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1.
This study deals with the trichloroisocyanuric acid (TCCA) interactions with carboxamides like formamide (FMA), N,N′‐dimethyl formamide (DMF), and N,N′‐dimethyl acetamide (DMA) interactions during the nitration of heterocyclic compounds (HC) like pyrrole and indole in the presence of excess of [NaNO2] over the concentrations of all other reactants. All the reactions were performed in aqueous acetonitrile media containing carboxamide under acid‐free conditions. Kinetics of the reactions revealed first order in [nitrating agent] and [HC] under otherwise similar conditions. To gain an insight into the reactive species and role of added carboxamide (FAA, DMF, DMA, etc.), the observed rates of the nitration reaction (log k) were analyzed as a function of (1/D), ([D ? 1]/[2D + 1]), mole fraction (nx), and volume (%) of carboxamide, 1/viscosity, density refractive index function), and Hildebrand solubility parameter plots. Linear regression analysis gave very good correlation coefficients (R2 values), which indicate the importance of several solvent properties in addition to the role of dielectric constant (D) of the reaction media. Multiple linear solvent energy relationships suggested by Abraham, Koppel, Palm, and Taft also afforded very good correlation coefficient (R2 values), showing the importance of cumulative effect of solvent properties. Besides these features, the negative entropies of activation (?S#) suggest greater solvation in the transition state. Isokinetic temperature (β) values for different protocols were very close to the experimental temperature range (303‐323 K), indicating the importance of both enthalpy and entropy factors in controlling the reaction.  相似文献   

2.
We obtain an analytic expression for the total energy of a metallic cluster formed by N atoms of valence v and with net charge Q, by solving variationally the extended Thomas–Fermi version of density functional theory within the spherical jellium model. The energy is expressed as an expansion (mass formula) in decreasing powers of the cluster radius RI = rsZ1/3, with Z = vN, and rs, the one electron radius of the bulk, and the coefficients of this mass formula are functions of rs. Contributions of volume (RI3), surface (RI2), curvature (RI), constant (RI0), (1/RI), and (1/RI2) are clearly separated in the formula. The Chemical potential, work function, electron affinity, and ionization potential are easily obtained for neutral and charged clusters of any electronic density in the metallic range. A general estimation of the critical size for stability against electron detachment of negatively charged clusters is also obtained. The stability of highly charged clusters against fragmentation is also studied. © John Wiley & Sons, Inc.  相似文献   

3.
4.
The crosslinking processes of aqueous poly(vinyl alcohol) (PVA) by γ‐ray irradiation were studied by viscometry, dynamic and static light scattering (DLS and SLS), as well as size exclusion chromatography (SEC). Increases in the intrinsic viscosity ([η]), molecular weight (Mw), hydrodynamic radius (Rh), and radius of gyration (Rg), and a decrease in second virial coefficient (A2) were observed after γ‐ray irradiation. However, both the values of [η] and A2 for irradiated PVA fell below the data of unirradiated PVA solutions, suggesting a conformational change of PVA chains after γ‐ray irradiation. This structural change of PVA as a result of γ‐ray irradiation was also indicated by the decreases in Rg/Rh from 1.5 to 1.39 by SLS and DLS, and in Mark–Houwink exponent αη from 0.54 to 0.26 by SEC‐Viscometry. The broadening of the Mw distribution (MWD) as indicated by the polydispersity index increased from 2.2 to 6.5 because of γ‐ray irradiation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 214–221, 2000  相似文献   

5.
Summary. Salt effects on kinetics of oxidation and decomposition of novel low-spin Fe(II) complexes of azo amino acids with hydrogen peroxide have been investigated in aqueous medium. The ligands are derived from amino acids (DL-phenylalanine, DL-tryptophane, histidine, and alanine) and p-nitroso aromatic substituted amines (N,N-dimethyl-4-nitrosoaniline and N,N-diethyl-4-nitrosoaniline). Hydrophobic salts of alkali metal and tetraalkylammonium halides, e.g., KBr, tetrabutylammonium bromide (TBAB), tetraethylammonium bromide (TEAB), and tetramethylammonium bromide (TMAB) have been used. Dilute salt solutions exhibit little effects on the reactivities of oxidation and decomposition of the title compounds. This behaviour would be ascribed to a decrease in the activity coefficients of the reacting species in these solutions. Moreover, these effects support the reported pathway in these reactions occurring via the association of dicationic complexes and undissociated H2O2. On the other hand, higher salt concentration shows considerable effects on the reactivities. This behaviour is explained in terms of hydrophilicity of the complexes, ion pair formation, salting out, and substituent effects. Hyrophilic nature of the recent complexes enhances reactivity with increasing [KBr] due to salting out effects in the aqueous medium. Increasing [TBAB] retards reactivity via ion pair formation with the reactants. In the presence of R4N+ ions, the reactivity increases with changing R in the following order; R = C4H9 < C2H5 < CH3. The bulky R groups in the added tetraalkylammonium salts, exert medium steric hindrance against the approach of reactants.  相似文献   

6.
Salt effects on kinetics of oxidation and decomposition of novel low-spin Fe(II) complexes of azo amino acids with hydrogen peroxide have been investigated in aqueous medium. The ligands are derived from amino acids (DL-phenylalanine, DL-tryptophane, histidine, and alanine) and p-nitroso aromatic substituted amines (N,N-dimethyl-4-nitrosoaniline and N,N-diethyl-4-nitrosoaniline). Hydrophobic salts of alkali metal and tetraalkylammonium halides, e.g., KBr, tetrabutylammonium bromide (TBAB), tetraethylammonium bromide (TEAB), and tetramethylammonium bromide (TMAB) have been used. Dilute salt solutions exhibit little effects on the reactivities of oxidation and decomposition of the title compounds. This behaviour would be ascribed to a decrease in the activity coefficients of the reacting species in these solutions. Moreover, these effects support the reported pathway in these reactions occurring via the association of dicationic complexes and undissociated H2O2. On the other hand, higher salt concentration shows considerable effects on the reactivities. This behaviour is explained in terms of hydrophilicity of the complexes, ion pair formation, salting out, and substituent effects. Hyrophilic nature of the recent complexes enhances reactivity with increasing [KBr] due to salting out effects in the aqueous medium. Increasing [TBAB] retards reactivity via ion pair formation with the reactants. In the presence of R4N+ ions, the reactivity increases with changing R in the following order; R = C4H9 < C2H5 < CH3. The bulky R groups in the added tetraalkylammonium salts, exert medium steric hindrance against the approach of reactants.  相似文献   

7.
Using a real space implementation of the self‐consistent field theory, we calculated the morphology and interactions of spherical nanoparticles with radius Rp that are grafted by polymer chains of N monomers immersed in a chemically identical polymer melt of polymerization index P. The calculation shows that, for big particles (Rp ? N1/2a, with a the segment size), the interactions and density profiles of the grafted layers are that of brushes at flat interface; While for small particles (Rp ? N1/2a), the interactions and density profiles are characteristic of star polymers. In the case of intermediate grafted chain lengths, that is, RpN1/2a, we found that the grafting density of the polymers and the radius of the spherical nanoparticles are both important in determining the structure and interactions of the grafted layers. Our findings suggest possible ways to tailor the structure and interactions of the nanoparticles to benefit the fabrication of polymeric nanocomposites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2811–2820, 2006  相似文献   

8.
Synchrotron small-angle X-ray scattering technique has been used to study the effect of ultrasound on the microstructure of polystyrene (PS) in cyclohexane solutions. The results show that the intramolecular radius of gyration (R g) decreases with ultrasound, indicating the shrinkage and collapse of PS chains. There is an exponential relationship between R g and the molecular weight of PS (M w), and the exponent changes from 0.5 to 0.417, as the ultrasound time is increased. This means that the shape of PS chain changes from random coil to shrunken form. The Kratky plots also confirm the shape transformation of PS chains induced by ultrasound. Moreover, the intermolecular correlation length increases with the ultrasound time, which is indicative of the entanglement of PS chains.  相似文献   

9.
Some new 1,2,4-triazole derivatives have been synthesized and characterized by TLC, IR, NMR and mass spectra. Densities, viscosities and ultrasonic velocities of these compounds have been measured over the wide composition range at 308.15?K in dimethyl formamide (DMF) and tetrahydro furan (THF). From these data, various acoustical and thermodynamic parameters (C.V. Suryanarayana, J. Kuppuswamy. J. Acoust. Soc. Ind., 4, 75 (1976); H. Erying, M.S. John, Significance of Liquid Structures, Wiley, New York (1969); G.K. Johri, R.C. Misra. Acustica, 56, 66 (1989)) were evaluated. Some of these parameters are isentropic compressibility (κs), intermolecular free length (L f), relaxation strength (r), relative association (R A), Rao's molar constant (R m), van der Waal's constant (b), molar compressibility (W), internal pressure (π), free volume (V f), solvation number (S n) etc. The behavior of solutions of these compounds in DMF and THF are explained from the evaluated parameters.  相似文献   

10.
Summary. Photoredox reactions occurring in irradiated methanolic solutions of trans-[Fe(N 2 O 2 ) (CH3OH)N3], where N 2 O 2 2– are tetradentate open-chain N 2 O 2 -Schiff base N,N-ethylenebis(R-salicylaldiminato) or N,N-1-methylethylenebis(R-salicylaldiminato) ligands denoted as R-salen and R-sal(Me)en, respectively (R=H, 5-Cl, 5-Br, 4-OCH3), have been investigated and their mechanism has been proposed. The complexes are redox stable in the dark. Ultraviolet and/or visible irradiation of methanolic solutions of the complexes induces photoreduction of Fe(III) to Fe(II). As an intermediate, CH2OH radicals were identified by EPR spin trapping technique. The final product of the photooxidation coupled with the photoreduction of Fe(III) is formaldehyde. The efficiency of the photoredox processes is strongly wavelength dependent and influenced by the peripheral groups R of the tetradentate ligands. Differences between the course of photochemical changes induced by 254nm radiation and the other wavelengths of incident radiation is rationalized by involving azide anions photoreactivity in observed redox changes.  相似文献   

11.
傅强 《高分子科学》2002,(2):143-154
Crystallization in polymer systems actually is a process that transfers the entangled melts into a semi-crystallinelayered structure. Whether or not a chain disentangles may result in different crystallization mechanism. When compared tothe crystal thickness (d_c), the volume occupied by the chain in the melt, i.e., the radius of gyration (R_g), plays a veryimportant role in polymer crystallization. When d_c≤R_g, crystallization does not necessitate a chain disentangling. Theentanglements are just shifted into the amorphous regions. However, as d_c>R_g, i.e., as the crystal thickness ges larger thanthe radius of gyration of the chain in the melt, it becomes necessary for a chain to disentangle. Then a change ofcrystallization mechanism occurs. Such change has been experimentally observed in the crystallization of poly(1-butene). Achange in the crystal morphologies from spherulite to quadrangle, is seen via PLM, as crystalliation temperatures increase.Even more, such a change is molecular weigh dependent and shifts to lower temperature as molecular weigh decreases.There exists a jump of crystal thickness and crystallinity associated with morphological change, as seen via SAXS. A changeof crystallization kinetics and crystallinity is further evidenced via dilatometry. The unique feature of P1b crystallization hasbeen discussed based on the radius of gyration of chain in the melt (R_g), and very good agreement is obtained.  相似文献   

12.
The conformation of hyperbranched polymers from one pot polymerization with ABn (n = 2, 4) type monomers, applying the reactive 3D bond fluctuation lattice model, are systematically studied using scaling relation RNλ, where R is the radius of gyration or the hydrodynamic radius of a hyperbranched polymer with the degree of polymerization N. The exponent λ was calculated at various monomer concentrations and group conversions. When the concentration of monomers with the equal reactivity of B groups increases from 0.1 to 0.9, the exponents λg and λh (corresponding to the radius of gyration and hydrodynamic radius, respectively) are in the ranges of 0.51–0.37 and 0.41–0.34 at the full conversion of A groups. Especially, we find that λg decreases linearly with the reaction conversion increasing. The ratio of z‐average radius, Rgz/Rhz, ranges from 1.08 to 1.32 and indicates that hyperbranched polymer is soft macromolecule with penetrable structure. In the case of AB2 type monomer with unequal reactivities, λ displays complicated dependence on the reaction conversion and the reactivity ratio. The results of our simulation are consistent with those of experiments and theories, and valuable in better understanding the fundamental properties of hyperbranched polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 610–616, 2010  相似文献   

13.
Solvation of the thallous ion in dilute solutions of six binary solvent systems (formamide/water,N-methylformamide/water,N-ethylformamide/water, formamide/N-methylformamide, formamide/N-ethylformamide, andN-methylformamide/N-ethylformamide) was studied with205Tl NMR spectroscopy. An attempt was made to separate solvation effects related to the electrondonating ability (Lewis basicity) of the solvents from effects resulting from structural changes in the solvation sphere. Structural effects were found to be greatest in theN-methylformamide/water system and least in theN-methylformamide/formamide system.  相似文献   

14.
The use of CO2 as a massive and polarizable drift gas is shown to greatly improve peak‐to‐peak resolution (Rp‐p), as compared with N2, for the separation of disaccharides in a Synapt G2 traveling wave ion mobility cell. Near or baseline Rp‐p was achieved for three pairs of sodiated molecules of disaccharide isomers, that is, cellobiose and sucrose (Rp‐p = 0.76), maltose and sucrose (Rp‐p = 1.04), and maltose and lactose (Rp‐p = 0.74). Ion mobility mass spectrometry using CO2 as the drift gas offers therefore an attractive alternative for fast and efficient separation of isomeric disaccharides. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

15.
A series of potentially useful lithium amidinates and guanidinates were prepared and fully characterized. Treatment of N,N′‐diisopropylcarbodiimide with phenyllithium in diethyl ether afforded the lithium amidinate [PhC(NiPr)2Li(OEt2)]2 ( 1 ). Similar treatment of N,N′‐diorganocarbodiimides R′–N=C=N–R′ [R′ = iPr, cyclohexyl (Cy)] with secondary lithium amides LiNR2 [R2 = Et2, iPr2, (CH2)4] followed by crystallization from THF or 1,4‐dioxane gave the lithium guanidinates [R2NC(NR′)2Li(S)]2 [ 2 : R = Et, R′ = iPr, S = THF; 3 : R2 = (CH2)4, R′ = iPr, S = THF; 4 : R = R′ = iPr, S = ½ 1,4‐dioxane; 5 : R2 = (CH2)4, R′ = Cy, S = 1,4‐dioxane] as crystalline solids. Reaction of N‐lithioaziridine with the corresponding carbodiimides afforded solvent‐deficient [{C2H4NC(NiPr2)2}2Li2(THF)]2 ( 6 ), and [C2H4NC(NEt)(NtBu)Li(THF)]2 ( 7 ). Crystal structure determination revealed the presence of common ladder‐type dimeric structures for 1 – 5 . Compound 6 exists as a dimer of two ladder‐type dimers in the crystal, and 7 exhibits an unusual dimeric structure comprising an eight‐membered C2N4Li2 ring.  相似文献   

16.
The polymerization of methyl methacrylate (MMA) initiated by an enolizable ketone (R1? CO? CH2? CO? R2)-carbon black system was investigated. Although enolizable ketone itself could not do so, the polymerization of MMA was initiated by enolizable ketone in the presence of carbon black. In addition, a chloranil-enolizable ketone system was able to initiate the polymerization of MMA. It was found that the enol form of the ketone and quinonic oxygen groups on the carbon black surface played an important role in the initiation system; namely, it was considered that the polymerization was begun by the ketone radical (R1? CO? CH? CO? R2) formed by a one-electron transfer reaction from enolate ion to quinonic oxygen groups. The effect of solvent on the process was also studied. The rate of the polymerization increased, depending on the solvent used, in the following order: benzene < 1,4-dioxane < dimethyl sulfoxide < N,N-dimethylformamide < N-methyl-2-pyrrolidone. Furthermore, it became apparent that during the polymerization poly(methyl methacrylate) was grafted onto the carbon black surface (grafting ratio was ca. 40% when benzene was used as solvent) and the carbon black obtained gave a stable colloidal dispersion in organic solvent.  相似文献   

17.
The oxidative cyclization of the title compounds results in generally two different kinds of products. The first, 1-(N,N-bisacetylamino)-1,2,3-triazole 7 (R3 = CH3) is the primary product, while the second, 1-N-acetylamino-1,2,3-triazole 8 (R3 = CH3), when observed, is obtained via hydrolysis from the former during work-up and separation of the reaction mixture. The primary products are considered as resulting from intramolecular nucleophilic attack on the acetyl group, of the presumed zwitterionic intermediate 5 (R3 = CH3), by the N of the ambident N-acetylimine site of 5 .  相似文献   

18.
The density, viscosity, and ultrasonic velocity of solutions of two schiff bases in 1,4-dioxane and dimethylformamide (DMF) were measured at 318.15 K. Various acoustical properties, such as the specific impedance (Z), isentropic compressibility (κs), Rao’s molar sound function (R m), van der Waals constant (b), molar compressibility (W), intermolecular free length (L f), relaxation strength (r), relative association (R A), and free volume (V f), were calculated. The results were interpreted in terms of molecular interactions occurring in the solutions. Published in Russian in Zhurnal Fizicheskoi Khimii, 2006, Vol. 80, No. 7, pp. 1206–1210. The text was submitted by the authors in English.  相似文献   

19.
Intermediates relevant to cobalt-catalyzed alkene hydroformylation have been isolated and evaluated in fundamental organometallic transformations relevant to aldehyde formation. The 18-electron (R,R)-(iPrDuPhos)Co(CO)2H has been structurally characterized, and it promotes exclusive hydrogenation of styrene in the presence of 50 bar of H2/CO gas (1:1) at 100 °C. Deuterium-labeling studies established reversible 2,1-insertion of styrene into the Co−D bond of (R,R)-(iPrDuPhos)Co(CO)2D. Whereas rapid β-hydrogen elimination from cobalt alkyls occurred under an N2 atmosphere, alkylation of (R,R)-(iPrDuPhos)Co(CO)2Cl in the presence of CO enabled the interception of (R,R)-(iPrDuPhos)Co(CO)2C(O)CH2CH2Ph, which upon hydrogenolysis under 4 atm H2 produced the corresponding aldehyde and cobalt hydride, demonstrating the feasibility of elementary steps in hydroformylation. Both the hydride and chloride derivatives, (X=H, Cl), underwent exchange with free 13CO. Under reduced pressure, (R,R)-(iPrDuPhos)Co(CO)2Cl underwent CO dissociation to form (R,R)-(iPrDuPhos)Co(CO)Cl.  相似文献   

20.
In order to interpret well whether or not the organic or polymer interfacial layer is effective on performance of the conventional Au/n‐Si (metal semiconductor [MS]) type Schottky barrier diodes (SBDs), in respect to ideality factor (n ), leakage current, rectifying rate (RR ), series and shunt resistances (Rs , Rsh ) and surface states (Nss ) at room temperature, both Au/biphenyl‐CoPc/n‐Si (MPS1) and Au/OHSubs‐ZnPc/n‐Si (MPS2) type SBDs were fabricated. The electrical characteristics of these devices have been investigated and compared by using forward and reverse bias current–voltage (I–V ) characteristics in the voltage range of (?4 V)–(4 V) for with and without (biphenyl‐CoPc) and (OHSubs‐ZnPc) interfacial layers at room temperature. The main electrical parameters of these diodes such as reverse saturation current (I0 ), ideality factor (n ), zero‐bias barrier height (ΦB0 ), RR , Rs and Rsh were found as 1.14 × 10?5 A, 5.8, 0.6 eV, 362, 44 Ω and 15.9 kΩ for reference sample (MS), 7.05 × 10?10 A, 3.8, 0.84 eV, 2360, 115 Ω and 270 kΩ for MPS1 and 2.16 × 10?7 A, 4.8, 0.7 eV, 3903, 62 Ω and 242 kΩ for MPS2, respectively. It is clear that all of these parameters considerably change by using an organic interfacial layer. The energy density distribution profile of Nss was found for each sample by taking into account the voltage dependence of effective barrier height (Φe ) and ideality factor, and they were compared. Experimental results confirmed that the use of biphenyl‐CoPc and OHSubs‐ZnPc interfacial layer has led to an important increase in the performance of the conventional of MS type SBD. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

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