The reaction of methyl radicals (Me) with hexafluoroacetone (HFA), generated from ditertiary butyl peroxide (dtBP), was studied over the temperature range of 402–433 K and the pressure range of 38–111 torr. The reaction resulted in the following displacement process taking place: where TFA refers to trifluoroacetone. The trifluoromethyl radicals that were generated abstract a hydrogen atom from the peroxide: such that k6a is given by: where θ = 2.303RT kcal/mol. The interaction of methyl and trifluoromethyl radicals results in the following steps: Product analysis shows that k17/kk = 2.0 ± 0.2 such that k17 = 1010.4±0.5M?1 · s?1. The rate constant k5 is given by: It is concluded that the preexponential factor for the addition of methyl radicals to ketones is lower than that for the addition of methyl radicals to olefins. 相似文献
We give necessary and sufficient conditions for sequences in the space AP(R) of continuous almost periodic functions on the
real line to converge in the weak topology. The abstract results are illustrated by a number of examples which show that weak
convergence seems to be a rare phenomenon. We also characterize the weakly compact subsets in AP(R). In particular, earlier
statements made in the monograph by Dunford and Schwartz are refined and completed. We close with some open problems. 相似文献
The near U-V photolysis of t-butyl nitrite has been studied over the temperature range 303–393 K. Under these conditions t-butyl nitrite was shown to be a very clean photochemical source of t-butoxy radicals. This allows a study of the decomposition of the t-butoxy radical to be made over this temperature range (3). (1) Extrapolation of the rate constants k3 to high pressure and combination with our previous thermal data give the results: 相似文献
Using dimethyl peroxide as a thermal source of methoxy radicals overthe temperature range of 110–160°C, and the combination of methoxy radicals and nitrogen dioxide as a reference reaction: a value was determined of the rate constant for the reaction of methoxy radicals with oxygen: is independent of nitrogen dioxide or oxygen concentration and added inert gas (carbon tetrafluoride). No heterogeneous effects were detected. The value of k4 is given by the expression In terms of atmospheric chemistry, this corresponds to a value of 105.6M?1·sec?1 at 298 K. Extrapolation to temperatures where the combustion of organic compounds has been studied (813 K) produces a value of 107.7M?1·sec?1 for k4. Under these conditions, reaction (4) competes with hydrogen abstraction or disproportionation reactions of the methoxy radical and its decomposition (3): In particular k3 is in the falloff region under these conditions. It is concluded that reaction (4) takes place as the result of a bimolecular collision process rather than via the formation of a cyclic complex. 相似文献
Conjugated tetraenes with both central double bonds of cis configuration undergo a series of thermal reactions, the observable products being markedly dependent on the nature of the terminal substituents. Dimethyl 2E,4Z,6Z,8E-decatetraene-1,10-dioate (16) was prepared and found to cyclize readily at 50° to trans dimethyl 2,4-bicyclo[4.2.0)octadiene-6,7-dicarboxylate (18). This reaction proceeds to equilibrium, and the rates and equilibrium constants at the indicated temperatures are: 3.0 × 10-5 sec-1 ?40°; 8.2 × 10-5 sec-1, 16.0,50°; ?10.0,75°; ?7.47,100° with the equilibrium favoring (18). A sample of 1,8-diphenyl-1E,3Z,5Z;7E-octatetraene (1) showed no reaction below 120°, and at 175° all trans 1,8-diphenyl-octatetraene, cis and trans stilbenes, trans-5-phenyl-6(cis-styryl)-1,3-cyclohexadiene cis-5-phenyl-6-(trans-styryl)-1,3-cyclohexadiene, and cis and trans 6,8-diphenyl-tricyclo[3.2.1.02.7]oct-3-enes were formed. At 100° in the presence of excess dimethyl acetylenedicarboxylate 1 gave dimethyl trans-3,4-diphenyltricyclo[4.2.2.02.5]deca-6,9-dien-6,7-dicarboxylate. Finally 1,4-di(1-cyclohexen-1-yl)-1,3-batadiyne, hydrogenated over a Lindlar catalyst, gave only tricyclo[10.4.0.06,11]hexadeca-1,3,5-triene. 相似文献
Most people in any community come into contact with chemicals that are potentially harmful to their health. Some elements are essential to health and inadequate amounts in food may also lead to ill health. Measurement of chemicals in blood, urine or other specimens is a fundamental feature of studies undertaken in the field of Occupational and Environmental Laboratory Medicine (OELM). Results are used to assess the risk for either overexposure or deficiency of essential nutrients. External Quality Assessment Schemes (EQAS) aid laboratories to achieve accurate and consistent data and 11 organisers of EQAS in Europe and North America are working to improve the effectiveness of their activities.The aims of the Network of EQAS Organisers in OELM are to stimulate improvements in analytical results, establish equivalence of assessment among Schemes, collaborate to enhance the practice of EQA including whenever possible to warrant traceability of EQAS to primary standards.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia. 相似文献
A Gaussian based model potential is used within FSGO formalism to study a series of two-valence-electron diatomics (Li2, Na2, K2, LiH, NaH, KH, MgH+, CaH+, LiNa, LiK and NaK) and triatomic ions (H2Li+, H2Na+, Li2Na+, Na2Li+, Li
3+
, Na
3+
, Li2H+ and Na2H+). Results for calculated equilibrium geometries, force constants, and energy changes for certain chemical reactions are compared to the corresponding quantities from available all-electronab initio studies and experimental results. The predicted results are generally satisfactory.Aided by grants to the University of North Carolina from the National Institute of Health and the National Science Foundation. 相似文献
The reaction of multi-bidentate oxamate-based copper(II) complexes with the [Ni(iPrtacn)Cl2] complex (iPrtacn:1,4,7-triisopropyl-1,4,7-triazacyclononane) has been investigated. X-ray diffraction studies reveal that for all compounds the oxamato κO,κΟ’ bidentate coordination site replaces the two chloride ions in [Ni(iPrtacn)Cl2] to form trimetallic {CuNi2} ( 1 – 3) , hexametallic {Cu2Ni4} ( 4 ) and enneametallic {Cu3Ni6} ( 5 ) complexes. The investigation of the magnetic properties shows that Cu−Ni interactions through the oxamato bridge are in the expected range (−111 cm−1, −68 cm−1). For 1 – 3 , both the sign and strength of the magnetic couplings are computed independently from DFT calculations, and these estimates broadly agree with the experiments. The magnetization measurements and EPR studies reveal that 1 – 3 are anisotropic: a significant portion of the large anisotropy of the [Ni(iPrtacn)Cl2] complex is retained, resulting in a D value for the S=3/2 ground state of 5 cm−1 on average. This is no longer the case for 4 and 5 where the anisotropy of the Ni(II) complexes is diluted due to the high nuclearity of the final edifices. These results show that it is possible to obtain trimetallic complexes with a high anisotropy and a high spin value for the ground state by a judicious choice of the interacting metal ions. 相似文献