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1.
Numerous experimental data for the cyclization of free radicals C·H2(CH2)nCH=CH2 cyclo-[(CH2)n+1CH(C·H2)], and C·H2(CH2)nCH=CHR cyclo-[(CH2)n+1C·HCHR] were analyzed in the framework of the parabolic model. The activation energy of thermoneutral (H e = 0) cyclization E e0 decreases linearly with an increase in the energy of cycle strain E rsc: E e0(n) (kJ mol–1) = 85.5 – 0.44E rsc(n) (n is the number of atoms in the cycle). The activation entropy of cyclization S # also depends on the cycle size: the larger the cycle, the lower S #. A linear dependence of S # on the difference between the entropies of formation S° of cyclic hydrocarbon and the corresponding paraffin was found: S # = 1.00[S°(cycle) – S°(CnH2n+2)]. The E e0 values coincide for cyclization reactions with the formation of the six-membered cycle and the bimolecular addition of alkyl radicals to olefins.  相似文献   

2.
The parabolic model of radical abstraction reactions is used to analyze experimental data on monomolecular hydrogen-atom transfer in the reactionsRC.H(CH2) n CH2R1 RCH2(CH2) n C.HR1(n= 2, 3, 4)RCH(O.)(CH2)2CH2R1 RCH(OH)(CH2)2C.HR1 RCH(OO.)(CH2) n CH2R1 RCH(OOH)(CH2) n C.HR1(n= 1, 2).The activation energies and rate constants that specify each class of these reactions are calculated. Alkyl radical isomerization is characterized by the following activation energies of a thermally neutral reaction depending on the cycle size in the transition state (nis the number of atoms in a cycle): E e , 0(kJ/mol) = 46.6 (n= 6), 59.4 (n= 5), and 57.1 (n= 7). Alkoxy radicals isomerize with E e , 0(kJ/mol) = 53.4 (n= 6), whereas peroxy radicals isomerize with E e , 0(kJ/mol) = 53.2 (n= 6) and E e , 0(kJ/mol) = 54.8 (n= 7). The E e , 0value varies with changes in the cycle size and the strain energy in cycloparaffin C n H2n in the same manner. The activation energies E e , 0for the intra- and intermolecular H-atom abstractions are compared. It is found that E e , 0(isomerization) < E e , 0(R.+ R1H) for alkyl radicals and that E e , 0(isomerization) E e , 0(RO.(RO.) + R1H) for alkoxy and peroxy radicals.  相似文献   

3.
The process of chain termination in the oxidation of cumene was studied. With the use of the semiempirical PM3 method, the structures of primary and tertiary peroxide radicals (PhCH(CH3)CH2OO· and Ph(CH3)2COO·), the PhCH(CH3)CH2OOOOC(CH3)2Ph tetroxide (TO) (the product of the combination of the above radicals), and TO decomposition products were studied and their heats of formation (H 0 f) were determined; the activation energy of TO decomposition was evaluated. Similar values of H 0 f were obtained by the thermochemical method of group additivity. The PM3 calculation demonstrated that the irreversible decomposition of the asymmetric TO in a six-membered transition complex into the PhCH(CH3)CHO aldehyde, the Ph(CH3)COH alcohol, and O2 is a synchronous process: dramatic changes in the bond lengths and bond orders occurred simultaneously. In this case, 100 kcal/mol was released, which is sufficient for the chemiexcitation of triplet R–H=O and singlet O2. A conclusion was drawn that a small impurity of PhCH(CH3)CH2OO· primary radicals plays an important role in chain termination and is the only reason for the excitation of chemiluminescence.  相似文献   

4.
The intersecting parabolas model is used to analyze experimental data for the following radical cyclization and decyclization reactions: RCH=CH(CH2)nN·R1 cyclo-[NR1CH(CH2)n]C·HR,R(CH2)2OOCH2C·HR cyclo-[RCHOCH2] + RCH2CH2O·, cyclo-[(CH2)nOOCHC· HR] cyclo-[RCHOCH](CH2)nO·, cyclo-[(CH2)nOC·RO] RC(O)O(CH2) n–1C·H2, and cyclo-[(CH2)nCHO·] CH(O)(CH2) n–1C·H2. The activation energy of the thermally neutral reaction (E e,0) is calculated for each class of reactions. E e,0 depends on the electronegativity of the heteroatom Y of the reaction center C C...Y, the force constants of the reacting bonds, and the strain energy of the ring formed. For the cyclization and decyclization of six-membered rings, the empirical relationship between the elongation of the reacting bonds in the transition state (r e) and the difference in electronegativity (EA) between the C and Y atoms (Y = C, N, O) has the form r e ×1011, m = 3.83 – 0.0198(EA, kJ/mol).Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 5–13.Original Russian Text Copyright © 2005 by Denisova, Denisov.  相似文献   

5.
A parabolic model of bimolecular radical reactions was used for analysis of the hydrogen transfer reactions of ketyl radicals: >C·OH+R1COR2→>C=O+R1R2C·OH. The parameters describing the reactivity of the reagents were calculated from the experimental data. The parameters that characterize the reactions of ketyl and alkyl radicals as hydrogen donors with olefins and with carbonyl compounds were obtained: >C·OH+R1CH=CH2→>C=O+R1C·HCH3; >R1CH=CH2+R2C·HCH2R3→R2C·HCH3+R2CH=CHR3. These parameters were used to calculate the activation energies of these transformations. The kinetic parameters of reactions of hydrogen abstraction by free radicals and molecules (adelhydes, ketones, and quinones) from the C−H and O−H bonds were compared. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2178–2184, November, 1998.  相似文献   

6.
The 4,4′-bis(RfCH2OCH2)-2,2′-bpy ligands [Rf = n-C3F7 (1a), HCF2(CF2)3 (1b)] were prepared and then treated with [MCl2(CH3CN)2] (M = Pt or Pd) to result in the corresponding metal complexes, [MCl2(4,4′-bis(RfCH2OCH2)-2,2′-bpy)] (M = Pt 2a–b; Pd 3a–b). Both ligands and metal complexes were fully characterized by multi-nuclei NMR (1H, 19F and 13C), FTIR, and mass (GC/MS or HR-FAB) methods. The X-ray structures of 2a–b and 3a–b were studied. With terminal CF3, the structures of 2a and 3a exhibit disordered polyfluorinated regions in solid state. With terminal HCF2, the structures of 2b and 3b show a π–π stacking of the bpy planes, five-membered C–H···O hydrogen bond and an unusual intramolecular blue-shifting C–H···F–C hydrogen bond system, whereas without terminal HCF2, the structures of 2a and 3a show the similar π–π stacking, five-membered C–H···O hydrogen bond and typical orientation of polyfluorinated ponytails, but not the C–H···F–C hydrogen bond system. The CV and UV/Vis studies were also carried out.  相似文献   

7.
Using EPR spectroscopy, the rate constants for the addition of radicals CC13(CH2· CH2)n, (R1 for n=1 and R2 for n=2), CCl3CH2CHCH3 (R3), and CCl3CH2CHCl (R4) to unsaturated compounds CH2=CHX (X=C6H5, COOCH3, CN) and CH2=C(CH3)Y (Y=C6H5, COOCH3) at 22C have been determined. The radicals R1 and R2 exhibit ambiphilic, and R4 electrophilic character towards the selected unsaturated compounds. It has been shown that the presence of the CCl3 group in the -position of the radical center has little effect on the reactivity of the radical. Replacement of a hydrogen on the -carbon in radical R1 by a CH3 group or chlorine atom leads to a considerable reduction in the rate of addition of the radicals to the unsaturated compounds examined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 548–554, March, 1991.  相似文献   

8.
1.  The competitive kinetics method was used to show that hydrogen abstraction from propylene by telomeric CCl3[CH2CH(CH3)]n radicals (n=1, 2) proceeds at 140°C with rate constants 2.5·103 and 1.8·103 liters/mole·sec, respectively.
2.  The polar effect upon the abstraction of hydrogen atoms from propylene by telomer radicals is less pronounced than upon the abstraction of a chlorine atom from CCl4.
Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 894–897, April, 1988.  相似文献   

9.
Photochemical transformations of phenothiazine (PTA) in solutions of halomethanes CHnX4–n (X = Cl, Br; n = 0, 1, 2) and in n-hexane—CHnX4–n mixtures under the irradiation with = 337 and 365 nm were studied. The rate constants of quenching of PTA fluorescence with halomethanes (k q) are 4·105—1.3·1010 L mol–1 s–1. The process occurs due to electron transfer with the C—X bond cleavage in the radical anion fragment of the primary radical ion pair. This results in the formation of the stable radical cation salt (PTA·+X). The plot of k q vs. free energy of electron transfer corresponds to the Rehm—Weller empirical equation for a one-electron process and is satisfactorily described in terms of the theory of nonradiative electron transitions in the approximation of one quantum vibration.  相似文献   

10.
The rate constants of hydrogen splitting from hydrogen donors (DH) by the ClCH2(CH2)3CCl2 radicals (R1) were determined by the method of competitive kinetics in the temperature range of 413–433 K. As a competing reaction with splitting of hydrogen from the DH, the isomerization of radicals R1 into ClCH(CH2)3CCl2H radicals with 1,5-migration of hydrogen was chosen, for which log k (sec–1)=9.343 –10.56/2,303RT (kcal/mole) was calculated. It was found that the relative reactivities are similar of R1 and (CH3)3CO radicals (R4) in splitting hydrogen from HD. This makes it possible to predict the values of analogous constants for radicals R1 from known rate constants of splitting hydrogen from various DH by radicals R4. The rate constants of the addition of Cl(CH2)2Cl2 radicals (R2) to amethylstyrene and methyl methacrylate were determined. Taking into account the data in [7], where the same constants were determined for styrene, methyl acrylate, acrylonitrile and vinyl methyl ketone, the existence of a linear dependence was shown of the logarithm of the rate constant of the addition of radicals R2 to olefins on the polar properties of the above-enumerated olefins.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1811–1816, August, 1990.The authors wish to express their gratitude to T. T. Vasil'eva for providing the reference samples of 1,5,5-trichloropentane and 1,1,5,5-tetrachloropentane.  相似文献   

11.
The foundations of the theoretical concept of nonbranched radical-chain reactions involving heterogeneous catalysts are considered for hydrocarbon pyrolysis. These include the phenomenological model and the concept of the catalysis sphere. Surface active sites S participate in chain propagation along with hydrocarbon radicals R· from the gas phase. Surfaces show either inhibiting or neutral action depending on the E S–R bond energy. If the E S–R value is comparable with the energy of the breaking bond in the reacting molecule, the reaction accelerates due to the acceleration of either the heterogeneous or homogeneous component of the overall rate of the process. In the latter case, the catalyst ensures the generation of additional radicals for the gas phase, which result in the formation of a catalysis sphere. The catalysis sphere is defined, the radical distribution in it is presented, and its properties and role in radical-chain processes are discussed.  相似文献   

12.
The hydration of the carboxylate group in the acetate anion has been investigated by performingab initio molecular orbital calculations on selected conformers of complexes with the form CH3CO2 ·nH2mH2O, wheren andm denote the number of water molecules in the first and second hydration spheres around the carboxylate group, andn + m 7. The results of RHF/6–31G* optimizations for all the complexes and MP2/6–31+G** optimizations for several one-water complexes are reported. The primary consequence of hydration on the structure of the acetate anion is a decrease in the length of the C-C bond. Enthalpy and free energy changes calculated at the MP2/6–31+G** and MP2/6–311+ +G** levels are reported for the reactions CH3CO2 + [H2O] P CH3CO2 ·nH2O ·mH2O where [H2O] P is a water cluster containingp water molecules andp=n+m 7. The calculations show that conformers with the lowest enthalpy change on complex formation are often not those with the lowest free energy change, due to a greater entropic loss in complexes with tighter and more favorable enthalpic interactions. Hydrogen bonding of six water molecules directly to the carboxylate group in CH3CO2 is found to account for approximately 40% of the enthalpy change and 37% of the free energy change associated with bulk solvation.  相似文献   

13.
The possibility of application of linear free energy relationships for studying the effects of substituents on the first vertical ionization potentials of amines, I(nN), was substantiated. The I(nN) values depend on the inductive, resonance, and polarizability effects of substituents and are also affected by hyperconjugation. The R + resonance parameters of substituents MR3 (M = Si, Ge, Sn) and CH2SiMe3 bound to the N ·+ radical cation center were calculated for the first time.  相似文献   

14.
The rate constants of the addition of CCl3CH2ClCH3(R6) radicals to -methyl-styrene, styrene, methyl methacrylate, methyl acrylate, and acrylonitrile and of CCl3CH2(CH3)2(R7) radicals to styrene, methyl acrylate, and acrylonitrile were determined by ESR spectroscopy. It was shown that the radicals R6 and R7 possess approximately equal reactivity in addition to unsaturated compounds, despite the difference in the donor-acceptor properties of the substituents at the vinyl group. In a comparison of the reactivity of radicals R6 and R7 with the reactivity of radicals CCl3CH2H2(R1), CCl3CH2HCH3(R3), CCl3CH2HCl(R4), and ClCH2CH2Cl2(R5) [1] in addition reactions, it was shown that polar and steric effects of the substituents situated in the -position to the radical site of the above-mentioned radicals, as well as the donor-acceptor properties of the substituents at the vinyl group in the unsaturated compounds, lead to appreciable changes in reactivity.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 136–141, January, 1992.  相似文献   

15.
Zusammenfassung -Substituierte -Acylvinylphosphonate3 mitE-Konfiguration [R 2CO-CH=C(R 1)-P(O)(OR)2], werden in guten Ausbeuten durchWittig-Reaktion von Acylphosphonsäureestern1 [R 1CO-P(O)(OR)2,R 1=Alkyl oder Aryl] mit (2-Oxoalkyliden)triphenylphosphoranen2 [R 2CO-CH=PPh 3,R 2=Alkyl, O-Alkyl oder CH2 X (X=Br, OMe, CO2 Et)] erhalten.
A convenient route to -substituted dialkyl (E)-3-oxo-1-alkenylphosphonates
-Substituted dialkyl (E)--acylvinylphosphonates [R 2CO-CH=C(R 1)-P(O)(OR)2,3], are easily obtained in good yields byWittig-reaction of dialkyl acylphosphonates1 [R 1CO-P(O)(OR)2,R 1=alkyl or aryl) with 2-oxoalkylidene triphenylphosphoranes2 [R 2CO-CH=PPh 3,R 2=alkyl, O-alkyl and CH2 X (X=Br, OMe, CO2 Et)].
  相似文献   

16.
A comparative investigation of thermodynamic and kinetic properties of a number of alkylaryl intermediates (benzyl and benzhydryl radicals) and alkyl halide intermediates (chloromethyl, dichloromethyl, and trifluoromethyl radicals) is performed by methods of laser photoemission. Techniques, aimed at the determination of thermodynamic and kinetic properties of intermediates (standard potentials E 0 of redox pairs R/R-, standard adsorption free energies -G a(R) 0 , values of rate constants W 0 at an equilibrium potential, as well as lifetimes (times of death in the bulk) R of radicals R and X of products of their reduction R-) from a comparison of Tafel plots for quasi-reversible reduction of intermediates with calculated ones and standard potentials E 0—from Tafel plots for irreversible electroreduction of intermediates, are presented. The transition from irreversible to quasi-reversible reduction in aprotic solvents at EE 0 is observed only in the case of benzyl, benzhydryl, and trifluoromethyl radicals, for which this particular collection of thermodynamic and kinetic properties is obtained, and is not observed for the chloromethyl and dichloromethyl radicals. In this case redox characteristics of intermediates (E 0, W 0) are estimated from absolute values of rates of their electroreduction. Possible reasons for the differences in the probability of a reversible electron transfer are discussed for the systems studied.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 157–174.Original Russian Text Copyright © 2005 by Krivenko, Kotkin, Kurmaz.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.  相似文献   

17.
The reaction of UO2(ClO4nH2O with 15-crown-5 and 18-crown-6 in acetonitrile yielded the title complexes. [UO2(OH2)5] [ClO4]2·3(15-crown-5)·CH3CN crystallizes in the triclinic space groupPT with (at–150°C)a=8.288(6),b=12.874(7),c=24.678(7) Å, =82.62(4), =76.06(5), =81.06(5)°, andD calc=1.67 g cm–3 forZ=2 formula units. Least-squares refinement using 6248 independent observed reflections [F o5(F o)] led toR=0.111. [UO2(OH2)5] [ClO4]2·2(18-crown-6)·2CH3CN·H2O is orthorhombicP212121 with (at–150 °C)a=12.280(2),b=17.311(7),c=22.056(3) Å,D calc=1.68 g cm–3,Z=4, andR=0.032 (3777 observed reflections). In each complex the crown ether molecules are hydrogen bonded to the water molecules of the pentagonal bipyramidal [UO2(OH2)5]2+ ions, each crown ether having exclusive use of two hydrogen atoms from one water molecule and one hydrogen from another water molecule. In the 15-crown-5 complex the remaining hydrogen bonding interaction is between one of the water molecules and one of the perchlorate anions. The solvent molecule has a close contact between the methyl group and a perchlorate anion suggesting a weak interaction. There are a total of three U-OH...OClO3 hydrogen bonds to the two perchlorate anions in [UO2(OH2)5] [ClO4]2·(18-crown-6)·2CH3CN ·H2O. The remaining coordinated water hydrogen bond is to the uncoordinated 2H2O molecule, which in turn is hydrogen bonded to a perchlorate oxygen atom and an acetonitrile nitrogen atom. One solvent methyl group interacts with an anion, the other with one of the 18-crown-6 molecules. Unlike the 15-crown-5 structure, the hydrogen bonding in this complex results in a polymeric network with formula units joined by hydrogen bonds from one of the solvent molecules and the uncoordinated water molecule. Supplementary data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82051 (37 pages).For Part 10, see reference [1].  相似文献   

18.
The transition state of addition of free radicals and atoms to multiple bonds is considered as a result of intersecting of two parabolic potential curves. One of them characterizes the stretching vibration of the attacked multiple bond, and another curve characterizes the stretching vibration of the bond formed in the transition state. The force constant of the latter is calculated by an empirical equation that correlates the force constant with the bond dissociation energy. In the framework of this model, the thermally neutral activation energy (E e0) and the elongation of the attacked and formed bonds (r e) in the transition state were calculated from the experimental data (activation energy (E e) and enthalpy of reaction (H e)) for the addition of an H atom and methyl, alkoxyl, aminyl, triethylsilyl, and peroxyl radicals to the C=C bond and the addition of H and CH3 to the C=O and CC bonds. Analysis of the data obtained showed that E e0 depends linearly on the |H e| + Ee sum, i.e., Ee0/kJ mol–1 = 14.2 + 0.61 · (EeH e), and the bond elongation in the transition state for addition of the most part of radicals to ethylene and acetylene vary within (0.65–0.87)·10–10 m. The factors affecting the activation energy of the radical addition reactions are discussed.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1542–August, 2004.  相似文献   

19.
Treatment of the different kinds of alkynyl-substituted dialkynyldiarylsilanes with zirconocene-ethylene complex Cp2Zr(CH2CH2) followed by acidification with 3 N HCl gave regio- and stereoselectively the corresponding silacyclobutenes in good yields. Desilylation of the silacyclobutenes with tetrabutylammonium fluoride afforded stereoselectively unsymmetrical conjugated (1E,3E)-dienes and -trienes (R1 or R2 = 1-cyclohexenyl) in excellent yields.  相似文献   

20.
Organosilicon gels [Co(NH2R2)2Cl2] and [Cr(NH2R2)3Cl3], containing a diaminodichloride complex of cobalt(II) and triaminotrichloride complex of chromium(III) (R2 = CH2CH2CH2SiO(OEt)), were synthesized by the hydrolysis of complexes [Co(NH2R1)2Cl2] (I) and [Cr(NH2R1)3Cl3] (II) incorporating peripheral triethoxysilyl groups (R1 = CH2CH2CH2Si(OEt)3). The coprecipitated [Co(NH2R2)2Cl2] · 4NH2R3, [Cr(NH2R2)3Cl3] · 6NH2R3, [Co(NH2R2)2Cl2] · 2SiO2, and [Cr(NH2R2)3Cl3] ·xSiO2 · (3 – x)SiHO1.5 (R3 = CH2CH2CH2SiO1.5) gels were obtained by cohydrolysis of complexes I and II with 3-aminopropyltriethoxysilane or triethoxysilane. Interaction with SiH(OEt)3 is accompanied by the decomposition of silicon hydride groups and the formation of tetraethoxysilane derivatives. The heating of dry gels in a flow of argon or oxygen to 600° results in the formation of amorphous silica having a specific surface area 2–467 m2/g and containing crystalline metals, their chlorides, oxides, silicates, or carbides.  相似文献   

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