Cyclohexane and piperidine ring reversal in 1-(3-pentyloxyphenylcarbamoyloxy)-2-dialkylaminocyclohexanes was investigated by 13C NMR. An unusually low conformational energy ΔG = 0.59 kJ mol?1 and activation parameters ΔG≠218 = 43.8 ± 0.4 kJ mol?1, ΔH≠ = 48.9 ± 2.5 kJ mol?1 and ΔS≠ = 23 ± 9 J mol?1 K?1 were found for the diequatorial to diaxial transition of the cyclohexane ring in the trans-pyrrolidinyl derivative. In the trans-piperidinyl derivative, ΔG222 = 44.7 ± 0.5 KJ mol?1, ΔH≠ = 55.7 ± 6.3 kJ mol?1 and ΔS≠ = 51 ± 21 J mol?1 K?1 was found for the piperidine ring reversal from the non-equivalence of the α-carbons. 相似文献
The kinetics of the interactions between three sulfur‐containing ligands, thioglycolic acid, 2‐thiouracil, glutathione, and the title complex, have been studied spectrophotometrically in aqueous medium as a function of the concentrations of the ligands, temperature, and pH at constant ionic strength. The reactions follow a two‐step process in which the first step is ligand‐dependent and the second step is ligand‐independent chelation. Rate constants (k1 ~10?3 s?1 and k2 ~10?5 s?1) and activation parameters (for thioglycolic acid: ΔH1≠ = 22.4 ± 3.0 kJ mol?1, ΔS1≠ = ?220 ± 11 J K?1 mol?1, ΔH2≠ = 38.5 ± 1.3 kJ mol?1, ΔS2≠ = ?204 ± 4 J K?1 mol?1; for 2‐thiouracil: ΔH1≠ = 42.2 ± 2.0 kJ mol?1, ΔS1≠ = ?169 ± 6 J K?1 mol?1, ΔH2≠ = 66.1 ± 0.5 kJ mol?1, ΔS2≠ = ?124 ± 2 J K?1 mol?1; for glutathione: ΔH1≠ = 47.2 ± 1.7 kJ mol?1, ΔS1≠ = ?155 ± 5 J K?1mol?1, ΔH2≠ = 73.5 ± 1.1 kJ mol?1, ΔS2≠ = ?105 ± 3 J K?1 mol?1) were calculated. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. The products of the reactions have been characterized from IR and ESI mass spectroscopic analysis. A rate law involving the outer sphere association complex formation has been established as 相似文献
2D 1H-1H EXSY NMR spectroscopy show that the free energy of activation ΔG≠ in six 3-allyl-3-borabicyclo[3.3.1]nonane derivatives is significantly higher (72–86 kJ mol?1) than that in typical allylboranes (48–66 kJ mol?1). For the first member of the series, viz., 3-allyl-3-borabicyclo[3.3.1]nonane, the activation parameters of the permanent allylic rearrangement were also determined (ΔH≠ = 82.7±3.4 kJ mol?1, ΔS≠ = ?11.8±10.3 J mol?1 K?1, EA = 85.5±3.4 kJ mol?1, lnA = 29.2±1.2). 相似文献
An accurate gas-phase acidity for germane (enthalpy scale, equivalent to the proton affinity of GeH3?), ΔHacido(GeH4) = 1502.0 ± 5.1 kJ mol?1, is obtained by constructing a consistent acidity ladder between GeH4, and H2S by using Fourier transform-ion cyclotron resonance spectrometry, and 0 and 298.15 K values for the first bond dissociation energy of GeH4 are proposed: D0o(H3Ge-H) = 352 ± 9 kJ mol?1; Do(H3Ge-H) = 358 ± 9 kJ mol?1, respectively. These results are compared with experimental and theoretical data reported in the literature. Methylgermane was found to be a weaker acid than germane by approximately 35 kJ mol?1: ΔHacido = 1536.6 kJ mol?1. 相似文献
At room temperature and below, the proton NMR spectrum of N-(trideuteriomethyl)-2-cyanoaziridine consists of two superimposed ABC patterns assignable to two N-invertomers; a single time-averaged ABC pattern is observed at 158.9°C. The static parameters extracted from the spectra in the temperature range from –40.3 to 23.2°C and from the high-temperature spectrum permit the calculation of the thermodynamic quantities ΔH0 = ?475±20 cal mol?1 (?1.987 ± 0.084 kJ mol?1) and ΔS0 = 0.43±0.08 cal mol?1 K?1 (1.80±0.33 J mol?1 K?1) for the cis ? trans equilibrium. Bandshape analysis of the spectra broadened by non-mutual three-spin exchange in the temperature range from 39.4–137.8°C yields the activation parameters ΔHtc≠ = 17.52±0.18 kcal mol?1 (73.30±0.75 kJ mol?1), ΔStc≠ = ?2.08±0.50 cal mol?1 K?1 (?8.70±2.09 J mol?1 K?1) and ΔGtc≠ (300 K) = 18.14±0.03 kcal mol?1 (75.90±0.13 kJ mol?1) for the trans → cis isomerization. An attempt is made to rationalize the observed entropy data in terms of the principles of statistical thermodynamics. 相似文献
[RuCl2(NCCH3)2(cod)], an alternative starting material to [RuCl2(cod)]n for the preparation of ruthenium(II) complexes, has been prepared from the polymer compound and isolated in yields up to 87% using a new work-up procedure. The compound has been obtained as a yellow solid without water of crystallization. The complexes [RuCl2(NCR)2(cod)] spontaneously transform into dimers [Ru2Cl(μ-Cl)3(cod)2(NCR)] (R?=?Me, Ph). 1H NMR kinetic experiments for these transformations evidenced first-order behavior. [RuCl2(NCPh)2(cod)] dimerizes slower by a factor of ten than [RuCl2(NCCH3)2(cod)]. The following activation parameters, ΔH#?=?114?±?3?kJ?mol?1 and ΔS#?=?66?±?9?J?K?1?mol?1 for R?=?CH3CN (ΔG#?=?94?±?5?kJ?mol?1, 298.15?K) and ΔH#?=?122?±?2?kJ?mol?1 and ΔS#?=?75?±?6?J?K?1?mol?1 for R?=?Ph (ΔG#?=?100?±?4?kJ?mol?1, 298.15?K), have been calculated from the first-order rate constants in the temperature range 294–323?K. The kinetic parameters are in agreement with a two-step mechanism with dissociation of acetonitrile as the rate-determining step. The molecular structures of [Ru2Cl(μ-Cl)3(cod)2(NCR)] (R?=?Me, Ph) have been determined by X-ray diffraction. 相似文献
The addition of thioacetic acid to unsaturated alcohols or acids was utilized to obtain mercaptoalkanols which were condensed with suitable carybonyl compounds to prepare 24 methyl-substituted 1,3-oxathianes. The 1H NMR spectra of the 1,3-oxathiane products were recorded at 60, 100 and/or 300 MHz and fully analysed. The results are best explained by a chair form which is completely staggered in the C-4? C-5? C-6 moiety ψ45 or (ψ56=60±1°). 1,3-Oxathianes having syn-axial 2,4- (and/or 2,6-) methyl-methyl interactions exist appreciably, if not exclusively, in twist forms. The vicinal coupling constants lead to the conformational free energies of axial methyl groups at C-4, ΔG°=7.4±0.4 kJ mol?1, and at C-5, ΔG°=3.7±0.3 kJ mol?1, in good agreement with previous estimates. They also show that both r-4,cis-5,trans-6- and r-4,trans-5,trans-6- trimethyl-1,3-oxathianes greatly favour the chiar form where the methyl group at C-4 is axial. The chair-twist energy parameters are reestimated at ΔH°CT 27.0 kJ mol?1, ΔS°CT 11.6J mol?1K?1, and ΔG°CT(298) 23.5 kJ mol?1 for a 2,5-twist form. 相似文献
From measurements of the heats of iodination of CH3Mn(CO)5 and CH3Re(CO)5 at elevated temperatures using the ‘drop’ microcalorimeter method, values were determined for the standard enthalpies of formation at 25° of the crystalline compounds: ΔHof[CH3Mn(CO)5, c] = ?189.0 ± 2 kcal mol?1 (?790.8 ± 8 kJ mol?1), ΔHof[Ch3Re(CO)5,c] = ?198.0 ± kcal mol?1 (?828.4 ± 8 kJ mo?1). In conjunction with available enthalpies of sublimation, and with literature values for the dissociation energies of MnMn and ReRe bonds in Mn2(CO)10 and Re2(CO)10, values are derived for the dissociation energies: D(CH3Mn(CO)5) = 27.9 ± 2.3 or 30.9 ± 2.3 kcal mol?1 and D(CH3Re(CO)5) = 53.2 ± 2.5 kcal mol?1. In general, irrespective of the value accepted for D(MM) in M2(CO)10, the present results require that, D(CH3Mn) = D(MnMn) + 18.5 kcal mol?1 and D(CH3Re) = D(ReRe) + 30.8 kcal mol?1. 相似文献
Restricted rotation about the naphthalenylcarbonyl bonds in the title compounds resulted in mixtures of cis and trans rotamers, the equilibrium and the rotational barriers depending on the substituents. For 2,7-dimethyl-1,8-di-(p-toluoyl)-naphthalene (1) ΔH° = 3.66 ± 0.14 kJ mol?1, ΔS° = 1.67 ± 0.63 J mol?1 K?1, ΔH≠ct = 55.5 ± 1.3 kJ mol?1, ΔH≠ct = 51.9 ± 1.3 kJ mol?1, ΔS≠ct = ?41.3±4.1 J mol?1 K?1 and ΔS≠ct = ?42.9±4.1 J mol?1 K?1. The rotation about the phenylcarbonyl bond requires ΔH≠ = ?56.9±4.4 kJ mol?1 and ΔS≠ = ?20.5±15.3 J mol?1 K?1 for the cis rotamer, and ΔH≠ = 43.5Δ0.4 kJ mol?1 and ΔS≠ =± ?22.4Δ1.3 J mol?1 K?1 for the trans rotamer. The role of electronic factors is likely to be virtually the same for both these rotamers but steric interaction between the two phenyl rings occurs in the cis rotamer only. Hence, the difference of the activation enthalpies obtained for the cis and trans rotamers, ΔΔH?1 = 13.4 kJ mol?1, provides a basis for the estimation of the role of steric factors in this rotation. For the tetracarboxylic acid 2 and its tetramethyl ester 3 the equilibrium is even more shifted towards the trans form because of enhanced steric and electrostatic interactions between the substituents in the cis form. The barriers for the rotation around the phenylcarbonyl bond and the cis-trans isomerization are lowered; an explanation for this result is presented. 相似文献
The enthalpies of reaction 1–3 have been determined as ΔH(1) = ?176.6 ± 5.4, ΔH(2) = ?107.8 ± 6.0, and ΔH(3) = ?78.9 ± 2.0 kJ mol?1. The bond dissociation energy difference D1(PtCH3) ? D1(PtI) = +6 ± 5 kJ mol?1 is calculated, which indicates that the two bonds have very similar strengths. 相似文献
The determination of the dimerisation constant (KD) for the weak self-association of a compound C in dilute solution according to the equilibrium, 2C?C2 is described. The method uses chemical shifts measured on a series of solutions of C at different concentrations: the optimum KD is defined by a linear regression best-fit procedure, which simultaneously determines optimum values for δo and also for δ∞, the intrinsic chemical shifts for nuclei in the monomer and dimer species. The dimerisation of caffeine in D2O is used as a model to demonstrate the working of the method and the quality of results obtained. The most probable value of KD for caffeine at 30.5° is found in the range 5.5–6.0 kg solution · mol?1, and the enthalpy and entropy of dimerisation are found to be ΔH? = ?15.1 kJ · mol?1 and ΔS? = ?35.3 J · °C?1 · mol?1, respectively. The influence of small errors in δo on the confidence limits of KD is discussed. 相似文献