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1.
The values of the enthalpy (53.3; 51.3; 20.0 kJ mol?1), entropy (?106; ?122; ?144 J mol?1K?1), and volume of activation (?29.1; ?31.0; ?cm3 mol?1), the reaction volume (?25.0; ?26.6; ?cm3 mol?1) and reaction enthalpy (?155.9; ?158.2; ?150.2 kJ mol?1) have been obtained for the first time for the ene reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione 1 , with cyclohexene 4 , 1‐hexene 6 , and with 2,3‐dimethyl‐2‐butene 8 , respectively. The ratio of the values of the activation volume to the reaction volume (?VcorrVr ? n) in the ene reactions under study, 1 + 4 → 5 and 1 + 6 → 7 , appeared to be the same, namely 1.16. The large negative values of the entropy and the volume of activation of studied reactions 1 + 4 → 5 and 1 + 6 → 7 better correspond to the cyclic structure of the activated complex at the stage determining the reaction rate. The equilibrium constants of these ene reactions can be estimated as exceeding 1018 L mol?1, and these reactions can be considered irreversible. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2.
Solvent, temperature, and high pressure influence on the rate constant of homo‐Diels–Alder cycloaddition reactions of the very active hetero‐dienophile, 4‐phenyl‐1,2,4‐triazolin‐3,5‐dione (1), with the very inactive unconjugated diene, bicyclo[2,2,1]hepta‐2,5‐diene (2), and of 1 with some substituted anthracenes have been studied. The rate constants change amounts to about seven orders of magnitude: from 3.95.10?3 for reaction (1+2) to 12200 L mol?1 s?1 for reaction of 1 with 9,10‐dimethylanthracene (4e) in toluene solution at 298 K. A comparison of the reactivity (ln k2) and the heat of reactions (?r‐nH) of maleic anhydride, tetracyanoethylene and of 1 with several dienes has been performed. The heat of reaction (1+2) is ?218 ± 2 kJ mol?1, of 1 with 9,10‐dimethylanthracene ?117.8 ± 0.7 kJ mol?1, and of 1 with 9,10‐dimethoxyanthracene ?91.6 ±0.2 kJ mol?1. From these data, it follows that the exothermicity of reaction (1+2) is higher than that with 1,3‐butadiene. However, the heat of reaction of 9,10‐dimethylanthracene with 1 (?117.8 kJ mol?1) is nearly the same as that found for the reaction with the structural C=C counterpart, N‐phenylmaleimide (?117.0 kJ mol?1). Since the energy of the N=N bond is considerably lower (418 kJ/bond) than that of the C=C bond (611 kJ/bond), it was proposed that this difference in the bond energy can generate a lower barrier of activation in the Diels–Alder cycloaddition reaction with 1. Linear correlation (R = 0.94) of the solvent effect on the rate constants of reaction (1+2) and on the heat of solution of 1 has been observed. The ratio of the volume of activation (?V) and the volume of reaction (?Vr‐n) of the homo‐Diels–Alder reaction (1+2) is considered as “normal”: ?V/?Vr‐n = ?25.1/?30.95 = 0.81. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

3.
G3(MP2)//B3LYP calculations have been carried out on trans‐ and cis‐decalin, and their mono‐, di‐, tri‐, and tetraoxa‐analogs. The main purpose of the work was to obtain enthalpies of formation for these compounds, and to study the relative stabilities of the cistrans and positional isomers of the various (poly)oxadecalins. Comparison of the computational enthalpies of formation with the respective experimental ones, known only for the decalins and 1,3,5,7‐tetraoxadecalins, shows that in both cases the computational values are more negative than the experimental ones, the deviations being ?5 to ?7 kJ mol?1 for the decalins and ?12 to ?17 kJ mol?1 for the 1,3,5,7‐tetraoxadecalins. The respective computational enthalpies of cistrans isomerization, however, are in excellent to satisfactory agreement with the experimental data. The cistrans enthalpy differences vary from +11.0 kJ mol?1 for decalin to ?15.4 kJ mol?1 for 1,4,5,8‐tetraoxadecalin. Low relative enthalpy values were also calculated for the cis isomers of 1,8‐dioxadecalin (?3.7 kJ mol?1), 1,3,6‐trioxadecalin (?4.6 kJ mol?1), 1,3,8‐trioxadecalin (?9.7 kJ mol?1), 1,4,5‐ trioxadecalin (?5.6 kJ mol?1), 1,3,5,8‐tetraoxadecalin (?7.3 kJ mol?1), and 1,3,6,8‐tetraoxadecalin (?14.5 kJ mol?1). Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

4.
A homogeneous, molecular, gas‐phase elimination kinetics of 2‐phenyl‐2‐propanol and 3‐methyl‐1‐ buten‐3‐ol catalyzed by hydrogen chloride in the temperature range 325–386 °C and pressure range 34–149 torr are described. The rate coefficients are given by the following Arrhenius equations: for 2‐phenyl‐2‐propanol log k1 (s?1) = (11.01 ± 0.31) ? (109.5 ± 2.8) kJ mol?1 (2.303 RT)?1 and for 3‐methyl‐1‐buten‐3‐ol log k1 (s?1) = (11.50 ± 0.18) ? (116.5 ± 1.4) kJ mol?1 (2.303 RT)?1. Electron delocalization of the CH2?CH and C6H5 appears to be an important effect in the rate enhancement of acid catalyzed tertiary alcohols in the gas phase. A concerted six‐member cyclic transition state type of mechanism appears to be, as described before, a rational interpretation for the dehydration process of these substrates. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

5.
Based on energetic compound [1,2,5]‐oxadiazolo‐[3,4‐d]‐pyridazine, a series of functionalized derivatives were designed and first reported. Afterwards, the relationship between their structure and performance was systematically explored by density functional theory at B3LYP/6‐311 g (d, p) level. Results show that the bond dissociation energies of the weakest bond (N–O bond) vary from 157.530 to 189.411 kJ · mol?1. The bond dissociation energies of these compounds are superior to that of HMX (N–NO2, 154.905 kJ · mol?1). In addition, H1, H2, H4, I2, I3, C1, C2, and D1 possess high density (1.818–1.997 g · cm?3) and good detonation performance (detonation velocities, 8.29–9.46 km · s?1; detonation pressures, 30.87–42.12 GPa), which may be potential explosives compared with RDX (8.81 km · s?1, 34.47 GPa ) and HMX (9.19 km · s?1, 38.45 GPa). Finally, allowing for the explosive performance and molecular stability, three compounds may be suggested as good potential candidates for high‐energy density materials. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

6.
Kinetic parameters of the unusual [2π + 2σ + 2σ]‐cycloaddition reactions of quadricyclane ( 1 ) with tetracyanoethylene ( 2 ), 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione ( 3 ), N‐phenylmaleimide ( 4 ), and diethyl azodicarboxylate ( 5 ) are determined experimentally. Additionally, the enthalpies of 1  +  2 reaction in 1,4‐dioxane solution (?236.6 ± 1.0 kJ mol?1) and 1  +  3 reaction in toluene (?255.0 ± 2.8 kJ mol?1) are determined calorimetrically and shown to be the largest in absolute magnitude among all known cycloaddition reactions involving these dienophiles. Solvent effect on the rate of 1 + 3 reaction in 11 solvents is studied and found to be moderate and similar to that of the conventional Diels‐Alder and ene reactions. The difference in the reaction rate constants of 1 with different dienophiles can be up to 9 orders of magnitude and is mainly caused by the difference in activation enthalpies. This difference is not correlated with the standard enthalpies of reactions and is likely the result of high sensitivity of the [2π + 2σ + 2σ] reaction rates to the energy of donor‐acceptor interactions between the reactants.  相似文献   

7.
The conformational equilibria of 3‐methyl‐3‐silathiane 5 , 3‐fluoro‐3‐methyl‐3‐silathiane 6 and 1‐fluoro‐1‐methyl‐1‐silacyclohexane 7 have been studied using low temperature 13C NMR spectroscopy and theoretical calculations. The conformer ratio at 103 K was measured to be about 5 ax: 5 eq = 15:85, 6 ax: 6 eq = 50:50 and 7 ax: 7 eq = 25:75. The equatorial preference of the methyl group in 5 (0.35 kcal mol?1) is much less than in 3‐methylthiane 9 (1.40 kcal mol?1) but somewhat greater than in 1‐methyl‐1‐silacyclohexane 1 (0.23 kcal mol?1). Compounds 5–7 have low barriers to ring inversion: 5.65 (ax → eq) and 6.0 (eq → ax) kcal mol?1 ( 5 ), 4.6 ( 6 ), 5.1 (Meax → Meeq) and 5.4 (Meeq → Meax) kcal mol?1 ( 7 ). Steric effects cannot explain the observed conformational preferences, like equal population of the two conformers of 6 , or different conformer ratio for 5 and 7 . Actually, by employing the NBO analysis, in particular, considering the second order perturbation energies, vicinal stereoelectronic interactions between the Si–X and adjacent C–H, C–S, and C–C bonds proved responsible. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
The gas‐phase elimination kinetics of selected ethyl esters of 2‐oxo‐carboxylic acid have been studied over the temperature range of 270–415 °C and pressures of 37–114 Torr. The reactions are homogeneous, unimolecular, and follow a first‐order rate law in a seasoned static reaction vessel, with an added free radical suppressor toluene. The observed overall and partial rate coefficients are expressed by the following Arrhenius equations:
  • Ethyl oxalyl chloride
  • log koverall (s?1) = (13.22 ± 0.45) ? (179.4 ± 4.9) kJ mol?1 (2.303 RT)?1
  • Ethyl piperidineglyoxylate
  • log k(CO2) (s?1) = (12.00 ± 0.30) ? (191.2 ± 3.9) kJ mol?1 (2.303 RT)?1
  • log k(CO) (s?1) = (12.60 ± 0.09) ? (210.7 ± 1.2) kJ mol?1 (2.303 RT)?1
  • log kt(overall) (s?1) = (12.22 ± 0.26) ? (193.4 ± 3.4) kJ mol?1 (2.303 RT)?1
  • Ethyl benzoyl formate
  • log k(CO2) (s?1) = (12.89 ± 0.72) ? (203.8 ± 9.0) kJ mol?1 (2.303 RT)?1
  • log k(CO) (s?1) = (13.39 ± 0.31) ? (213.3 ± 3.9) kJ mol?1 (2.303 RT)?1
  • log kt(overall) (s?1) = (13.24 ± 0.60) ? (205.8 ± 7.6) kJ mol?1 (2.303 RT)?1
The kinetic and thermodynamic parameters of these reactions, together with those reported in the literature, lead to consider three different mechanistic pathways of elimination. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

9.
For magnesium perchlorate (MP), the solvent effect on the heat of solution and partial molar volumes (PMV) at 25 °C was studied. Since the complete dissociation of magnesium perchlorate is more difficult to achieve as compared with lithium perchlorate (LP), the concentration dependence of the values of the heat of solution and partial molar volume were noted. Only in highly polar solvents with large donor numbers (DN), such as water, dimethyl sulfoxide, N,N‐dimethyl formamide, and formamide, the differential and integral values of the enthalpies of solution were the same in the range of concentrations studied. In all solvents studied, the values of the heat of solution of MP were highly exothermic and exceed that of LP by more than 30 kcal mol?1. The values of the partial molar volume of MP were changed from 82.3 cm3 mol?1 in formamide to ?2.4 cm3 mol?1 in acetone, and correlate linearly with that of LP (R = 0.975). Taking into account the significant change in the properties of molecules in the solvate shell of cation Mg2+, the large increase in the reactivity of reactants, activated by such interaction with Mg2+ cation is expected. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

10.
The products formed in 2‐methoxytetrahydropyran elimination reaction in the gas phase are 3, 4‐dihydro‐2H‐pyran and methanol. The kinetic study was carried out in a static system, with the vessels deactivated with allyl bromide, and the presence of the free radical suppressor toluene. Temperature and pressure ranges were 400–450 °C and 25–83 Torr, respectively. The process is homogeneous, unimolecular, and follows a first‐order rate law. The observed rate coefficient is represented by the following equation: log k (s?1) = (13.95 ± 0.15) ? (223.1 ± 2.1) (kJ mol?1) (2.303RT)?1. The reactant exists mainly in two low energy chair‐like conformations, with the 2‐methoxy group in axial or equatorial position. However, the transition state (TS) for the elimination of the two conformers is the same. Theoretical calculations of this reaction were carried for two possible mechanisms from these conformations by using DFT functionals B3LYP, MPW1PW91, and PBE with the basis set 6‐31G(d,p) and 6‐31G++(d,p). The calculation results demonstrate that 2‐methoxytetrahydropyran exists mainly in two conformations, with the 2‐methoy group in axial or equatorial position, that are thermal in equilibrium. The average thermodynamic and kinetic parameters, taking into account the populations of the conformers in the equilibrium, are in good agreement with experimental values at B3LYP/6‐31++(d,p) level of theory. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

11.
The self‐association and tautomerism of (E)‐isatin‐3‐4‐phenyl(semicarbazone) Ia and (E)‐N‐methylisatin‐3‐4‐phenyl(semicarbazone) IIa were investigated in solvents of various polarity. In weakly interacting non‐polar solvents, such as CHCl3 and benzene, phenylsemicarbazone concentrations above 1×10?5 mol dm?3 result in the formation of dimers or higher aggregates of E‐isomers Ia and IIa . This aggregate formation prevents room temperature E–Z isomerization of Ia and IIa to more stable Z‐isomers. In contrast to the situation in non‐polar solvents, E–Z isomerization from the monomeric form of phenylsemicarbazone Ia and IIa E‐isomers occurs in highly interactive polar solvents including MeOH and DMF only at temperatures above 70 °C. Moreover, decrease in phenylsemicarbazone concentration below 1×10?4 mol dm?3 in these highly solute–solvent interacting systems leads to aggregate dissociation, and a new hydrazonol tautomeric form with a high degree of conjugation predominates in these solutions. Theoretical calculations confirm obtained experimental results. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

12.
The gas‐phase elimination of 1,1‐dimethoxycyclohexane yielded 1‐methoxy‐1‐cyclohexene and methanol. The kinetics were determined in a static system, with the vessels deactivated with allyl bromide, and in the presence of the free radical inhibitor cyclohexene. The working temperature was 310–360 °C and the pressure was 25–85 Torr. The reaction was found to be homogeneous, unimolecular, and follows a first‐order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equation: log k(s?1) = [(13.82 ± 0.07) – (193.9 ± 1.0)(kJ mol?1)](2.303RT)?1; r = 0.9995. Theoretical calculations were carried out using density functional theory (DFT) functionals B3LYP, MPW1PW91, and PBE with the basis set 6‐31G(d,p) and 6‐31G++(d,p). The calculated values for the energy of activation and enthalpy of activation are in reasonably good agreement with the experimental values using the PBE/6‐31G (d,p) level of theory. Both experimental results and theoretical calculations suggest a molecular mechanism involving a concerted polar four‐membered cyclic transition state. The transition state structure of methanol elimination from 1,1‐dimethoxycyclohexane is characterized by a significantly elongated C? O bond, while the Cβ? H bond is stretched to a smaller extent, as compared to the reactant. The process can be described as moderately asynchronic with some charge separation in the TS. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

13.
Reactions of . OH/O .? radicals, H‐atoms as well as specific oxidants such as N and Cl radicals with 4‐hydroxybenzyl alcohol (4‐HBA) in aqueous solutions have been investigated at various pH values using the pulse radiolysis technique. At pH 6.8, . OH radicals were found to react with 4‐HBA (k = 6 × 109 dm3 mol?1 s?1) mainly by contributing to the phenyl moiety and to a minor extent by H‐abstraction from the ? CH2OH group. . OH radical adduct species of 4‐HBA, i.e., . OH‐(4‐HBA) formed in the addition reaction were found to undergo dehydration to give phenoxyl radicals of 4‐HBA. Decay rate of the adduct species was found to vary with pH. At pH 6.8, decay was very much dependent on phosphate buffer ion concentrations. Formation rate of phenoxyl radicals was found to increase with phosphate buffer ion concentration and reached a plateau value of 1.6 × 105 s?1 at a concentration of 0.04 mol dm?3 of each buffering ion. It was also seen that . OH‐(4‐HBA) adduct species react with HPO ions with a rate constant of 3.7 × 107 dm3 mol?1 s?1 and there was no such reaction with H2PO ions. However, the rate of reaction of . OH‐(4‐HBA) adduct species with HPO ions decreased on adding KH2PO4 to the solution containing a fixed concentration of Na2HPO4 which indicated an equilibrium in the H+ removal from . OH‐(4‐HBA) adduct species in the presence of phosphate ions. In the acidic region, the . OH‐(4‐HBA) adduct species were found to react with H+ ions with a rate constant of 2.5 × 107 dm3 mol?1 s?1. At pH 1, in the reaction of . OH radicals with 4‐HBA (k = 8.8 × 109 dm3 mol?1 s?1), the spectrum of the transient species formed was similar to that of phenoxyl radicals formed in the reaction of Cl radicals with 4‐HBA at pH 1 (k = 2.3 × 108 dm3 mol?1 s?1) showing that . OH radicals quantitatively bring about one electron oxidation of 4‐HBA. Reaction of . OH/O .? radicals with 4‐HBA by H‐abstraction mechanism at neutral and alkaline pH values gave reducing radicals and the proportion of the same was determined by following the extent of electron transfer to methyl viologen. H‐atom abstraction is the major pathway in the reaction of O .? radicals with 4‐HBA compared to the reaction of . OH radicals with 4‐HBA. At pH 1, transient species formed in the reactions of H‐atoms with 4‐HBA (k = 2.1 × 109 dm3 mol?1 s?1) were found to transfer electrons to methyl viologen quantitatively. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

14.
The kinetics of cyclohexane (CyH) oxygenation with tert‐butyl hydroperoxide (TBHP) in acetonitrile at 50 °C catalysed by a dinuclear manganese(IV) complex 1 containing 1,4,7‐trimethyl‐1,4,7‐triazacyclononane and co‐catalysed by oxalic acid have been studied. It has been shown that an active form of the catalyst (mixed‐valent dimeric species ‘MnIIIMnIV’) is generated only in the interaction between complex 1 and TBHP and oxalic acid in the presence of water. The formation of this active form is assumed to be due to the hydrolysis of the Mn? O? Mn bonds in starting compound 1 and reduction of one MnIV to MnIII. A species which induces the CyH oxidation is radical tert‐BuO . generated by the decomposition of a monoperoxo derivative of the active form. The constants of the equilibrium formation and the decomposition of the intermediate adduct between TBHP and 1 have been measured: K = 7.4 mol?1 dm3 and k = 8.4 × 10?2 s?1, respectively, at [H2O] = 1.5 mol dm?3 and [oxalic acid] = 10?2 mol dm?3. The constant ratio for reactions of the monomolecular decomposition of tert‐butoxy radical (tert‐BuO . → CH3COCH3 + CH) and its interaction with the CyH (tert‐BuO . + CyH → tert‐BuOH + Cy . ) was calculated: 0.26 mol dm?3. One of the reasons why oxalic acid accelerates the oxidation is due to the formation of an adduct between oxalic acid and 1 (K ≈ 103 mol?1 dm3). Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

15.
The gas‐phase elimination kinetics of the title compounds were carried out in a static reaction system and seasoned with allyl bromide. The working temperature and pressure ranges were 200–280 °C and 22–201.5 Torr, respectively. The reactions are homogeneous, unimolecular, and follow a first‐order rate law. These substrates produce isobutene and corresponding carbamic acid in the rate‐determining step. The unstable carbamic acid intermediate rapidly decarboxylates through a four‐membered cyclic transition state (TS) to give the corresponding organic nitrogen compound. The temperature dependence of the rate coefficients is expressed by the following Arrhenius equations: for tert‐butyl carbamate logk1 (s?1) = (13.02 ± 0.46) – (161.6 ± 4.7) kJ/mol(2.303 RT)?1, for tert‐butyl N‐hydroxycarbamate logk1 (s?1) = (12.52 ± 0.11) – (147.8 ± 1.1) kJ/mol(2.303 RT)?1, and for 1‐(tert‐butoxycarbonyl)‐imidazole logk1 (s?1) = (11.63 ± 0.21)–(134.9 ± 2.0) kJ/mol(2.303 RT)?1. Theoretical studies of these elimination were performed at Møller–Plesset MP2/6‐31G and DFT B3LYP/6‐31G(d), B3LYP/6‐31G(d,p) levels of theory. The calculated bond orders, NBO charges, and synchronicity (Sy) indicate that these reactions are concerted, slightly asynchronous, and proceed through a six‐membered cyclic TS type. Results for estimated kinetic and thermodynamic parameters are discussed in terms of the proposed reaction mechanism and TS structure. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

16.
The gas‐phase elimination kinetics of tetrahydropyranyl phenoxy ethers: 2‐phenoxytetrahydro‐2H‐pyran, 2‐(4‐methoxyphenoxy)tetrahydro‐2H‐pyran, and 2‐(4‐tert‐butylphenoxy)tetrahydro‐2H‐pyran were determined in a static system, with the vessels deactivated with allyl bromide, and in the presence of the free radical inhibitor toluene. The working temperature and pressure were 330 to 390°C and 25 to 89 Torr, respectively. The reactions yielded DHP and the corresponding 4‐substituted phenol. The eliminations are homogeneous, unimolecular, and satisfy a first‐order rate law. The Arrhenius equations for decompositions were found as follows:
  • 2‐phenoxytetrahydro‐2H‐pyran
  • log k1 (s?1) = (14.18 ± 0.21) ? (211.6 ± 0.4) kJ mol?1 (2.303 RT)?1
  • 2‐(4‐methoxyphenoxy)tetrahydro‐2H‐pyran
  • log k1 (s?1) = (14.11 ± 0.18) ? (203.6 ± 0.3) kJ mol?1 (2.303 RT)?1
  • 2‐(4‐tert‐butylphenoxy)tetrahydro‐2H‐pyran
  • log k1 (s?1) = (14.08 ± 0.08) ? (205.9 ± 1.0) kJ mol?1 (2.303 RT)?1
The analysis of kinetic and thermodynamic parameters for thermal elimination of 2‐(4‐substituted‐phenoxy)tetrahydro‐2H‐pyranes suggests that the reaction proceeds via 4‐member cyclic transition state. The results obtained confirm a slight increase of rate constant with increasing electron donating ability groups in the phenoxy ring. The pyran hydrogen abstraction by the oxygen of the phenoxy group appears to be the determinant factor in the reaction rate.  相似文献   

17.
Ni20[(OH)12(H2O)6][(HPO4)8(PO4)4]·12H2O nanorods are successfully synthesized via a one‐pot hydrothermal reaction. A high‐performance flexible asymmetric all‐solid‐state supercapacitor based on the obtained Ni20[(OH)12(H2O)6][(HPO4)8(PO4)4]·12H2O nanorods (positive electrode) and graphene nanosheets (negative electrode) is successfully assembled. It is the first report of this nanomaterial applied for all‐solid‐state supercapacitors. Interestingly, a maximum volumetric energy density of 0.446 mW h cm?3 at a current density of 0.5 mA cm?2 and a maximum power density of 44.1 mW cm?3 at a current density of 6.0 mA cm?2 are achieved by the as‐assembled device. What's more, the device also shows excellent mechanical flexibility and little capacitance change after over 5000 charge/discharge cycles at a current density of 0.5 mA cm?2.  相似文献   

18.
The calculated and experimental Raman spectra of the (EMI+)TFSI ionic liquid, where EMI+ is the 1‐ethyl‐3‐methylimidazolium cation and TFSI the bis(trifluoromethanesulfonyl)imide anion, have been investigated for a better understanding of the EMI+ and TFSI conformational isomerism as a function of temperature. Characteristic Raman lines of the planar (p) and non‐planar (np) EMI+ conformers are identified using the reference (EMI+)Br salt. The anion conformer of C2 symmetry is confirmed to be more stable than the cis (C1) one by 4.5 ± 0.2 kJ mol−1. At room temperature, the population of trans (C2) anions and np cations is 75 ± 2% and 87 ± 4%, respectively. Fast cooling quenches a metastable glassy phase composed of mainly C2 anion conformers and p cation conformers, whereas slow cooling gives a crystalline phase composed of C1 anion conformers and of np cation conformers. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

19.
The effect of acidity upon the rate of nitrosation of N‐benzyl,O‐methylhydroxylamine ( 3 ) in 1:1 (v/v) H2O/MeOH at 25 °C has been investigated. The pseudo‐first‐order rate constant (kobs) for loss of HNO2 as the limiting reagent decreases as [H3O+] increases. This is compatible with two parallel reaction channels (Scheme 2 ). One involves the direct reaction of the free hydroxylamine with HNO2 (k1 = 1.4 × 102 dm3 mol?1 s?1, 25 °C) and the other involves the reaction of the free hydroxylamine with NO+ (k2 = 5.9 × 109 dm3 mol?1 s?1). In contrast, there is only a very slight increase in kobs with increasing [H3O+] for nitrosation of N,O‐dimethylhydroxylamine ( 4 ) in dilute aqueous solution at 25 °C to give N‐nitroso‐dimethylhydroxylamine, 5 . This also fits a two‐channel mechanism (Scheme 3 ). Again, one involves the nitrosation of the free base by NO+ (k2 = 8 × 109 dm3 mol?1 s?1, 25 °C) but the other channel now involves catalysis by chloride (k3 = 1.3 × 108 dm3 mol?1 s?1). Arising from these results, we propose an estimate of pKa ~ ?5 for protonated nitrous acid, (O = N? OH), which is appreciably different from the literature value of +1.7. The interconversion of cis and trans conformational isomers of 5 has been investigated by temperature‐dependent NMR spectroscopy in CDCl3, methanol‐d4, toluene‐d8 and dimethyl sulfoxide‐d6. Enthalpies and entropies of reaction and of activation have been determined and compared with computational values obtained at the B3LYP/6‐31G* level of theory. The cis form is slightly more stable at normal temperatures and no solvent effects upon the thermodynamics or kinetics of the conformational equilibrium were predicted computationally or detected experimentally. In addition, key geometric parameters and dipole moments have been calculated for the cis and trans forms, and for the lowest energy transition structure for their interconversion, in the gas phase and in chloroform. These results indicate electronic delocalisation in the ground states of 5 which is lost in the transition structure for their interconversion. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

20.
In this work, the experimental and theoretical vibrational spectra of N1‐methyl‐2‐chloroaniline (C7H8NCl) were studied. FT‐IR and FT‐Raman spectra of the title molecule in the liquid phase were recorded in the region 4000–400 cm?1 and 3500–50 cm?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method (B3LYP) with the 6‐311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT‐IR and FT‐Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. 13C and 1H NMR chemical shifts results were compared with the experimental values. The optimized geometric parameters (bond lengths and bond angles) were given and are in agreement with the corresponding experimental values of aniline and p‐methyl aniline. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

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