首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 734 毫秒
1.
Sum-over-states perturbation calculations within the INDO framework are reported for 24 1J(FC) and 34 3J(FC) couplings. In general, satisfactory agreement with the experimental data is obtained when the integral products SF2(O) SC2(O) and 〈r?3Fr?3C take the values of 136.543 au?6 and 58.352 au?6, respectively, for the 1J(FC) couplings. The corresponding values for the 3J(FC) couplings are 29.520 au?6 and 44.340 au?6, respectively. All of the 1J(FC) values are predicted to be negative, whereas all of the 3J(FC) values are calculated with positive signs. The results indicate the importance of including the contact, orbital and dipolar contributions in the calculations.  相似文献   

2.
Self-consistent perturbation calculations within the INDO framework are reported for 63 15N? 13C coupling constants. Examples are presented for which each of the contact, orbital and dipolar terms provides the dominant contribution to the observed coupling constant. In general, good agreement with the experimental data is obtained when the integral products SN2(O)SC2(O) and 〈r?3N〈r?3C take the values 14.480 au?6 and 2.446 au?6 for 1J(15N? 13C), and the corresponding values of 10.444 au?6 and 17.664 au?6 for 1J(15N?13C). All 19 of the 1J(15N?13C) couplings considered are predicted to have a negative sign.  相似文献   

3.
1J(15N13C) values obtained from FT 13C NMR spectra were measured for a number of 15N-enriched aniline derivatives and are found to exhibit varying degrees of dependence on the nature of the ring substituent. Theoretical calculations of 1J(15N13C) values for representative members of the systems examined were made using INDO parameters and a ‘sum-over-states’ perturbation approach. The calculated coupling constants are generally in fair agreement with experimental values when the integral products SN2(o)SC2(o) and (r?3)N(r?3)C have values of 34.437 au?6 and 2.770 au?6, respectively.  相似文献   

4.
The high-pressure absolute rate constants for the decomposition of nitrosobenzene and pentafluoronitrosobenzene were determined using the very-low-pressure pyrolysis (VLPP) technique. Bond dissociation energies of DH0(C6H5? NO) = 51.5 ± 1 kcal/mole and DH0 (C6F5? NO) = 50.5 ± 1 kcal/mole could be deduced if the radical combination rate constant is set at log kr(M?1·sec?1) = 10.0 ± 0.5 for both systems and the activation energy for combination is taken as 0 kcal/mole at 298°K. δHf0(C6H5NO), δHf0(C6F5NO), and δHf0(C6F5) could be estimated from our kinetic data and group additivity. The values are 48.1 ± 1, –160 ± 2, and – 130.9 ± 2 kcal/mole, respectively. C–X bond dissociation energies of several perfluorinated phenyl compounds, DH0(C6F5–X), were obtained from the reported values of δHf0(C6F5X) and our estimated δHf0(C6F5) [X = H, CH3, NO, Cl, F, CF3, I, and OH].  相似文献   

5.
Pulsed laser photolysis, time-resolved laser-induced fluorescence experiments have been carried out on the reactions of CN radicals with CH4, C2H6, C2H4, C3H6, and C2H2. They have yielded rate constants for these five reactions at temperatures between 295 and 700 K. The data for the reactions with methane and ethane have been combined with other recent results and fitted to modified Arrhenius expressions, k(T) = A′(298) (T/298)n exp(?θ/T), yielding: for CH4, A′(298) = 7.0 × 10?13 cm3 molecule?1 s?1, n = 2.3, and θ = ?16 K; and for C2H6, A′(298) = 5.6 × 10?12 cm3 molecule?1 s?1, n = 1.8, and θ = ?500 K. The rate constants for the reactions with C2H4, C3H6, and C2H2 all decrease monotonically with temperature and have been fitted to expressions of the form, k(T) = k(298) (T/298)n with k(298) = 2.5 × 10?10 cm3 molecule?1 s?1, n = ?0.24 for CN + C2H4; k(298) = 3.4 × 10?10 cm3 molecule?1 s?1, n = ?0.19 for CN + C3H6; and k(298) = 2.9 × 10?10 cm3 molecule?1 s?1, n = ?0.53 for CN + C2H2. These reactions almost certainly proceed via addition-elimination yielding an unsaturated cyanide and an H-atom. Our kinetic results for reactions of CN are compared with those for reactions of the same hydrocarbons with other simple free radical species. © John Wiley & Sons, Inc.  相似文献   

6.
Chain transfer constants (Cs) for a number of substrates containing the silicon-oxygen bond are measured in polymerizing methyl methacrylate. Additionally, a few measurements are run in styrene in order to estimate the influence of polar factors on chain transfer. The methylsiloxanes studied all show very low values of Cs (10?5 to 10?6). The chain transfer constants of a number of propylsiloxane derivatives are negligibly influenced by the presence of silicon. Thus, (Me3SiO)2MeSiCH2MeCH(C6H5) shows a value of Cs nearly that reported for cumene, and (MeO)3SiCH2CH2CH2SH shows values of Cs close to those reported for alkyl mercaptans.  相似文献   

7.
By combining Hartree–Fock results for nonrelativistic ground-state energies of N-electron atoms with analytic expressions for the large-dimension limit, we have obtained a simple renormalization procedure. For neutral atoms, this yields energies typically threefold more accurate than the Hartree–Fock approximation. Here, we examine the dependence on Z and N of the renormalized energies E(N, Z) for atoms and cations over the range Z, N = 2 → 290. We find that this gives for large Z = N an expansion of the same form as the Thomas–Fermi statistical model, E → Z7/2(C0 + C1Z?1/3 + C2Z?2/3 + C3Z?3/3 + ?), with similar values of the coefficients for the three leading terms. Use of the renormalized large-D limit enables us to derive three further terms. This provides an analogous expansion for the correlation energy of the form δE δZ4/3(δC3 + δC5Z?2/3 + δC6Z?3/3 + ?); comparison with accurate values of δE available for the range Z ? 36 indicates the mean error is only about 10%. Oscillatory terms in E and δE are also evaluated. © 1994 John Wiley & Sons, Inc.  相似文献   

8.
We show that electron transfer from the perchlorotriphenylmethide anion (PTM?) to Y@C82(C2v) is an instantaneous process, suggesting potential applications for using PTM? to perform redox titrations of numerous endohedral metallofullerenes. The first representative of a Y@C82‐based salt containing the complex cation was prepared by treating Y@C82(C2v) with the [K+([18]crown‐6)]PTM? salt. The synthesis developed involves the use of the [K+([18]crown‐6)]PTM? salt as a provider of both a complex cation and an electron‐donating anion that is able to reduce Y@C82(C2v). For the first time, the molar absorption coefficients for neutral and anionic forms of the pure isomer of Y@C82(C2v) were determined in organic solvents with significantly different polarities.  相似文献   

9.
Standard INDO parameters are used in ‘sum-over-states’ perturbation calculations of nJ(NC) in a variety of molecular environments. Good agreement with the experimental data is, in general, obtained when the integral products SN2(o)SC2(o) and 〈r?3Nr?3C assume the values of 35.167 a.u.?3 and 4.980 a.u.?3, respectively. For ‘pyridine-type’ nitrogen atoms the major contribution to nJ(NC) usually arises from the orbital term whereas the contact term dominates the values of nJ(NC) for ‘pyrrole-type’ and amino nitrogen atoms.  相似文献   

10.
Abstract— In this research, we measured the short- and long-term, stem elongation responses of wild-type and aurea(au) mutant tomato plants to different photosynthetically active radiation (PAR) levels by using linear voltage transducers. Stem elongation was continuously measured in green tomato plants over 2.75 days, under 12 h light/12 h dark photoperiods or in darkness after a 6 h irradiation period. There is no significant difference in stem elongation between wild-type plants pregrown at either LOO or 400 μmol m?2 s?1 and then exposed to 12 h photoperiods. However, in the au mutant there is a very large difference between plants pregrown under 100 or 400 umol m ?2 s?1 and then exposed either to 12 h photoperiods or to continuous darkness. Total stem elongation of the wild type appears to be maximal at 100 umol m?2 s?1, while that of the au mutant appears to be maximal with PAR 400 umol m?2 s?1. Wild-type plants displayed PAR-dependent (in the range 100-800 umol m?2 s?1) inhibition of growth both during the day and during the night. In contrast, the au mutant showed a fluence-rate-dependent promotion of growth during the dark periods in the range of 10-400 umol m?2 s?1. Large, fast and opposite changes in stem elongation rate at the light/dark and dark/light transitions were present in both genotypes. Internode elongation rate in the first half of the night was always modest in wild-type tomato, whereas it increased rapidly in the au mutant. Stem elongation rate of wild type starts to increase after about 6 h in darkness, showing the typical time course of escape from Pfr-mediated inhibition of elongation by an end-of-day response. The role of phytochrome level and type in sensing light quantity is discussed.  相似文献   

11.
After a set of 32 free radicals was presented (Int J Chem Kin 34, 550–560, 2002), an additional 60 free radicals (Set‐2) were studied and characterized by energy minimum structures, harmonic vibrational wave numbers ωe, moments of inertia IA, IB, and IC, heat capacities Cop(T), standard entropies So(T), thermal energy contents Ho(T) ? Ho(0), and standard enthalpies of formation ΔfHo(T) at the G3MP2B3 level of theory. Thermodynamic functions at T = 298.15 K are presented and compared with recent experimental values where these are available. The mean absolute deviation between calculated and experimental ΔfHo(298.15) values by the previous set of 32 radicals is 3.91 kJ mol?1. For the sake of comparison, only 49 species out of the 60 radicals of Set‐2 are characterized by experimental enthalpies of formation, and the corresponding mean absolute deviation between calculated and experimental ΔfHo(298.15) values is 8.96 kJ mol?1. This situation is cause for demand of more and also more accurate experimental values. In addition to the above properties, parent molecules of a large set of the respective radicals are calculated to obtain bond dissociation energies Do(298.15). Radical stabilization owing to resonance is discussed using the complete sets of total atomic spin densities ρ as a support. In particular, a short review about recent developments of the first‐order Jahn–Teller radical c‐C5H5? is presented. In addition, radicals with negative bond energies are described, such as ?CH2OOH where the reaction path to CH2O + HO? has been calculated, as well as radicals which have two different parent molecules, for example C?N? O?. For the reaction HO? + CO → H? + CO2, two reaction paths are characterized by a total of 14 stationary points where the intermediate radicals HO? ?CO and HC(O)O? are involved. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 661–686, 2004  相似文献   

12.
The kinetics of ozonation of C2H4 and C2H2 have been studied in the gas phase from ?40 to ?95°C (C2H4) and +10 to ?30°C (C2H2). The O3 concentrations were near 10?4 M, and the hydrocarbons were present in 2- to 25-fold excess. A few experiments with propylene were also carried out. The reactions were followed by observing the rate of decay of O3 absorption at 2537 Å. Reaction stoichiometries and effects of added O2 were investigated. The second-order rate constant for C2H4 was log k(M?1 sec?1) = (6.3 ± 0.2) – (4.7 ± 0.2)/θ (θ = 2.3RT). The rate was independent of the presence of excess O2. Rate measurements for C3H6 were less accurate because of aerosol interference. Combined with room temperature measurements of other workers, the C3H6 rate constant was log k(M?1 sec?1) = (6.0 ± 0.4) – (3.2 ± 0.6)/θ. The C2H2 rate constant was log k(M?1 sec?1) = (9.5 ± 0.4) – (10.8 ± 0.4)/θ. In the case of C3H6 the major product was propylene ozonide. Ethylene did not yield the ozonide, and the products of the O3–C2H4 and O3–C2H2 reactions were not identified. Pre-exponential factors for the olefin reactions are consistent with a five-membered ring transition state formed by 1,3 dipolar cycloaddition of O3. For C2H2, however, the much higher observed A factor suggests a different mechanism. Possible transition states for the O3–C2H2 reaction are discussed.  相似文献   

13.
Pulsed gradient spin‐echo (PGSE) diffusion characteristics for a) the new [brucinium][X] salts 6 a – f [ a : X=BF4?; b : X=PF6?; c : X=MeSO3?, d : X=CF3SO3?; e : X=BArF?; f : X=PtCl3(C2H4)?], b) 4‐tert‐butyl‐N‐benzyl analogue, 7 and c) the aryl carbocations (p‐R‐C6H4)2CH 9 a (R=CH3O) and 9 b (R=(CH3)2N), (p‐CH3O‐C6H4)xCPh3?x+ 10 a – c (x=1–3, respectively) and (p‐R‐C6H4)3C+ 11 (R=(CH3)2N) and 12 (R=H) all in several different solvents, are reported. The solvent dependence suggests strong ion pairing in CDCl3, intermediate ion pairing in CD2Cl2 and little ion pairing in [D6]acetone. 1H, 19F HOESY NMR spectra (HOESY: heteronuclear Overhauser effect spectroscopy) for 6 and 7 reveal a specific approach of the anion with respect to the brucinium cation plus subtle changes, which are related to the anion itself. Further, for carbocations 9 – 12 , (all as BF4? salts) based on the NOE results, one finds marked changes in the relative positions of the BF4? anion. In these aryl cationic species the anion can be located either a) very close to the carbonium ion carbon b) in an intermediate position or c) proximate to the N or O atom of the p‐substituent and remote from the formally positive C atom. This represents the first example of such a positional dependence of an anion on the structure of the carbocation. DFT calculations support the experimental HOESY results. The solid‐state structures for 6 c and the novel Zeise's salt derivative, [brucinium][PtCl3(C2H4)], 6 f , are reported. Analysis of 195Pt NMR and other NMR measurements suggest that the η2‐C2H4 bonding to the platinum centre in 6 f is very similar to that found in K[PtCl3(C2H4)]. Field dependent T1 measurements on [brucinium][PtCl3(C2H4)] and K[PtCl3(C2H4)], are reported and suggested to be useful in recognizing aggregation effects.  相似文献   

14.
A series of novel cationic gemini surfactants, p-[C n H2n+1N+(CH3)2CH2CH(OH)CH2O]2C6H4·2Cl? [A(n = 12), B(n = 14) and C(n = 16)], containing a spacer group with two flexible and hydrophilic groups (2-hydroxy-1,3-propylene) on both sides of a rigid and hydrophobic group (1,4-dioxyphenylene) has been synthesized by the reaction of hydroquinone diglycidyl ether with N,N-dimethylalkylamine and N,N-dimethylalkylamine hydrochloride. Their surface-active properties have been investigated by surface tension measurement. The critical micelle concentration (cmc) values of the synthesized cationic gemini surfactants are one order of magnitude lower than those of their corresponding monomeric surfactants (C n H2n + 1N+(CH3)3·Cl?). Both the cmc and surface tension at the cmc (γcmc) of A are lower than those of p-[C12H25N+(CH3)2CH2]2C6H4·2Cl? (D). The novel cationic gemini surfactants A and B also show good foaming properties.  相似文献   

15.
The kinetics of the gas-phase reaction of Cl atoms with CF3I have been studied relative to the reaction of Cl atoms with CH4 over the temperature range 271–363 K. Using k(Cl + CH4) = 9.6 × 10?12 exp(?2680/RT) cm3 molecule?1 s?1, we derive k(Cl + CF3I) = 6.25 × 10?11 exp(?2970/RT) in which Ea has units of cal mol?1. CF3 radicals are produced from the reaction of Cl with CF3I in a yield which was indistinguishable from 100%. Other relative rate constant ratios measured at 296 K during these experiments were k(Cl + C2F5I)/k(Cl + CF3I) = 11.0 ± 0.6 and k(Cl + C2F5I)/k(Cl + C2H5Cl) = 0.49 ± 0.02. The reaction of CF3 radicals with Cl2 was studied relative to that with O2 at pressures from 4 to 700 torr of N2 diluent. By using the published absolute rate constants for k(CF3 + O2) at 1–10 torr to calibrate the pressure dependence of these relative rate constants, values of the low- and high-pressure limiting rate constants have been determined at 296 K using a Troe expression: k0(CF3 + O2) = (4.8 ± 1.2) × 10?29 cm6 molecule?2 s?1; k(CF3 + O2) = (3.95 ± 0.25) × 10?12 cm3 molecule?1 s?1; Fc = 0.46. The value of the rate constant k(CF3 + Cl2) was determined to be (3.5 ± 0.4) × 10?14 cm3 molecule?1 s?1 at 296 K. The reaction of Cl atoms with CF3I is a convenient way to prepare CF3 radicals for laboratory study. © 1995 John Wiley & Sons, Inc.  相似文献   

16.
A dodecaholmium wheel of [Ho12(L)6(mal)4(AcO)4(H2O)14] ( 1 ; mal=malonate) was synthesized by using ptert‐butylsulfonylcalix[4]arene (H4L) as a cluster‐forming ligand. The wheel consists of three fragments of mononuclear A3? ([Ho(L)(mal)(H2O)]3?), trinuclear B3? ([Ho(H2O)2(mal)(Ho(L)(AcO))2]3?), and C3+ ([Ho(H2O)2]3+), and an alternate arrangement of these fragments (A3?? C3+? B3?? C3+? A3?? C3+? B3?? C3+? ) results in a wheel structure. The longest and shortest diameters of the core were estimated to be 17.7562(16) and 13.6810(13) Å, respectively, and the saddle‐shaped molecule possesses a pocketlike cavity inside.  相似文献   

17.
Homoleptic perhalophenyl derivatives of divalent nickel complexes with the general formula [NBu4]2[NiII (C6X5)4] [X=F ( 1 ), Cl ( 2 )] have been prepared by low‐temperature treatment of the halo‐complex precursor [NBu4]2[NiBr4] with the corresponding organolithium reagent LiC6X5. Compounds 1 and 2 are electrochemically related by reversible one‐electron exchange processes with the corresponding organometallate(III) compounds [NBu4][NiIII (C6X5)4] [X=F ( 3 ), Cl ( 4 )]. The potentials of the [NiIII (C6X5)4]?/[NiII (C6X5)4]2? couples are +0.07 and ?0.11 V for X=F or Cl, respectively. Compounds 3 and 4 have also been prepared and isolated in good yield by chemical oxidation of 1 or 2 with bromine or the amminium salt [N(C6H4Br‐4)3][SbCl6]. The [NiIII (C6X5)4]? species have SP‐4 structures in the salts 3 and 4 , as established by single‐crystal X‐ray diffraction methods. The [NiII (C6F5)4]2? ion in the parent compound 1 has also been found to exhibit a rather similar SP‐4 structure. According to their SP‐4 geometry, the NiIII compounds (d7) behave as S=1/2 systems both at microscopic (EPR) and macroscopic levels (ac and dc magnetization measurements). The spin Hamiltonian parameters obtained from the analysis of the magnetic behavior of 3 and 4 within the framework of ligand field theory show that the unpaired electron is centered mainly on the metal atom, with >97 % estimated d contribution. Thermal decomposition of 3 and 4 proceeds with formation of the corresponding C6X5? C6X5 coupling compounds.  相似文献   

18.

An approach is proposed for analysing the deviations of the heat capacity Cp(T) of solid solutions from the Kopp–Neumann rule (KNR) ΔC(T)?=?Cp(T)???CKNR(T). Temperature dependences of the heat capacity Cp(T) of selected compositions of systems (InP)x (InAs)1?x and (GaAs)x (InAs)1?x at temperatures of 5–300 K are analysed in the Debye–Einstein approximation. It was established that in the case of substitution of atoms in the cation subsystem (Ga3+???In3+) with the same subsystem of anions (As3?), the positive values of ΔC(T) at T?<?100 K are due to the appearance of the low-frequency Einstein mode, whereas the negative values of ΔC(T) at T?>?100 K are the result of a decrease in the fraction of the Debye contribution without changing the upper limit of the oscillation frequency. In the case of substitution in the cation subsystem (P3????As3?) with the invariant cation subsystem (In3+) to the low-temperature positive contribution of the additional low-frequency Einstein mode, a positive part is added from the modified Debye mode having the characteristic temperature θD below the additive value θDKNR. The adequacy of this model is confirmed by Raman scattering data.

  相似文献   

19.
C2(a 3πu) disappearance rate constants of 1.44, 0.96, 0.0296, 0.0130 and < 10?6(x10?10cm3s?1) are reported for reactions with C2H4, C2H2, O2, C2H6, and CH4, respectively at 298 K. C2(a 3πu) fragments are generated by multiphoton ArF excimer laser photodissociation at C2H2, and monitored by dye laser induced fluorescence. Arguments are presented which favor chemical reactions over the C2(a 3πu) → (X 1σ+g) quenching channel. C2 + C2H2 represents the one possible exception to the reactive channel.  相似文献   

20.
The sequential addition of CN? or CH3? and electrophiles to three perfluoroalkylfullerenes (PFAFs), Cs‐C70(CF3)8, C1‐C70(CF3)10, and Csp‐C60(CF3)2, was carried out to determine the most reactive individual fullerene C atoms (as opposed to the most reactive C?C bonds, which has previously been studied). Each PFAF reacted with CH3? or CN? to generate metastable PFAF(CN)? or PFAF(CH3)22? species with high regioselectivity (i.e., one or two predominant isomers). They were treated with electrophiles E+ to generate PFAF(CN)(E) or PFAF(CH3)2(E)2 derivatives, also with high regioselectivity (E+=CN+, CH3+, or H+). All of the predominant products, characterized by mass spectrometry and 19F NMR spectroscopy, are new compounds. Some could be purified by HPLC to give single isomers. Two of them, C70(CF3)8(CN)2 and C70(CF3)10(CH3)2(CN)2, were characterized by single‐crystal X‐ray diffraction. DFT calculations were used to propose whether a particular reaction is under kinetic or thermodynamic control.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号