 8 e.u. The following rate constants were evaluated for the DMAD additions (CD2Cl2, 30°): 6 +DMAD→ 20 : k1 = (10±1)·10?4 mol?1 · l·s?1; 20 +DMAD→ 21 : k2 = (6.5±0.1) · 10?4 mol?1 ·l·?1; 21 +DMAD→ 22 : k3 = (1.0±0.1) · 10?4 mol?1 ·l·s?1. The reactions giving the barrelene derivatives 19, 22, 26 and 30 are slower than those leading to adducts that are not barrelenes. The former are estimated less exothermic than the latter. It is proposed that the Diels-Alder reactivity of exocyclic s-cis-butadienes grafted onto bicycle [2.2.1]heptanes and bicyclo [2.2.2]octanes that are modified by remote substitution of the bicyclic skeletons can be affected by changes inthe exothermicity of the cycloadditions, in agreement with the Dimroth and Bell-Evans-Polanyi principle. Force-field calculations (MMPI 1) of 3, 4, 6 and related exocyclic s-cis-butadienes as a moiety of bicyclo [2.2.2]octane suggested single minimum energy hypersurfaces for these systems (eclipsed conformations, planar dienes). Their flexibility decreases with the degree of unsaturation of the bicyclic skeleton. The effect of an endocyclic double bond is larger than that of an exocyclic diene moiety.  相似文献   

3.
At room temperature and below, the proton NMR spectrum of N-(trideuteriomethyl)-2-cyanoaziridine consists of two superimposed ABC patterns assignable to two N-invertomers; a single time-averaged ABC pattern is observed at 158.9°C. The static parameters extracted from the spectra in the temperature range from –40.3 to 23.2°C and from the high-temperature spectrum permit the calculation of the thermodynamic quantities ΔH0 = ?475±20 cal mol?1 (?1.987 ± 0.084 kJ mol?1) and ΔS0 = 0.43±0.08 cal mol?1 K?1 (1.80±0.33 J mol?1 K?1) for the cis ? trans equilibrium. Bandshape analysis of the spectra broadened by non-mutual three-spin exchange in the temperature range from 39.4–137.8°C yields the activation parameters ΔHtc = 17.52±0.18 kcal mol?1 (73.30±0.75 kJ mol?1), ΔStc = ?2.08±0.50 cal mol?1 K?1 (?8.70±2.09 J mol?1 K?1) and ΔGtc (300 K) = 18.14±0.03 kcal mol?1 (75.90±0.13 kJ mol?1) for the transcis isomerization. An attempt is made to rationalize the observed entropy data in terms of the principles of statistical thermodynamics.  相似文献   

4.
The oxidation of Na4Fe(CN)6 complex by S2O anion was found to follow an outer‐sphere electron transfer mechanism. We firstly carried out the reaction at pH=1. The specific rate constants of the reaction, kox, are (8.1±0.07)×10?2 and (4.3±0.1)×10?2 mol?1·L·s?1 at μ=1.0 mol·L?1 NaClO4, T=298 K for pH=1 (0.1 mol·L?1 HCl04) and 8, respectively. The activation parameters, obtained by measuring the rate constants of oxidation 283–303 K, were ΔH=(69.0±5.6) kJ·mol?1, ΔS=(?0.34±0.041)×102 J·mol?1·K?1 at pH=l and ΔH=(41.3±5.5) kJ·mol?1, ΔS=(?1.27±0.33)×102 J·mol?1·K?1 at pH=8, respectively. The cyclic voltammetry of Fe(CN) shows that the oxidation is a one‐electron reversible redox process with E1/2 values of 0.55 and 0.46 V vs. normal hydrogen electrode at μ=1.0 mol·L?1 LiClO4, for pH=1 and pH=8 (Tris). respectively. The kinetic results were discussed on the basis of Marcus theory.  相似文献   

5.
L-脯氨酸独有的亚胺基使其在生物医药领域具有许多独特的功能,并广泛用作不对称有机化合物合成的有效催化剂。本文在碱性介质中研究了二(氢过碘酸)合银(III)配离子氧化 L-脯氨酸的反应。经质谱鉴定,脯氨酸氧化后的产物为脯氨酸脱羧生成的 γ-氨基丁酸盐;氧化反应对脯氨酸及Ag(III) 均为一级;二级速率常数 k′ 随 [IO4-] 浓度增加而减小,而与 [OHˉ] 的浓度几乎无关;推测反应机理应包括 [Ag(HIO6)2]5-与 [Ag(HIO6)(H2O)(OH)]2-之间的前期平衡,两种Ag(III)配离子均作为反应的活性组分,在速控步被完全去质子化的脯氨酸平行地还原,两速控步对应的活化参数为: k1 (25 oC)=1.87±0.04(mol·L-1)-1s-1,∆ H1=45±4 kJ · mol-1, ∆ S1=-90±13 J· K-1·mol-1 and k2 (25 oC) =3.2±0.5(mol·L-1)-1s-1, ∆ H2=34±2 kJ · mol-1, ∆ S2=-122 ±10 J· K-1·mol-1。本文第一次发现 [Ag(HIO6)2]5-配离子也具有氧化反应活性。  相似文献   

6.
The E and Z geometric isomers of a stable silene (tBu2MeSi)(tBuMe2Si)Si=CH(1‐Ad) ( 1 ) were synthesized and characterized spectroscopically. The thermal Z to E isomerization of 1 was studied both experimentally and computationally using DFT methods. The measured activation parameters for the 1Z ? 1E isomerization are: Ea=24.4 kcal mol?1, ΔH=23.7 kcal mol?1, ΔS=?13.2 e.u. Based on comparison of the experimental and DFT calculated (at BP86‐D3BJ/def2‐TZVP(‐f)//BP86‐D3BJ/def2‐TZVP(‐f)) activation parameters, the Z?E isomerization of 1 proceeds through an unusual (unprecedented for alkenes) migration–rotation–migration mechanism (via a silylene intermediate), rather than through the classic rotation mechanism common for alkenes.  相似文献   

7.
The kinetics of the interactions between three sulfur‐containing ligands, thioglycolic acid, 2‐thiouracil, glutathione, and the title complex, have been studied spectrophotometrically in aqueous medium as a function of the concentrations of the ligands, temperature, and pH at constant ionic strength. The reactions follow a two‐step process in which the first step is ligand‐dependent and the second step is ligand‐independent chelation. Rate constants (k1 ~10?3 s?1 and k2 ~10?5 s?1) and activation parameters (for thioglycolic acid: ΔH1 = 22.4 ± 3.0 kJ mol?1, ΔS1 = ?220 ± 11 J K?1 mol?1, ΔH2 = 38.5 ± 1.3 kJ mol?1, ΔS2 = ?204 ± 4 J K?1 mol?1; for 2‐thiouracil: ΔH1 = 42.2 ± 2.0 kJ mol?1, ΔS1 = ?169 ± 6 J K?1 mol?1, ΔH2 = 66.1 ± 0.5 kJ mol?1, ΔS2 = ?124 ± 2 J K?1 mol?1; for glutathione: ΔH1 = 47.2 ± 1.7 kJ mol?1, ΔS1 = ?155 ± 5 J K?1mol?1, ΔH2 = 73.5 ± 1.1 kJ mol?1, ΔS2 = ?105 ± 3 J K?1 mol?1) were calculated. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. The products of the reactions have been characterized from IR and ESI mass spectroscopic analysis. A rate law involving the outer sphere association complex formation has been established as   相似文献   

8.
The pterin‐coordinated ruthenium complex, [RuII(dmdmp)(tpa)]+ ( 1 ) (Hdmdmp=N,N‐dimethyl‐6,7‐dimethylpterin, tpa=tris(2‐pyridylmethyl)amine), undergoes photochromic isomerization efficiently. The isomeric complex ( 2 ) was fully characterized to reveal an apparent 180° pseudorotation of the pterin ligand. Photoirradiation to the solution of 1 in acetone with incident light at 460 nm resulted in dissociation of one pyridylmethyl arm of the tpa ligand from the RuII center to give an intermediate complex, [Ru(dmdmp)(tpa)(acetone)]2+ ( I ), accompanied by structural change and the coordination of a solvent molecule to occupy the vacant site. The quantum yield (?) of this photoreaction was determined to be 0.87 %. The subsequent thermal process from intermediate I affords an isomeric complex 2 , as a result of the rotation of the dmdmp2? ligand and the recoordination of the pyridyl group through structural change. The thermal process obeyed first‐order kinetics, and the rate constant at 298 K was determined to be 5.83×10?5 s?1. The activation parameters were determined to be ΔH=81.8 kJ mol?1 and ΔS=?49.8 J mol?1 K?1. The negative ΔS value indicates that this reaction involves a seven‐coordinate complex in the transition state (i.e., an interchange associative mechanism). The most unique point of this reaction is that the recoordination of the photodissociated pyridylmethyl group occurs only from the direction to give isomer 2 , without going back to starting complex 1 , and thus the reaction proceeds with 100 % conversion efficiency. Upon heating a solution of 2 in acetonitrile, isomer 2 turned back into starting complex 1 . The backward reaction is highly dependent on the solvent: isomer 2 is quite stable and hard to return to 1 in acetone; however, 2 was converted to 1 smoothly by heating in acetonitrile. The activation parameters for the first‐order process in acetonitrile were determined to be ΔH=59.2 kJ mol?1 and ΔS=?147.4 kJ mol?1 K?1. The largely negative ΔS value suggests the involvement of a seven‐coordinate species with the strongly coordinated acetonitrile molecule in the transition state. Thus, the strength of the coordination of the solvent molecule to the RuII center is a determinant factor in the photoisomerization of the RuII–pterin complex.  相似文献   

9.
The kinetics of the interaction of L ‐asparagine with [Pt(ethylenediamine)(H2O)2]2+ have been studied spectrophotometrically as a function of [Pt(ethylenediamine)(H2O)22+], [L ‐asparagine], and temperature at pH 4.0, where the substrate complex exists predominantly as the diaqua species and L ‐asparagine as the zwitterion. The substitution reaction shows two consecutive steps: the first step is the ligand‐assisted anation and the second one is the chelation step. Activation parameters for both the steps have been calculated using Eyring equation. The low ΔH1 (43.59 ± 0.96 kJ mol?1) and large negative values of ΔS1 (?116.98 ± 2.9 J K?1 mol?1) as well as ΔH2 (33.78 ± 0.51 kJ mol?1) and ΔS2 (?221.43 ± 1.57 J K?1 mol?1) indicate an associative mode of activation for both the aqua ligand substitution processes. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 252–259, 2003  相似文献   

10.
Cobalt Chelates for Hydrogenation Catalysts. II. Hydride Formation with [Co(dmgH)2] and [Co(dpnH)]+ In the presence of benzil as scavanger for the hydridocomplexes [Co(dpnH)]+ and [Co(dmgH)2] the hydride formation in water/n-propanol (50% v/v) becomes the rate determining step, and the ligand hydrogenation is completely suppressed in the case of [Co(dpnH)]+, but only partially in the case of [Co(dmgH)2]. The rate of hydride formation in both cases is 2nd order with respect to the complex, and the activation parameters ([Co(dmgH)2]: ΔH = 48.4 ± 1.0 kJ · mol–1, ΔS = ?57.4 ± 3.4J · mol?1 · K?1, [Co(dpnH)]+: ΔH = 52.7 = 0.4 kJ · mol?1, ΔS = ?59.8 ± 1.2J · mol?1 · K?1) indicate a H2-activation by homolytic splitting for both complexes. Some sources of error and possible causes for the missing activity of [Co(tim)]2+ are discussed.  相似文献   

11.
The thermal behavior and kinetic parameters of the exothermic decomposition reaction of N‐N‐bis[N‐(2,2,2‐tri‐nitroethyl)‐N‐nitro]ethylenediamine in a temperature‐programmed mode have been investigated by means of differential scanning calorimetry (DSC). The results show that kinetic model function in differential form, apparent activation energy Ea and pre‐exponential factor A of this reaction are 3(1 ‐α)2/3, 203.67 kJ·mol?1 and 1020.61s?1, respectively. The critical temperature of thermal explosion of the compound is 182.2 °C. The values of ΔS ΔH and ΔG of this reaction are 143.3 J·mol?1·K?1, 199.5 kJ·mol?1 and 135.5 kJ·mol?1, respectively.  相似文献   

12.
Cyclohexane and piperidine ring reversal in 1-(3-pentyloxyphenylcarbamoyloxy)-2-dialkylaminocyclohexanes was investigated by 13C NMR. An unusually low conformational energy ΔG = 0.59 kJ mol?1 and activation parameters ΔG218 = 43.8 ± 0.4 kJ mol?1, ΔH = 48.9 ± 2.5 kJ mol?1 and ΔS = 23 ± 9 J mol?1 K?1 were found for the diequatorial to diaxial transition of the cyclohexane ring in the trans-pyrrolidinyl derivative. In the trans-piperidinyl derivative, ΔG222 = 44.7 ± 0.5 KJ mol?1, ΔH = 55.7 ± 6.3 kJ mol?1 and ΔS = 51 ± 21 J mol?1 K?1 was found for the piperidine ring reversal from the non-equivalence of the α-carbons.  相似文献   

13.
The kinetics of the interaction of adenosine with cis‐[Pt(cis‐dach)(OH2)2]2+ (dach = diaminocyclohexane) was studied spectrophotometrically as a function of [cis‐[Pt(cis‐dach)(OH2)2]2+], [adenosine], and temperature at a particular pH (4.0), where the substrate complex exists predominantly as the diaqua species and the ligand adenosine exists as a neutral molecule. The substitution reaction shows two consecutive steps: the first is the ligand‐assisted anation followed by a chelation step. The activation parameters for both the steps have been evaluated using Eyring equation. The low negative value of ΔH1 (43.1 ± 1.3 kJ mol?1) and the large negative value of ΔS1 (?177 ± 4 J K?1 mol?1) along with ΔH2 (47.9 ± 1.8 kJ mol?1) and ΔS2 (?181 ± 6 J K?1 mol?1) indicate an associative mode of activation for both the aqua ligand substitution processes. The kinetic study was substantiated by infrared and electrospray ionization mass spectroscopic analysis. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 219–229, 2011  相似文献   

14.
Vanadium(II) ions form with the pyridine-2-carboxylate ligand a deep blue, tris-substituted complex absorbing at 660 nm (ε = 7.2 × 103 M?1) cm?1) with a shoulder at 450 nm. Reversible spectroelectrochemistry and cyclic voltammetry were observed for this complex, with E12 = ?0.448 V vs NHE, and ΔSrcθ = ?6 cal · mol?1 · deg?1. Electron transfer kinetics with [CO(en)3]3+ led to k12 = 3100 M?1 s?, ΔH = 12.4 kcal · mol?1 and ΔS = ?0.9 cal · mol?1 · deg?1 (I = 0.10 M). For the related [Co(NH3)6]3+ complex, k13 = 1.9 × 104 M?1 s?1. The self-exchange rate constant and activation parameters were analysed in terms of relative Marcus theory.  相似文献   

15.
Introduction 2,4,8,10-Tetranitro-2,4,8,10-tetraazaspiro[5,5]udecane- 3,9-dione is a typical cyclourea nitramine (Figure 1). Its crystal density is 1.91 gcm-3. The detonation velocity according to =1.90 gcm-3 is about 8670 ms-1. Its sensitivity to impact is better than that of cyclotrimethy- lenetrinitramine. So it is the potential high explosive. Its preparation,1-3 properties,1-3 hydrolytic behavior4 and electronic structure3 have been reported. In the present work, we report its kinetic pa…  相似文献   

16.
Restricted rotation about the naphthalenylcarbonyl bonds in the title compounds resulted in mixtures of cis and trans rotamers, the equilibrium and the rotational barriers depending on the substituents. For 2,7-dimethyl-1,8-di-(p-toluoyl)-naphthalene (1) ΔH° = 3.66 ± 0.14 kJ mol?1, ΔS° = 1.67 ± 0.63 J mol?1 K?1, ΔHct = 55.5 ± 1.3 kJ mol?1, ΔHct = 51.9 ± 1.3 kJ mol?1, ΔSct = ?41.3±4.1 J mol?1 K?1 and ΔSct = ?42.9±4.1 J mol?1 K?1. The rotation about the phenylcarbonyl bond requires ΔH = ?56.9±4.4 kJ mol?1 and ΔS = ?20.5±15.3 J mol?1 K?1 for the cis rotamer, and ΔH = 43.5Δ0.4 kJ mol?1 and ΔS =± ?22.4Δ1.3 J mol?1 K?1 for the trans rotamer. The role of electronic factors is likely to be virtually the same for both these rotamers but steric interaction between the two phenyl rings occurs in the cis rotamer only. Hence, the difference of the activation enthalpies obtained for the cis and trans rotamers, ΔΔH?1 = 13.4 kJ mol?1, provides a basis for the estimation of the role of steric factors in this rotation. For the tetracarboxylic acid 2 and its tetramethyl ester 3 the equilibrium is even more shifted towards the trans form because of enhanced steric and electrostatic interactions between the substituents in the cis form. The barriers for the rotation around the phenylcarbonyl bond and the cis-trans isomerization are lowered; an explanation for this result is presented.  相似文献   

17.
Introduction Dinitroglycoluril (DINGU) is a typical cyclourea nitramine. Its crystal density is 1.94 gcm-3. The detonation velocity corresponding to =1.94 gcm-3 is about 8450 ms-1. Its sensitivity to impact is better than that of cyclotrimethylenetrinitramine. It has the potential for possible use as high explosive from the point of view of the above-mentioned high performance. Its preparation,1-4 properties1-4 and hydrolytic behavior4 have been reported. In the present paper, we report i…  相似文献   

18.
邻苯二胺与5-氯-2-羟基二苯酮、邻香草醛作用合成了一种不对称希夫碱配体C27H21N2O3Cl(H2L)。在正丁醇和甲醇体系中硝酸铀酰与该配体反应合成了一种固体希夫碱配合物[UO2(HL)(NO3)(H2O)]·H2O。通过元素分析、IR、UV、1H NMR、TG-DTG及摩尔电导率分析等手段对合成的配合物进行了表征,用非等温热重法研究了铀(Ⅵ)配合物的热分解反应动力学,推断出第三步热分解的动力学方程为:d α /d t = A · e- E/RT ·3/2[(1- α )-1/3-1]-1,得到了动力学参数E和A。并计算出了活化熵△S¹和活化吉布斯自由能△G¹。  相似文献   

19.
The kinetics of the oxidation of ketorolac by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.75 mol·dm?3 was studied spectrophotometrically at 300 K. A plausible mechanism was proposed and the rate law was derived. The mechanism of oxidation of ketorolac (KET) in alkaline medium has been shown to proceed via a KET-HCF complex, which decomposes in a slow step followed by other fast steps to give the products. The main oxidative product was identified as (2,3-dihydro-1-hydroxy-1H-pyrrolizin-5-yl-)(phenyl)methanone and is characterized by its LC–ESI–MS spectrum. Thermodynamic parameters of various equilibria of the mechanism were calculated and activation parameters ΔH , ΔS , ΔG and log10 A were found to be 29.9 kJ·mol?1, ?220 J·K?1·mol?1, 96 kJ·mol?1 and 2.70 respectively.  相似文献   

20.
The ligand exchange MX5·L + *L?MX5·*L + L for the octahedral adducts MX5·L, in an inert solvent (CH2Cl2 or CHCl3) with neutral ligands, proceeds via a dissociative D mechanism when M = Nb, X = Cl and L = phosphoryl compound. A dissociative interchange Id mechanism is suggested when M = Nb or Ta, and X = F. A first order rate law and positive values for ΔS* (+4 to +14 cal K?1 mol?1) are observed for the exchanges on the pentachloride adducts. However, a second order rate law and large negative values for ΔS* (-15 to -24 cal K?1 mol?1) are found for the intermolecular neutral ligand exchange (measured by 1H-NMR.) and for the intramolecular fluorine exchange (measured by 19F-NMR.) reactions on the pentafluoride adducts. The fluorine exchange is 2 to 5 times faster than the ligand exchange. The exchanges, on the pentachloride and on the pentafluoride adducts, are slowed down with increasing donor strength of the phosphoryl compound.  相似文献   

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