Time-resolved photoionization mass spectrometry in the millisecond range has been employed to study the reaction C6H5OCH+3 → C6H+6 + CH2O in anisole. Photoionization efficiency (PIE) curves gave a long-time limiting appearance energy value, AE = 10.85 ± 0.05 eV at 298 K. Experimental PIE curves and breakdown graphs at t = 6 μs and 2 ms were compared to those predicted by the statistical theory (RRKM/QET) and by previous photoelectron—photoion coincidence spectrometry results. A sensitivity analysis yielded the following activation parameters: critical energy of activation, E0 = 59.6 ± 0.6 kcal/mol, and entropy of activation, ΔS3(1000 K) = 7.25 ± 2.2 eu. 相似文献
Equilibria among the cyclic compounds (Me2Si)n where n = 5, 6 and 7 have been studied between 30–58°C. Thermodynamic values for the redistribution reactions between pairs of compounds are, for n = 5 → 6, ΔH = ?18 kcal/mole, ΔS = ?20 cal/deg. mole; for n = 7 → 6, ΔH ?3, ΔS +33; for n = 7 → 5, ΔH +18, ΔS + 51. The enthalpies indicate that the stabilities of the rings increase in the order (Me2Si)5 < (Me2Si)7 < (Me2Si)6. The differences are smaller than corresponding differences among the cycloalkanes, probably because the silicon compounds are less affected by steric repulsions and angle strain. 相似文献
Enthalpies, ΔH(1) ?94.8 ± 6.0 and ΔH(6) ?57.1 ± 5.1 kJ mol?1, of the following reactions have been measured calorimetrically [Pt(trans-stilbene)(PPh3)2](s) + dpcp(g) → (PPh3)2Pt(dpcb)(s) + trans-stilbene(g) (1) [Pt(trans-stilbene)(PPh3)2](s) + bcbd(g) → (PPh3)2Pt(bcpd)(s) + trans-stilbene (g) (6) where dpcp is diphenylcyclopropenone, (PPh3)2Pt(dpcb) is (1,1-bistriphenylphosphine)platinadiphenylcyclobutenone, (PPh3)2O, bcbd is benzocyclobutene-1,2-dione and (PPh3)2Pt(bcpd) is (1,1-bistriphenylphosphine)platinabenzocyclopentanedione, . It is concluded that the five-membered platinacyclo ring system in (PPh3)2Pt(dpcb) is not heavily strained. 相似文献
The reagent obtained by mixing anhydrous FeCl3 and silica gel induced, in the lack of any solvent, dehydration of tertiary cycloalkanols, specific C4→C5 and C5 →C6 enlargement, formation of spiro compounds and propella-γ- lactones and cleavage of tetrahydropyranyl ethers. 相似文献
The reactions of 1and 2butyne with O(3P) were studied at 298 K by means of a CO laser resonant absorption technique. The CO formedO(3P)+CH3CH2CCH→CC3H6H3CH2CH+COO(3P)+CH3CCCH3→CH3CC3H6CH3+COFrom the kinetic modeling of the observed rates of CO formation, the rates of these reactions were found to be 5.0 × 1011 and 1.6 × 1012 ml 相似文献
Rate coefficients for proton transfer reactions of the type XH+ + H2O → H3O+ + X where X = H2, CH4, CO, N2, CO2 and N2O and the type H2O + X? → XH + OH? where X = H, NH2 and C2H5NH have been measured at 297 K using the flowing afterglow technique. The results compare favourably with the predictions of the average-dipole-orientation theory. A trend is observed with exothermicity on a plot of (kexp/kADO)298 K versus ?ΔH298 K0. The question is raised whether the relatively low probability observed for slightly exothermic proton transfer reactions is a consequence of reaction mechanism or results from the presence of a small activation energy barrier. 相似文献
The high temperature pyrolysi of 1,3-butadiene has been investigated in the shock tube with two time-resolved diagnostic techniques: laser schlieren measurements of density gradient with 1, 2, 4, and 5% C4H6 in Ar or Kr, 0.26 < P2 < 0.66 atm, over 1550–2200 K, and time-of-flight mass spectra for 3% C4H6–Ne, P5 ~ 0.4 atm, 1400–2000 K. When combined with a recent single-pulse shock tube product analysis covering 1050–2050 K, these measurements permit a complete modeling of major species in C4H6 pyrolysis. Extrapolated density gradients and product analyses show initiation is dominated by C4H6 → 2C2H3., significant falloff and Arrhenius curvature being seen in the derived rates. A restricted rotor, Gorin model RRKM fit to these rates with reasonable parameters generates The derived barrier, ΔH = 99 ± 4 kcal/mol, translates to ΔH,298 = 63.4 ± 2 kcal/mol for the heat of formation of vinyl radical. A mechanism for the formation of all products detected in the above experiments is given, together with a successful but semiquantitative kinetic model for major products. The measurements require the rate of vinyl radical dissociation, C2H3 + M → C2H2 + H + M, to be extremely low, k < 109 cm3/mol s for 1600 K, so that the dominant chain carrier in C4H6 pyrolysis is vinyl radical. 相似文献
The transition linewidth ΔE in crystal C6H6, C6D6 and sym-C6H3D3 has been measured as a function of temperature T from 4.2 to 135°K, and it extrapolates to a common value of ΔEo = 50 cm? at O°K. In C6H6 ΔE = (50 + 7T) cm?1, indicative of strong exciton—phonon coupling, and there is a line shift of +40 cm?1 per substituent deuteron. Fluorescence excitation spectral data are used to separate the 1B1u(= S2) decay rate kH = 9.4 × 1012 sec?1, derived from ΔE0, into S2S1 internal conversion (rate ≈ 6.6 × 1012 sec?1) and S2Sx (channel 3) internal conversion (rate ≈ 2.8 × 1012 sec?1. A similar value of kH = 9.9 × 1012 sec?1 is obtained from the S2So fluorescence quantum yield of liquid benzene. 相似文献
An additive scheme with 11 constants is derived from the coefficients of characteristic polynomials (CCPs) of adjacency matrix A of irregular molecular graphs (IMG) for molecules that contain a bivalent heteroatom -SH or -OH at the beginning of the chain. The structural significance of the CCPs to adjacency matrix A′ is established. Our formula is used to calculate the enthalpies of formation ΔfHliq 298K○ of liquid alkanethiols (mercaptanes) CnH2n + 1SH and ΔfHliq 298K○ of liquid saturated monoalcohols CnH2n + 1OH that remain unstudied experimentally. 相似文献
The complexation of Y3+, La3+, and nd Hg2+ cations with macrocyclic ligands, dicyclohexyl-18-crown-6 (DCH18C6) and 15-crown-5 (15C5) have been studied in acetonitrile (AN)-N,N-dimethylformamide (DMF) binary solutions at different temperatures using conductometric method. The conductance data revealed 1: 1 [ML] stoichiometry for most complexes in pure DMF and AN-DMF binary solutions, except for the (DCH18C6-Y3+) complex in pure AN (1: 2, [ML2]). The stability constants of DCH18C6-La3+ and 15C5-La3+ in pure AN were higher than in pure DMF at all temperatures. Nonlinear behavior was observed for the stability constants of complexes against the composition of AN-DMF binary solutions at all temperatures. The minimum log Kf value for the 15C5-La3+ complex in AN-DMF binary solutions was obtained at χAN = 0.5, which may be due to negative excess viscosities ηE of AN-DMF mixtures over the whole composition range with a minimum value of χAN = 0.5. Moreover, the selectivity order of DCH18C6 and 15C5 for Y3+, La3+, and Hg2+ cations 25°C depended on the AN-DMF ratio. The thermodynamic parameters (ΔHC0) for complex formation were obtained from the temperature dependences of the stability constants of the complexes using the van’t Hoff plots, and the standard entropy (ΔSC0) was calculated from the relationship: ΔGC, 298.150 = ΔHC0 ? 298.15ΔSC0. 相似文献
Ionic liquid (IL) [C7mim][BF4] (1-heptyl-3-methyl-imidazolium tetrafluoroborate) was prepared and characterized. The density and surface tension of the IL were determined in the temperature range of 293.15–343.15 K. In terms of Glasser's theory, the standard molar entropy and lattice energy of the IL were estimated. Using Kabo's method, the molar enthalpy of vaporization of the IL, ΔlgHm0 (298 K), was estimated. According to the interstice model, the thermal expansion coefficient of IL, α, was calculated and in comparison with experimental value, they are within one order of magnitude. 相似文献
The reaction of molecular carbon vapor with oxygen has been studied in a flowing system. For an equilibrium disitribution of carbon molecular species at 2470 K, the dominant reaction observed was: C3 + O2 → C*2(d3II, ν′ = 1) + CO + O (or CO2). Of the product species, only excited C2 was detected. From these measurements a lower bound on the rate constant has been determined to be k ≥ 2 × 10?12 cm3/s. 相似文献
The product from reaction of samarium chloride hexahydrate with salicylic acid and Thioproline, [Sm(C7H5O3)2·(C4H6NO2S)]·2H2O, was synthesized and characterized by IR, elemental analysis, molar conductance, and thermogravimetric analysis. The standard molar enthalpies of solution of [SmCl3·6H2O(s)], [2C7H6O3(s)], [C4H7NO2S(s)] and [Sm(C7H5O3)2·(C4H7NO2S)·H2O(s)] in a mixed solvent of absolute ethyl alcohol, dimethyl sulfoxide(DMSO) and 3 mol L?1 HCl were determined by calorimetry to be ΔsHmΦ[SmCl3 δ6H2O (s), 298.15 K]= ?46.68±0.15 kJ mol?1 ΔsHmΦ[2C7H6O3 (s), 298.15 K]= 25.19±0.02 kJ mol?1, ΔsHmΦ[C4H7NO2S (s), 298.15 K]=16.20±0.17 kJ mol?1 and ΔsHmΦ[Sm(C7H5O3)2·(C4H6NO2S)]·2H2O (s), 298.15 K]= ?81.24±0.67 kJ mol?1. The enthalpy change of the reaction (1)$$ SmCl_3 \cdot 6H_2 O(s) + 2C_7 H_6 O_3 (s) + C_4 H_7 NO_2 S(s) = Sm(C_7 H_5 O_3 )_2 \cdot (C_4 H_6 NO_2 S) \cdot 2H_2 O(s) + 3HCl(g) + 4H_2 O(1) $$ was determined to be ΔsHmΦ =123.45±0.71 kJ mol?1. From date in the literature, through Hess’ law, the standard molar enthalpy of formation of Sm(C7H5O3)2(C4H6NO2S)δ2H2O(s) was estimated to be ΔsHmΦ[Sm(C7H5O3)2·(C4H6NO2S)]·2H2O(s), 298.15 K]= ?2912.03±3.10 kJ mol?1. 相似文献
The temperature dependence of the heat capacities of binuclear acetates M2(η1,η2-OOCCH3)2(η2-OOCCH3)4(H2O)4 · xH2O (M = La(1), Sm(2), Eu(3), and Tm(4)) (113?330 K); pivalates M2(μ2-OOCCMe3)4(OOCCMe3)2(HOOCCMe3)4·HOOCCMe3 (M=La(5), Sm(6), and Eu(7)) (113?320 K); and intermediate products of their thermal decomposition M2(OOCCH3)6(113–330 K) and M2(OOCCMe3)6 (113–500 K) and enthalpy changes at particular decomposition stages were determined by differential scanning calorimetry. The composition of the solid phase formed in decomposition was determined experimentally. The complete set of thermodynamic data was obtained, including Cp(T), S°(298), ΔfH°(298), and ΔfG°(298), for binuclear lanthanide acetates and pivalates specified above. The composition of the gas phase formed in decomposition was determined, which allowed us to suggest a resultant scheme of the thermal destruction of pivalates. The reliability of this scheme was demonstrated. 相似文献
Density functional theory was used to study model ethylene reactions with CpTiIIIEt+A? (A? = CH3B(C6F5)3?, or B(C6F5)4?; A? can be absent) compounds. The polymerization of ethylene on an isolated CpTiEt+ cation is hindered because of equilibrium between the CpTi(C2H4)Et+ primary complex and the primary product of CpTiBu+ insertion. At the same time, the polymerization of ethylene on CpTiEt+A? ion pairs (A? = CH3B(C6F5)3? or B(C6F5)4?) is thermodynamically allowed (ΔE from ?26.2 to ?25.6 kcal/mol and ΔG298 from ?10.9 to ?10.4 kcal/mol) and is not related to overcoming substantial energy barriers (ΔE# = 8.2?12.3 kcal/mol and ΔG298≠) = 7.8?13.3 kcal/mol). The degree of polymerization can be low because of the effective occurrence of polymer chain termination by hydrogen transfer from the polymer chain to the monomer. 相似文献
The fluorescence transitions corresponding to the second positive system of N2 (C3Πu → B3Πg) for Δv = 0, 1 and the first negative system of N+2(B2Σ+u → X2Σ+g) for Δv = 0, 1, 2 have been observed following laser-induced mul excitation of N2. 相似文献
The reactions of IO radicals with CH3SCH3, CH3SH, C2H4, and C3H6 have been studied using the discharge flow method with direct detection of IO radicals by mass spectrometry. The absolute rate constants obtained at 298 K are the following: IO + CH3SCH3 → products (1): k1 = (1.5 ± 0.2) × 10?14; IO + CH3SH → products (2): k2 = (6.6 ± 1.3) × 10?16; IO + C2H4 →products (3): k3 < 2 × 10?16; IO + C3H6 → products (4): k4 < 2 × 10?16 (units are cm3 molecule?1 s?1). CH3S(O)CH3 and HOI were found as products of reactions (1) and (2), respectively. The present lower value of k1 compared to our previous determination is discussed. 相似文献
Our attempts to synthesize the N→Si intramolecularly coordinated organosilanes Ph2L1SiH ( 1 a ), PhL1SiH2 ( 2 a ), Ph2L2SiH ( 3 a ), and PhL2SiH2 ( 4 a ) containing a CH?N imine group (in which L1 is the C,N‐chelating ligand {2‐[CH?N(C6H3‐2,6‐iPr2)]C6H4}? and L2 is {2‐[CH?N(tBu)]C6H4}?) yielded 1‐[2,6‐bis(diisopropyl)phenyl]‐2,2‐diphenyl‐1‐aza‐silole ( 1 ), 1‐[2,6‐bis(diisopropyl)phenyl]‐2‐phenyl‐2‐hydrido‐1‐aza‐silole ( 2 ), 1‐tert‐butyl‐2,2‐diphenyl‐1‐aza‐silole ( 3 ), and 1‐tert‐butyl‐2‐phenyl‐2‐hydrido‐1‐aza‐silole ( 4 ), respectively. Isolated organosilicon amides 1 – 4 are an outcome of the spontaneous hydrosilylation of the CH?N imine moiety induced by N→Si intramolecular coordination. Compounds 1–4 were characterized by NMR spectroscopy and X‐ray diffraction analysis. The geometries of organosilanes 1 a – 4 a and their corresponding hydrosilylated products 1 – 4 were optimized and fully characterized at the B3LYP/6‐31++G(d,p) level of theory. The molecular structure determination of 1 – 3 suggested the presence of a Si?N double bond. Natural bond orbital (NBO) analysis, however, shows a very strong donor–acceptor interaction between the lone pair of the nitrogen atom and the formal empty p orbital on the silicon and therefore, the calculations show that the Si?N bond is highly polarized pointing to a predominantly zwitterionic Si+N? bond in 1 – 4 . Since compounds 1 – 4 are hydrosilylated products of 1 a – 4 a , the free energies (ΔG298), enthalpies (ΔH298), and entropies (ΔH298) were computed for the hydrosilylation reaction of 1 a – 4 a with both B3LYP and B3LYP‐D methods. On the basis of the very negative ΔG298 values, the hydrosilylation reaction is highly exergonic and compounds 1 a – 4 a are spontaneously transformed into 1 – 4 in the absence of a catalyst. 相似文献
The gas phase thermal decomposition rates of C3-substituted peroxyacyl nitrates, RC(O)OONO2 have been measured at ambient temperature (287–298 K) and 1 atm. of air. Two saturated compounds (PnBN, R = n-C3H7- and PiBN, R = i-C3H7-) and two unsaturated compounds (MPAN, R = CH2=C(CH3)- and CPAN, R = CH3CH=CH-) have been studied. In the narrow temperature range studied, thermal decomposition rates for PiBN, PnBN and MPAN exhibited linear Arrhenius behavior with, in units of 10-4 s-1, and at 298 K, k = 2.2 for PiBN, 2.3 for MPAN, and 2.7 for PnBN. The thermal decomposition rate of CPAN was 1.6 x 10-4 s-1 at 291.6 K and 1.73 x 10-4 s-1 at 293.2 K. These thermal decomposition rates are of the same magnitude as that for PAN, R = CH3. Implications for the atmospheric persistence of C3- substituted peroxyacyl nitrates are briefly discussed. 相似文献