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1.
The rate constants of the reactions of ethoxy (C2H5O), i‐propoxy (i‐C3H7O) and n‐propoxy (n‐C3H7O) radicals with O2 and NO have been measured as a function of temperature. Radicals have been generated by laser photolysis from the appropriate alkyl nitrite and have been detected by laser‐induced fluorescence. The following Arrhenius expressions have been determined: (R1) C2H5O + O2 → products k1 = (2.4 ± 0.9) × 10−14 exp(−2.7 ± 1.0 kJmol−1/RT) cm3 s−1 295K < T < 354K p = 100 Torr (R2) i‐C3H7O + O2 → products k2 = (1.6 ± 0.2) × 10−14 exp(−2.2 ± 0.2 kJmol−1/RT) cm3 s−1 288K < T < 364K p = 50–200 Torr (R3) n‐C3H7O + O2 → products k3 = (2.5 ± 0.5) × 10−14 exp(−2.0 ± 0.5 kJmol−1/RT) cm3 s−1 289K < T < 381K p = 30–100 Torr (R4) C2H5O + NO → products k4 = (2.0 ± 0.7) × 10−11 exp(0.6 ± 0.4 kJmol−1/RT) cm3 s−1 286K < T < 388K p = 30–500 Torr (R5) i‐C3H7O + NO → products k5 = (8.9 ± 0.2) × 10−12 exp(3.3 ± 0.5 kJmol−1/RT) cm3 s−1 286K < T < 389K p = 30–500 Torr (R6) n‐C3H7O + NO → products k6 = (1.2 ± 0.2) × 10−11 exp(2.9 ± 0.4 kJmol−1/RT) cm3s−1 289K < T < 380K p = 30–100 Torr All reactions have been found independent of total pressure between 30 and 500 Torr within the experimental error. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 860–866, 1999 相似文献
2.
Using the relative kinetic method, rate coefficients have been determined for the gas‐phase reactions of chlorine atoms with propane, n‐butane, and isobutane at total pressure of 100 Torr and the temperature range of 295–469 K. The Cl2 photolysis (λ = 420 nm) was used to generate Cl atoms in the presence of ethane as the reference compound. The experiments have been carried out using GC product analysis and the following rate constant expressions (in cm3 molecule?1 s?1) have been derived: (7.4 ± 0.2) × 10?11 exp [‐(70 ± 11)/ T], Cl + C3H8 → HCl + CH3CH2CH2; (5.1 ± 0.5) × 10?11 exp [(104 ± 32)/ T], Cl + C3H8 → HCl + CH3CHCH3; (7.3 ± 0.2) × 10?11 exp[?(68 ± 10)/ T], Cl + n‐C4H10 → HCl + CH3 CH2CH2CH2; (9.9 ± 2.2) × 10?11 exp[(106 ± 75)/ T], Cl + n‐C4H10 → HCl + CH3CH2CHCH3; (13.0 ± 1.8) × 10?11 exp[?(104 ± 50)/ T], Cl + i‐C4H10 → HCl + CH3CHCH3CH2; (2.9 ± 0.5) × 10?11 exp[(155 ± 58)/ T], Cl + i‐C4H10 → HCl + CH3CCH3CH3 (all error bars are ± 2σ precision). These studies provide a set of reaction rate constants allowing to determine the contribution of competing hydrogen abstractions from primary, secondary, or tertiary carbon atom in alkane molecule. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 651–658, 2002 相似文献
3.
New rate constant determinations for the reactions CH3 + HO2 → CH3O + OH (1) CH3 + HO2 → CH4 + O2 (2) CH3 + O2 → CH2O + OH (3) were made at 1000 K by fitting species profiles from high‐pressure flow reactor experiments on moist CO oxidation perturbed with methane. These reactions are important steps in the intermediate‐temperature burnout of hydrocarbon pollutants, especially at super‐atmospheric pressure. The experiments used in the fit were selected to minimize the uncertainty in the determinations. These uncertainties were estimated using model sensitivity coefficients, derived for time‐shifted flow reactor experiments, along with literature uncertainties for the unfitted rate constants. The experimental optimization procedure significantly reduced the uncertainties in each of these rate constants over the current literature values. The new rate constants and their uncertainties were determined to be, at 1000 K: k1 = 1.48(10)13 cm3 mol−1 s−1 (UF = 2.24) k2 = 3.16(10)12 cm3 mol−1 s−1 (UF = 2.89) k3 = 2.36(10)8 cm3 mol−1 s−1 (UF = 4.23) There are no direct and few indirect measurements of reactions ( 1 ) and ( 2 ) in the literature. There are few measurements of reaction ( 3 ) near 1000 K. These results therefore represent an important refinement to radical oxidation chemistry of significance to methane and higher alkane oxidation. The model sensitivity analysis used in the experimental design was also used to characterize the mechanistic dependence of the new rate constant values. Linear sensitivities of the fitted rate constants to the unfitted rate constants were given. The sensitivity analysis was used to show that the determinations above are primarily dependent on the rate constants chosen for the reactions CH3 + CH3 + M → C2H6 + M and CH2O + HO2 → HCO + H2O2. Uncertainties in the rate constants of these two reactions are the primary contributors to the uncertainty factors given above. Further reductions in the uncertainties of these kinetics would lead to significant reductions in the uncertainties in our determinations of k1, k2, and k3. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 75–100, 2001 相似文献
4.
Nick M. Marinov 《国际化学动力学杂志》1999,31(3):183-220
A detailed chemical kinetic model for ethanol oxidation has been developed and validated against a variety of experimental data sets. Laminar flame speed data (obtained from a constant volume bomb and counterflow twin‐flame), ignition delay data behind a reflected shock wave, and ethanol oxidation product profiles from a jet‐stirred and turbulent flow reactor were used in this computational study. Good agreement was found in modeling of the data sets obtained from the five different experimental systems. The computational results show that high temperature ethanol oxidation exhibits strong sensitivity to the fall‐off kinetics of ethanol decomposition, branching ratio selection for C2H5OH + OH ↔ Products, and reactions involving the hydroperoxyl (HO2) radical. The multichanneled ethanol decomposition process is analyzed by RRKM/Master Equation theory, and the results are compared with those obtained from earlier studies. The ten‐parameter Troe form is used to define the C2H5OH(+M) ↔ CH3 + CH2OH(+M) rate expression as k∞ = 5.94E23 T−1.68 exp(−45880 K/T) (s−1) ko = 2.88E85 T−18.9 exp(−55317 K/T) (cm3/mol/sec) Fcent = 0.5 exp(−T/200 K) + 0.5 exp(−T/890 K) + exp(−4600 K/T) and the C2H5OH(+M) ↔ C2H4 + H2O(+M) rate expression as k∞ = 2.79E13 T0.09 exp(−33284 K/T) (s−1) ko = 2.57E83 T−18.85 exp(−43509 K/T) (cm3/mol/sec) F cent = 0.3 exp(−T/350 K) + 0.7 exp(−T/800 K) + exp(−3800 K/T) with an applied energy transfer per collision value of <ΔEdown> = 500 cm−1. An empirical branching ratio estimation procedure is presented which determines the temperature dependent branching ratios of the three distinct sites of hydrogen abstraction from ethanol. The calculated branching ratios for C2H5OH + OH, C2H5OH + O, C2H5OH + H, and C2H5OH + CH3 are compared to experimental data. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 183–220, 1999 相似文献
5.
The reaction of acetylferrocene [Fe(η‐C5H5)(η‐C5H4COCH3)] (1) with (2‐isopropyl‐5‐methylphenoxy) acetic acid hydrazide [CH3C6H3CH(CH3)2OCH2CONHNH2] (2) in refluxing ethanol gives the stable light‐orange–brown Schiff base 1‐[(2‐isopropyl‐5‐methylphenoxy)hydrazono] ethyl ferrocene, [CH3C6H3CH(CH3)2OCH2CONHN?C(CH3)Fe(η‐C5H5)(η‐C5H4)] (3). Complex 3 has been characterized by elemental analysis, IR, 1H NMR and single crystal X‐ray diffraction study. It crystallizes in the monoclinic space group P21/n, with a = 9.6965(15), b = 7.4991(12), c = 29.698(7) Å, β = 99.010(13) °, V = 2132.8(7) Å3, Dcalc = 1.346 Mg m?3; absorption coefficient, 0.729 mm?1. The crystal structure clearly shows the characteristic [N? H···O] hydrogen bonding between the two adjacent molecules of 3. This acts as a bidentale ligand, which, on treatment with [Ru(CO)2Cl2] n, gives a stable bimetallic yellow–orange complex (4). Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
6.
Reijo Sillanp Jordi Llop Clara Vias Francecs Teixidor Raikko Kiveks 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(8):900-901
In the title compound, (η5‐2,5‐dimethylpyrrolyl)[(7,8,9,10,11‐η)‐7‐methyl‐7,8‐dicarba‐nido‐undecaborato]cobalt(III), [3‐Co{η5‐[2,5‐(CH3)2‐NC4H2]}‐1‐CH3‐1,2‐C2B9H10] or [Co(C3H13B9)(C6H8N)], the CoIII atom is sandwiched between the pentagonal faces of the pyrrolyl and dicarbollide ligands, resulting in a neutral molecule. The C—C distance in the dicarbollide cage is 1.649 (3) Å. 相似文献
7.
The kinetics of C6H5 reactions with n‐CnH2n+2 (n = 3, 4, 6, 8) have been studied by the pulsed laser photolysis/mass spectrometric method using C6H5COCH3 as the phenyl precursor at temperatures between 494 and 1051 K. The rate constants were determined by kinetic modeling of the absolute yields of C6H6 at each temperature. Another major product C6H5CH3 formed by the recombination of C6H5 and CH3 could also be quantitatively modeled using the known rate constant for the reaction. A weighted least‐squares analysis of the four sets of data gave k (C3H8) = (1.96 ± 0.15) × 1011 exp[?(1938 ± 56)/T], and k (n‐C4H10) = (2.65 ± 0.23) × 1011 exp[?(1950 ± 55)/T] k (n‐C6H14) = (4.56 ± 0.21) × 1011 exp[?(1735 ± 55)/T], and k (n?C8H18) = (4.31 ± 0.39) × 1011 exp[?(1415 ± 65)T] cm3 mol?1 s?1 for the temperature range studied. For the butane and hexane reactions, we have also applied the CRDS technique to extend our temperature range down to 297 K; the results obtained by the decay of C6H5 with CRDS agree fully with those determined by absolute product yield measurements with PLP/MS. Weighted least‐squares analyses of these two sets of data gave rise to k (n?C4H10) = (2.70 ± 0.15) × 1011 exp[?(1880 ± 127)/T] and k (n?C6H14) = (4.81 ± 0.30) × 1011 exp[?(1780 ± 133)/T] cm3 mol?1 s?1 for the temperature range 297‐‐1046 K. From the absolute rate constants for the two larger molecular reactions (C6H5 + n‐C6H14 and n‐C8H18), we derived the rate constant for H‐abstraction from a secondary C? H bond, ks?CH = (4.19 ± 0.24) × 1010 exp[?(1770 ± 48)/T] cm3 mol?1 s?1. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 49–56, 2004 相似文献
8.
Mark Bartholomä Dr. Sergej Gisbrecht Dipl.‐Chem. Stefan Stucky Dr. Christian Neis Dr. Bernd Morgenstern Dr. Kaspar Hegetschweiler Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(11):3326-3340
The hexadentate ligand all‐cis‐N1,N2‐bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine (Le) was synthesized in five steps with an overall yield of 39 % by using [Ni(taci)2]SO4?4 H2O as starting material (taci=1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol). Crystal structures of [Na0.5(H6Le)](BiCl6)2Cl0.5?4 H2O ( 1 ), [Ni(Le)]‐ Cl2?5 H2O ( 2 ), [Cu(Le)](ClO4)2?H2O ( 3 ), [Zn(Le)]CO3?7 H2O ( 4 ), [Co(Le)](ClO4)3 ( 5 c ), and [Ga(H?2Le)]‐ NO3?2 H2O ( 6 ) are reported. The Na complex 1 exhibited a chain structure with the Na+ cations bonded to three hydroxy groups of one taci subunit of the fully protonated H6(Le)6+ ligand. In 2 , 3 , 4 , and 5 c , a mononuclear hexaamine coordination was found. In the Ga complex 6 , a mononuclear hexadentate coordination was also observed, but the metal binding occurred through four amino groups and two alkoxo groups of the doubly deprotonated H?2(Le)2?. The steric strain within the molecular framework of various M(Le) isomers was analyzed by means of molecular mechanics calculations. The formation of complexes of Le with MnII, CuII, ZnII, and CdII was investigated in aqueous solution by using potentiometric and spectrophotometric titration experiments. Extended equilibrium systems comprising a large number of species were observed, such as [M(Le)]2+, protonated complexes [MHz(Le)]2+z and oligonuclear aggregates. The pKa values of H6(Le)6+ (25 °C, μ=0.10 m ) were found to be 2.99, 5.63, 6.72, 7.38, 8.37, and 9.07, and the determined formation constants (log β) of [M(Le)]2+ were 6.13(3) (MnII), 20.11(2) (CuII), 13.60(2) (ZnII), and 10.43(2) (CdII). The redox potentials (vs. NHE) of the [M(Le)]3+/2+ couples were elucidated for Co (?0.38 V) and Ni (+0.90 V) by cyclic voltammetry. 相似文献
9.
A laser flash photolysis–resonance fluorescence technique has been employed to study the kinetics of the reactions of atomic chlorine with acetone (CH3C(O)CH3; k1), 2‐butanone (C2H5C(O)CH3; k2), and 3‐pentanone (C2H5C(O)C2H5; k3) as a function of temperature (210–440 K) and pressure (30–300 Torr N2). No significant pressure dependence is observed for any of the reactions studied. Arrhenius expressions (units are 10?11 cm3 molecule?1 s?1) obtained from the data are k1(T) = (1.53 ± 0.19) exp[(?594 ± 33)/T], k2(T) = (2.77 ± 0.33) exp[(+76 ± 33)/T], and k3(T) = (5.66 ± 0.41) exp[(+87 ± 22)/T], where uncertainties are 2σ and represent precision only. The accuracy of reported rate coefficients is estimated to be ±15% over the entire range of pressure and temperature investigated. The room temperature rate coefficients reported in this study are in good agreement with a majority of literature values. However, the activation energies reported in this study are in poor agreement with the literature values, particularly for 2‐butanone and 3‐pentanone. Possible explanations for discrepancies in published kinetic parameters are proposed, and the potential role of Cl + ketone reactions in atmospheric chemistry is discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 259–267, 2008 相似文献
10.
Olga Crespo M. Concepcin Gimeno Peter G. Jones Antonio Laguna 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(1):46-47
The title compound, 7‐[(Ph2P)Au(PPh3)]‐8‐(CH3)‐7,8‐nido‐C2B9H10]·0.5CH2Cl2 or [Au(C15H23B9P)(C18H15P)]·0.5CH2Cl2, is the first reported gold derivative of the ligand [7‐(Ph2P)‐8‐(CH3)‐7,8‐nido‐C2B9H10]?. It has a mononuclear structure with the gold centre in an essentially linear coordination [P—Au—P 174.041 (15)°]. The open C2B3 face contains one H atom that is strongly bonded to the central B atom and semi‐bridging to a neighbouring B atom [B—H distances 1.070 (16) and 1.45 (3) Å]. 相似文献
11.
Two new three‐dimensional frameworks with zeolite‐like channels were prepared in the presence of 1,6‐diaminohexane. Cu1.5(H3N–(CH2)6–NH3)0.5[C6H2(COO)4] · 5H2O ( 1 ) crystallizes in the triclinic space group P$\bar{1}$ with a = 772.56(7), b = 1110.36(7), c = 1111.98(8) pm, α = 98.720(7)°, β = 108.246(9)°, and γ = 95.559(7)°. Cu2(H3N–(CH2)6–NH3)0.5(OH)[C6H2(COO)4] · 3H2O ( 2 ) crystallizes in the monoclinic space group P2/c with a = 1159.34(11), b = 1059.44(7), c = 1582.2(2) pm, and β = 106.130(11)°. The Cu2+ coordination polyhedra are connected by [C6H2(COO)4]4– anions to yield three‐dimensional frameworks with wide centrosymmetric channel‐like voids. Complex 1 reveals voids extending along [100] with diagonals of 900 pm and 300 pm, whereas in complex 2 the diagonal of the nearly rectangular crossection of the channels extending parallel to [001] is 900 pm. The negative excess charges of the frameworks are compensated by [H3N–(CH2)6–NH3]2+ cations, which occupy the voids along with water molecules. The [H3N–(CH2)6–NH3]2+ cations are not connected to Cu2+ and have served as templates. 相似文献
12.
A class of extended 2,5‐disubstituted‐1,3,4‐oxadiazoles R1‐C6H4‐{OC2N2}‐C6H4‐R2 (R1=R2=C10H21O 1 a , p‐C10H21O‐C6H4‐C?C 3 a , p‐CH3O‐C6H4‐C?C 3 b ; R1=C10H21O, R2=CH3O 1 b , (CH3)2N 1 c ; F 1 d ; R1=C10H21O‐C6H4‐C?C, R2=C10H21O 2 a , CH3O 2 b , (CH3)2N 2 c , F 2 d ) were prepared, and their liquid‐crystalline properties were examined. In CH2Cl2 solution, these compounds displayed a room‐temperature emission with λmax at 340–471 nm and quantum yields of 0.73–0.97. Compounds 1 d , 2 a – 2 d , and 3 a exhibited various thermotropic mesophases (monotropic, enantiotropic nematic/smectic), which were examined by polarized‐light optical microscopy and differential scanning calorimetry. Structure determination by a direct‐space approach using simulated annealing or parallel tempering of the powder X‐ray diffraction data revealed distinctive crystal‐packing arrangements for mesogenic molecules 2 b and 3 a , leading to different nematic mesophase behavior, with 2 b being monotropic and 3 a enantiotropic in the narrow temperature range of 200–210 °C. The structural transitions associated with these crystalline solids and their mesophases were studied by variable‐temperature X‐ray diffractometry. Nondestructive phase transitions (crystal‐to‐crystal, crystal‐to‐mesophase, mesophase‐to‐liquid) were observed in the diffractograms of 1 b, 1 d , 2 b, 2 d , and 3 a measured at 25–200 °C. Powder X‐ray diffraction and small‐angle X‐ray scattering data revealed that the structure of the annealed solid residue 2 b reverted to its original crystal/molecular packing when the isotropic liquid was cooled to room temperature. Structure–property relationships within these mesomorphic solids are discussed in the context of their molecular structures and intermolecular interactions. 相似文献
13.
The ability to use calculated OH frequencies to assign experimentally observed peaks in hydrogen bonded systems hinges on the accuracy of the calculation. Here we test the ability of several commonly employed model chemistries—HF, MP2, and several density functionals paired with the 6‐31+G(d) and 6‐311++G(d,p) basis sets—to calculate the interaction energy (De) and shift in OH stretch fundamental frequency on dimerization (δ(ν)) for the H2O → H2O, CH3OH → H2O, and H2O → CH3OH dimers (where for X → Y, X is the hydrogen bond donor and Y the acceptor). We quantify the error in De and δ(ν) by comparison to experiment and high level calculation and, using a simple model, evaluate how error in De propagates to δ(ν). We find that B3LYP and MPWB1K perform best of the density functional methods studied, that their accuracy in calculating δ(ν) is ≈ 30–50 cm?1 and that correcting for error in De does little to heighten agreement between the calculated and experimental δ(ν). Accuracy of calculated δ(ν) is also shown to vary as a function of hydrogen bond donor: while the PBE and TPSS functionals perform best in the calculation of δ(ν) for the CH3OH → H2O dimer their performance is relatively poor in describing H2O → H2O and H2O → CH3OH. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
14.
Dorcas M. M. Farrell George Ferguson Alan J. Lough Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):o6-o8
In the hydrated adduct N,N′‐dimethylpiperazine‐1,4‐diium bis(3‐carboxy‐2,3‐dihydroxypropanoate) dihydrate, [MeNH(CH2CH2)2NHMe]2+·2(C4H5O6)?·2H2O or C6H16N22+·2C4H5O6?·2H2O, formed between racemic tartaric acid and N,N′‐dimethylpiperazine (triclinic P, Z′ = 0.5), the cations lie across centres of inversion. The anions alone form chains, and anions and water molecules together form sheets; the sheets are linked by the cations to form a pillared‐layer framework. The supramolecular architecture thus takes the form of a family of N‐dimensional N‐component structures having N = 1, 2 or 3. 相似文献
15.
A laser photolysis–long path laser absorption (LP‐LPLA) experiment has been used to determine the rate constants for H‐atom abstraction reactions of the dichloride radical anion (Cl2−) in aqueous solution. From direct measurements of the decay of Cl2− in the presence of different reactants at pH = 4 and I = 0.1 M the following rate constants at T = 298 K were derived: methanol, (5.1 ± 0.3)·104 M−1 s−1; ethanol, (1.2 ± 0.2)·105 M−1 s−1; 1‐propanol, (1.01 ± 0.07)·105 M−1 s−1; 2‐propanol, (1.9 ± 0.3)·105 M−1 s−1; tert.‐butanol, (2.6 ± 0.5)·104 M−1 s−1; formaldehyde, (3.6 ± 0.5)·104 M−1 s−1; diethylether, (4.0 ± 0.2)·105 M−1 s−1; methyl‐tert.‐butylether, (7 ± 1)·104 M−1 s−1; tetrahydrofuran, (4.8 ± 0.6)·105 M−1 s−1; acetone, (1.41 ± 0.09)·103 M−1 s−1. For the reactions of Cl2− with formic acid and acetic acid rate constants of (8.0 ± 1.4)·104 M−1 s−1 (pH = 0, I = 1.1 M and T = 298 K) and (1.5 ± 0.8) · 103 M−1 s−1 (pH = 0.42, I = 0.48 M and T = 298 K), respectively, were derived. A correlation between the rate constants at T = 298 K for all oxygenated hydrocarbons and the bond dissociation energy (BDE) of the weakest C‐H‐bond of log k2nd = (32.9 ± 8.9) − (0.073 ± 0.022)·BDE/kJ mol−1 is derived. From temperature‐dependent measurements the following Arrhenius expressions were derived: k (Cl2− + HCOOH) = (2.00 ± 0.05)·1010·exp(−(4500 ± 200) K/T) M−1 s−1, Ea = (37 ± 2) kJ mol−1 k (Cl2− + CH3COOH) = (2.7 ± 0.5)·1010·exp(−(4900 ± 1300) K/T) M−1 s−1, Ea = (41 ± 11) kJ mol−1 k (Cl2− + CH3OH) = (5.1 ± 0.9)·1012·exp(−(5500 ± 1500) K/T) M−1 s−1, Ea = (46 ± 13) kJ mol−1 k (Cl2− + CH2(OH)2) = (7.9 ± 0.7)·1010·exp(−(4400 ± 700) K/T) M−1 s−1, Ea = (36 ± 5) kJ mol−1 Finally, in measurements at different ionic strengths (I) a decrease of the rate constant with increasing I has been observed in the reactions of Cl2− with methanol and hydrated formaldehyde. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 169–181, 1999 相似文献
16.
Werner Complexes with ω‐Dimethylaminoalkyl Substituted Ethylenediamine Ligands: Bifunctional Hydrogen‐Bond‐Donor Catalysts for Highly Enantioselective Michael Additions
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M. Sc. Subrata K. Ghosh Dr. Carola Ganzmann Dr. Nattamai Bhuvanesh Prof. Dr. John A. Gladysz 《Angewandte Chemie (International ed. in English)》2016,55(13):4356-4360
The racemic carbonate complex [Co(en)2O2CO]+ Cl? (en=1,2‐ethylenediamine) and (S)‐[H3NCH((CH2)nNHMe2)CH2NH3]3+ 3 Cl? (n=1–4) react (water, charcoal, 100 °C) to give [Co(en)2((S)‐H2NCH((CH2)nNHMe2)CH2NH2)]4+ 4 Cl? ( 3 a – d H4+ 4 Cl?) as a mixture of Λ/Δ diastereomers that separate on chiral‐phase Sephadex columns. These are treated with NaOH/Na+ BArf? (BArf=B(3,5‐C6H3(CF3)2)4) to give lipophilic Λ‐ and Δ‐ 3 a–d 3+ 3 BArf?, which are screened as catalysts (10 mol %) for additions of dialkyl malonates to nitroalkenes. Optimal results are obtained with Λ‐ 3 c 3+ 3 BArf? (CH2Cl2, ?35 °C; 98–82 % yields and 99–93 % ee for six β‐arylnitroethenes). The monofunctional catalysts Λ‐ and Δ‐[Co(en)3]3+ 3 BArf? give enantioselectivities of <10 % ee with equal loadings of Et3N. The crystal structure of Δ‐ 3 a H4+ 4 Cl? provides a starting point for speculation regarding transition‐state assemblies. 相似文献
17.
Khalil A. Abboud Peter N. Nickias Eugene Y.‐X. Chen 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):m41-m42
In the structure of bis({N‐[dimethyl(1η5‐2,3,4,6‐tetramethylindenyl)silyl]cyclohexylamido‐1κN}(methyl‐3κC)‐di‐μ3‐methylene‐1:2:3κ3C;1:3:3′κ3C‐tris(pentafluorophenyl‐2κC)titanium) benzene disolvate, [Me2Si(η5‐2,3,4,6‐Me4C9H2)(C6H11N)]Ti[(μ3‐CH2)Al(C6F5)3][AlMe(μ3‐CH2)]2 or [Ti2(C21H7AlF15)2(C21H31NSi)2]·2C6D6, the dimer is located on an inversion center, and the two Ti centers are linked by double Ti(μ3‐CH2)Al(C6F5)3AlMe(μ3‐CH2) heterocycles. The electron‐deficient Ti centers are further stabilized by two α‐agostic interactions between Ti and one H atom of each bridging methylene group. 相似文献
18.
The gas phase photodissociation spectra of four protonated β-diketones were obtained and compared with the absorption spectra of the corresponding ions in solution. Protonated 2,4-pentanedione was observed to undergo the photodissociation process [C5H9O2]+ +hν → [CH3CO]+ +C3H6O with a λmax at 276±10 nm compared with a solution absorption maximum at 286 nm. Protonated 2,4-hexanedione was observed to undergo the photodissociation processes [C6H11O2]+ +hν → [CH3CO]+ +C4H8O and [C6H11O2]+ +hν → [C2H5CO]+ +C3H6O with a λmax at 279±10 nm compared with a solution absorption maximum at 288 nm. Protonated 3-methyl-2,4-pentanedione was observed to undergo the photodissociation process [C6H11O2]+ +hν → [CH3CO]+ +C4H8O with a λmax at 295±10 nm compared with a solution absorption maximum at 305 nm. Protonated 1,1,1-trifluoro-2,4-pentanedione was observed to undergo the photodissociation process [C5H6F3O2]+ +hν → CF3H+[C4H5O2]+ with a λmax at 273±10 nm compared with a solution absorption maximum at 288 nm. The [CH3CO]+ and [C2H5CO]+ produced photochemically with the first three ions react to regenerate the protonated β-diketone leading to a photostationary state. Photodissociation of the protonated alkyl β-diketones is believed to occur from the protonated keto form, whereas photodissociation of protonated 1,1,1-trifluoro-2,4-pentanedione is believed to occur from the protonated enol form. Mechanisms for the observed photodissociation processes are proposed and comparisons with results from related techniques are presented. 相似文献
19.
The crystal structure of [(p‐CH3C6H4)3GeCH(o‐CH3C6H4)CH2CO2]2Sn(C4H9)2 consists of a monomer with the atoms of tin and germanium both occupying tetrahedral geometries. However, the tin atom is distorted towards a skew trapezoidal bipyramid geometry as a result of weakly chelating carboxylate ligands. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
20.
Johan K. Terlouw Wigger Heerma John L. Holmes Peter C. Burgers 《Journal of mass spectrometry : JMS》1980,15(11):582-586
The [C4H6O]+˙ ion of structure [CH2?CHCH?CHOH]+˙ (a) is generated by loss of C4H8 from ionized 6,6-dimethyl-2-cyclohexen-1-ol. The heat of formation ΔHf of [CH2?CHCH?CHOH]+˙ was estimated to be 736 kJ mol?1. The isomeric ion [CH2?C(OH)CH?CH2]+˙ (b) was shown to have ΔHf, ? 761 kJ mol?1, 54 kJ mol?1 less than that of its keto analogue [CH3COCH?CH2]+˙. Ion [CH2?C(OH)CH?CH2]+˙ may be generated by loss of C2H4 from ionized hex-1-en-3-one or by loss of C4H8 from ionized 4,4-dimethyl-2-cyclohexen-1-ol. The [C4H6O]+˙ ion generated by loss of C2H4 from ionized 2-cyclohexen-1-ol was shown to consist of a mixture of the above enol ions by comparing the metastable ion and collisional activation mass spectra of [CH2?CHCH?CHOH]+˙ and [CH2?C(OH)CH?CH2]+˙ ions with that of the above daughter ion. It is further concluded that prior to their major fragmentations by loss of CH3˙ and CO, [CH2?CHCH?CHOH]+˙ and [CH2?C(OH)CH?CH2]+˙ do not rearrange to their keto counterparts. The metastable ion and collisional activation characteristics of the isomeric allenic [C4H6O]+˙ ion [CH2?C?CHCH2OH]+˙ are also reported. 相似文献