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1.
The specific rates of solvolysis of methanesulfonic anhydride have been measured conductometrically at ?10 °C in 41 solvents. Use of the extended Grunwald–Winstein equation, with the NT scale of solvent nucleophilicity and the YOTs scale of solvent ionizing power, leads to sensitivity to changes in solvent nucleophilicity (? value) of 0.95 and a sensitivity to changes in solvent ionizing power (m value) of 0.61, with a multiple correlation coefficient (R) of 0.973. Product selectivity values (S) in binary hydroxylic solvents favor alcohol attack in EtOH–H2O (a value of 1.2 in 90% EtOH rising to 4.0 in 40% EtOH) and in MeOH–H2O (a value of 3.7 in 90% MeOH rising to 6.0 in 50% MeOH). In 2,2,2,‐trifluoroethanol–H2O, the S values are much lower at about 0.1. Entropy of activation values are appreciably negative. Literature values for the specific rates of solvolysis of methanesulfonyl chloride have been extended to fluoroalcohol‐containing solvents (titrimetric method) and, at 45.0 °C, for an overall 43 solvents values are obtained (using NT and YC1 scales) of 1.20 for ? and of 0.52 for m (R = 0.969). It is proposed that both substrates solvolyze by an SN2 pathway. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

2.
A simple linear regression (Q equation) is devised to position solvolyses within the established SN2‐SN1 spectrum of solvolysis mechanisms. Using 2‐adamantyl tosylate as the SN1 model and methyl tosylate as the SN2 model, the equation is applied to solvolyses of ethyl, allyl, secondary alkyl and a range of substituted benzyl and benzoyl tosylates. Using 1‐adamantyl chloride as the SN1 model and methyl tosylate as the SN2 model, the equation is applied to solvolyses of substituted benzoyl chlorides in weakly nucleophilic media. In some instances, direct correlations with methyl tosylate were employed. Grunwald–Winstein l values and kinetic solvent isotope effects are also used to locate solvolyses within the spectrum of mechanisms. Product selectivities (S) for solvolyses at 50 °C of p‐nitrobenzyl tosylate in binary mixtures of alcohol–water and of alcohol–ethanol for five alcohols (methanol, ethanol, 1‐propanol and 2‐propanol and t‐butanol) are reported and show the expected order of solvent nucleophilicity (RCH2OH > R2CHOH > R3COH). The data support the original assignments establishing the NOTs scale of solvent nucleophilicity. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

3.
Modifications of the Swain–Scott equation (log k/k0) = sn) give an equation log k1 = (E + sN1′); k1 is the rate constant, E is an electrophilicity parameter, N1′ is a solvent nucleophilicity parameter and s is an electrophile‐specific sensitivity parameter. The equation is tested using over 300 published first‐order rate constants (k1) for decay of a range of benzhydrylium cations in various solvents, on which the published N1 scale of solvent nucleophilicity is based (S. Minegishi, S. Kobayashi and H. Mayr, J. Am. Chem. Soc. 2004, 126, 5174–5181) using the alternative equation log k = s(E + N1), in which s is a nucleophile‐specific parameter. The modified (E + sN1′) equation provides a revised N1′ scale of solvent nucleophilicity, and a more precise fit, with less than half the number of adjustable parameters. It is found that the sensitivities of the benzhydrylium cations to changes in solvent nucleophilicity decrease slightly as reactivity increases, in contrast to s(E + N) equations, which show no trends in s values. It is proposed that more reliable N scales can be defined using (E + sN), because N is determined directly from definitions, and residual errors (e.g. experimental or due to solvation effects) can be incorporated into the slope and intercept. The complex reasons for the success of equations of the type log k = s(E + N) are discussed. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

4.
In order to investigate the influence of solvent polarity on the rate effect of double bonds in reactions that proceed via an extended π‐participation mechanism, the solvolysis rates (kU) of the benzyl chloride derivative 1 and tertiary chloride 2 that have doubly unsaturated side chains were measured in absolute ethanol, 80% v/v. aq. ethanol and 97% wt. aq. trifluoroethanol. The rates of the corresponding saturated analogs 1S and 2S (kS) were measured in 80% aq. ethanol and 97% wt. aq. trifluoroethanol, while those in pure ethanol were calculated according to LFER equation log k = sf (Ef + Nf). In solvents with moderate ionizing power (ethanol and 80% aq. ethanol) the expected rate effects were obtained (kU/kS>1), while in solvent with high ionizing power (2,2,2‐trifluoroethanol) absence of the rate effect was observed (kU/kS≈1), indicating that in the kS process the solvation of the transition state is very important, while in kΔ process the breaking of the C? Cl bond is not appreciably developed in the transition state and the solvent effect is marginal. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

5.
The reactions of O‐(4‐methylphenyl) S‐(4‐nitrophenyl), O‐(4‐chlorophenyl) (4‐nitrophenyl), O‐(4‐chlorophenyl) S‐phenyl, and O‐(4‐methylphenyl) S‐phenyl dithiocarbonates ( 1 , 2 , 3 , and 4 , respectively) with a series of secondary alicyclic (SA) amines are subjected to a kinetic investigation in 44 wt% ethanol‐water, at 25.0 °C and an ionic strength of 0.2 M. The reactions are followed spectrophotometrically. Under amine excess, pseudo‐first‐order rate coefficients (kobs) are found. For some of the reactions, plots of kobs vs. free amine concentration at constant pH are linear but others are nonlinear upwards. This kinetic behavior is in accordance with a stepwise mechanism with two tetrahedral intermediates, one zwitterionic (T±) and the other anionic (T?). In some cases, there is a kinetically significant proton transfer from T± to an amine to yield T?. Values of the rate micro constants k1 (amine attack to form T±), k?1 (its back step), k2 (nucleofuge expulsion from T±), and k3 (proton transfer from T± to the amine) are determined for some reactions. The Brønsted plots for k1 are linear with slopes β1 = 0.2–0.4 in accordance with the slope values found when T± formation is the rate‐determining step. The sensitivity of log k1 and log k?1 to the pKa of the amine, leaving and non‐leaving groups are determined by a multiparametric equation. For the reactions of 1 – 4 with 1‐formylpiperazine and those of 3 and 4 with morpholine the k2 and k3 steps are rate determining. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

6.
The second‐order rate constants k (dm3mol?1s?1) for alkaline hydrolysis of meta‐, para‐ and ortho‐substituted phenyl esters of benzoic acid, C6H5CO2C6H4‐X, in aqueous 50.9% (v/v) acetonitrile have been measured spectrophotometrically at 25 °C. In substituted phenyl benzoates, C6H5CO2C6H4‐X, the substituent effects log kX ? log kH in aqueous 50.9% acetonitrile at 25 °C for para, meta and ortho derivatives showed good correlations with the Taft and Charton equations, respectively. Using the log k values for various media at 25 °C, the variation of the ortho substituent effect with solvent was found to be precisely described with the following equation: Δlog kortho = log kortho ? log kH = 1.57σI + 0.93σ°R + 1.08EsB ? 0.030ΔEσI ? 0.069ΔEσ°R, where ΔE is the solvent electrophilicity, ΔE = ES ? EH20, characterizing the hydrogen‐bond donating power of the solvent. We found that the experimental log k values for ortho‐, para‐ and meta‐substituted phenyl benzoates in aqueous 50.9% acetonitrile at 25 °C, determined in the present work, precisely coincided with the log k values predicted with the equation (log kX)calc = (log kHAN)exp + (Δlog kX)calc where the substituent effect (Δlog kX)calc was calculated from equation describing the variation of the substituent effect with the solvent electrophilicity parameter, using for aqueous 50.9% CH3CN the solvent electrophilicity parameter, ΔE = ?5.84. In going from water to aqueous 50.9% CH3CN, the ortho inductive term grows twice less as compared with the para polar effect. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

7.
A limited series of 4eq‐substituted (X) 2‐methyleneadamantanes ( 6 , Y?CH2, X?F, Cl, Br, I, and SnMe3) has been synthesized and diastereoselectivities for their hydrochlorination (HCl/CH2Cl2) have been determined. Diastereoselectivities for the fluorination (DAST/CH2Cl2) of secondary alcohol mixtures, obtained from the hydride reduction of the precursor ketones ( 6 ,Y?O) to the alkenes, have also been measured. A comparison of this selectivity data for nucleophilic trapping of 4eq‐substituted (X) 2‐adamantyl cations ( 4 , R?H and Me) with the corresponding information for 5‐substituted (X) 2‐adamantyl cations ( 1 , R?H and Me) has revealed important distinctions between the two series. In particular, whereas extended hyperconjugative effects appear to be the predominant electronic effect governing facial selectivity in the 5,2‐series, electrostatic influences prevail in the 4,2‐disposition. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

8.
Friedel–Crafts acylation and alkylation reactions were investigated using density functional theory calculations. The reaction systems studied were (benzene + acetyl chloride + Al2Cl6 (or AlCl3)) and (benzene + 2‐chloropropane + Al2Cl6). In the acylation reaction, the acylium ion intermediate is reached either via a Me? C(Cl)?O? Al2Cl6 complex or via direct Cl transfer: Me? C(?O)Cl? Al2Cl6 → Me? C?O?+? Al2Cl. The ion adds to benzene electrophilically to form a Wheland intermediate containing a strong C? H? Cl hydrogen bond, which leads to deprotonation and the subsequent formation of acetophenone. The resulting H? Cl? Al2Cl6 fragment is subjected to a nucleophilic attack by the carbonyl oxygen of the acetophenone, and recovery of the Al2Cl6 bridge is unlikely. Attack of the Al2Cl6 moiety by Me? C(Cl)?O gives the complex Me? C(Cl)?O–AlCl3, whose reactivity toward acylation is similar to that of the Me? C(Cl)?O–Al2Cl6 complex. In the alkylation reaction, deprotonation does not take place, but rather a [1,2] H‐shift from the Wheland intermediate. The resulting α‐protonated cumene undergoes deprotonation, with subsequent recovery of the Al2Cl6 bridge. In addition, the Al2Cl6‐catalyzed isomerization of the n‐propyl to the isopropyl cation was found to be a dyotropic shift. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

9.
Rate constants are reported for the reactions of 1‐phenoxy‐dinitrobenzenes, 3 , 1‐phenoxy‐dinitrotrifluoromethylbenzenes, 4 , with n‐propylamine, and 1‐methylheptylamine in acetonitrile as solvent. The results are compared with results reported previously for n‐butylamine, pyrrolidine, and piperidine. Decreasing ring activation leads to lower values of k1 for nucleophilic attack although this may be mediated by reduced steric congestion around the reaction centre. Specific steric effects, leading to rate retardation, are noted for the ortho‐CF3 group. In general, reactant‐bearing ortho‐CF3 group were subject to base catalysis irrespective of the amine nucleophile and values of kAm/k?1 are reduced as the size of the amine get bulkier. This is likely to reflect increases in values of k?1 coupled with decreases in values of kAm as the proton transfer from zwitterionic intermediates to catalysing amine becomes less thermodynamically favourable.  相似文献   

10.
The reaction mechanisms as well as substituted effect and solvent effect of the enyne–allenes are investigated by Density Functional Theory (DFT) method and compared with the Myers–Saito and Schmittel reactions. The Myers–Saito reaction of non‐substituted enyne–allenes is kinetically and thermodynamically favored as compared to the Schmittel reaction; while the concerted [4 + 2] cycloaddition is only 1.32 kcal/mol higher than the C2? C7 cyclization and more exothermic (ΔRE = ?69.38 kcal/mol). For R1 = CH3 and t‐Bu, the increasing barrier of the C2? C7 cyclization is higher than that for the C2? C6 cyclization because of the steric effect, so the increased barrier of the [4 + 2] cycloaddition is affected by such substituted electron‐releasing group. Moreover, the strong steric effect of R1 = t‐Bu would shift the C2? C7 cyclization to the [4 + 2] cycloaddition. On the other hand, for R1 = Ph, NH2, O?, NO2, and CN substituents, the barrier of the C2? C6 cyclization would be more diminished than the C2? C7 cyclization due to strong mesomeric effect; the reaction path of C2? C7 cyclization would also shift to the [4 + 2] cycloaddition. The solvation does not lead to significant changes in the potential‐energy surface of the reaction except for the more polar surrounding solvent such as dimethyl sulfoxide (DMSO), or water. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

11.
Polymeric micelles are attractive nanocarriers for hydrophobic drug molecules such as the kinase inhibitor dactolisib. Two different poly(ethylene glycol)–poly(acrylic acid) (PEG‐b‐PAA) block‐copolymers are synthesized, PEG(5400)‐b‐PAA(2000) and PEG(10000)‐b‐PAA(3700), respectively. Polymeric micelles are formed by self‐assembly once dactolisib is conjugated via the ethylenediamine platinum(II) linker (Lx) to the PAA block of the block copolymers. Dactolisib micelles with dactolisib loading content of 17% w/w show good colloidal stability and display sustained release of Lx‐dactolisib over 96 h in PBS at 37 °C, while media containing reagents that compete for platinum coordination (e.g., glutathione (GSH) or dithiothreitol (DTT)) effectuate release of the parent inhibitor dactolisib at similar release rates. Dactolisib/lissamine‐loaded micelles are internalized by human breast adenocarcinoma cells (MCF‐7) in a dose and time‐dependent manner as demonstrated by confocal microscopy. Dactolisib‐loaded micelles inhibit the PI3K/mTOR signaling pathway at low concentrations (400 × 10?9 m ) and exhibit potent cytotoxicity against MCF‐7 cells with IC50 values of 462 ± 46 and 755 ± 75 × 10?9 m for micelles with either short or longer PEG‐b‐PAA block lengths. In conclusion, dactolisib loaded PEG‐b‐PAA micelles are successfully prepared and hold potential for nanomedicine‐based tumor delivery of dactolisib.  相似文献   

12.
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   

13.
The reactions of O‐(4‐methylphenyl) S‐(4‐nitrophenyl) dithiocarbonate and O‐(4‐chlorophenyl) S‐(4‐nitrophenyl) dithiocarbonate with a series of anilines are subjected to a kinetic investigation in 44 wt% ethanol–water, at 25.0 °C and an ionic strength of 0.2 M. The reactions are followed spectrophotometrically at 420 nm (appearance of 4‐nitrobenzenethiolate anion). Under excess amine, pseudo‐first‐order rate coefficients (kobs) are found. For the reactions of both substrates with anilines, plots of kobs versus free amine concentration at constant pH are nonlinear upwards, according to a second‐order polynomial equation. This kinetic behavior is in agreement with a stepwise mechanism consisting of two tetrahedral intermediates, one zwitterionic (T±) and the other anionic (T?), with a kinetically significant proton transfer from T± to an aniline to yield T?. The rate equation was derived from the proposed mechanism. By nonlinear least‐squares fitting of the rate equation to the experimental data, values of the rate micro‐coefficients involved in both steps were determined. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

14.
Transesterification of a phosphodiester bond of RNA models has been studied in various buffer solutions, under neutral and slightly alkaline conditions in H2O and D2O. The results show that imidazole is the only buffer system where a clear buffer catalysis on the cleavage of a phosphodiester bond is observed. The rate enhancement in sulphonic acid buffers is smaller, and a sulphonate base, particularly, is inactive as a catalyst. The rate‐enhancing effect of imidazole is, however, catalytic, and the catalytic inactivity of sulphonate buffers can be attributed to their structure and/or charge. The catalysis by imidazole is a complex system which, in addition to first‐order reactions, involves a process that shows a second‐order dependence in imidazole concentration. The latter reaction becomes significant in acidic imidazole buffers (pH < pKa), as the buffer concentration increases. The kinetic solvent deuterium isotope effect kH/kD, referring to first‐order catalysis by imidazole base, is 2.3 ± 0.3. That referring to second‐order catalysis is most probably much larger, but an accurate value could not be obtained. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

15.
The reactions of quinuclidines with phenyl, 4‐chlorophenyl, 4‐cyanophenyl, and 4‐nitrophenyl chlorothionoformates ( 1 , 2 , 3 , and 4 , respectively) are subjected to a kinetic study in aqueous solution, at 25.0°C, and an ionic strength of 0.2 M (KCl). The reactions are studied by following spectrophotometrically the release of the corresponding phenoxide anion/phenol generated in the parallel hydrolysis of the substrates. Under amine excess, pseudo‐first‐order rate coefficients (kobs) are found. Plots of kobs versus [amine] are linear, with slope kN. The Brønsted‐type plots (log kN vs. pKa of aminium ions) are linear, with slopes β = 0.26, 0.22, 0.19, and 0.28 for the reactions with 1 , 2 , 3 , and 4 , respectively. The magnitudes of the slopes indicate that these mechanisms are stepwise, with rate‐determining formation of a zwitterionic tetrahedral intermediate (T±). A dual parametric equation with the pKa of the nucleophiles and non‐leaving groups show βN = 0.26 and β nlg = ?0.16, also in accordance with the proposed mechanism. On the other hand, the reactivity of these thiocarbonyl substrates and their carbonyl derivatives was studied using their hardness index and compared with their experimental parameters, confirming the proposed mechanisms. By comparison of the title reactions with similar aminolyses, the following conclusions arise: (i) The mechanism of the reactions under investigation is stepwise with rate‐determining formation of T±. (ii) The reactivity of the substrates toward quinuclidines follows the order 4 > 3 > 2 > 1 . (iii) Quinuclidines are more reactive than isobasic pyridines toward chlorothionoformates. (iv) Chlorothionoformates are less reactive than chloroformates towards quinuclidines in accordance with the HSAB principle. (v) The kN values for phenyl chloroformate and 4 can be correlated with the pKa of quinuclidines and also with the hardness values calculated by the HF/3‐21G level of theory. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

16.
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   

17.
The reaction of the substituted phenacyl bromides 1a–e and 2a–e with thioglycolic acid 3 and thiophenol 6 in methanol underwent nucleophilic substitution SN2 mechanism to give the corresponding 2‐sulfanylacetic acid derivatives 4a–e, 5a–e and benzenethiol derivatives 9a–e, 10a–e. The reactants and products were identified by mass spectra, infrared and nuclear magnetic resonance. We measured the kinetics of these reactions conductometrically in methanol at a range of temperatures. The rates of the reactions were found to fit the Hammett equation and correlated with σ‐Hammett values. The ρ values for thioglycolic acid were 1.22–1.21 in the case of 4‐substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.39–0.35. The ρ values for thiophenol were 0.97–0.83 in the case of 4‐substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.79–0.74. The Brønsted‐type plot was linear with a α = ?0.41 ± 0.03. The kinetic data and structure‐reactivity relationships indicate that the reaction of 1a–e and 2a–e with thiol nucleophiles proceeds by a concerted mechanism. The plot of log k45 versus log k30, the plot log(kx,3‐NO2/kH) versus log(kx/kH), and the Brønsted‐type correlation indicate that the reactions of the thiol nucleophiles with the substituted phenacyl bromides 1a–e and 2a–e are attributed to the electronic nature of the substituents. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

18.
To obtain direct evidence of the formation of the Ni–Mo–S phase on NiMo/Al2O3 catalysts under high‐pressure hydrodesulfurization conditions, a high‐pressure EXAFS chamber has been constructed and used to investigate the coordination structure of Ni and Mo species on the catalysts sulfided at high pressure. The high‐pressure chamber was designed to have a low dead volume and was equipped with polybenzimidazole X‐ray windows. Ni K‐edge k3χ(k) spectra with high signal‐to‐noise ratio were obtained using this high‐pressure chamber for the NiMo/Al2O3 catalyst sulfided at 613 K and 1.1 MPa over a wide k range (39.5–146 nm?1). The formation of Ni–Mo and Mo–Ni coordination shells was successfully proved by Ni and Mo K‐edge EXAFS measurement using this chamber. Interatomic distances of these coordination shells were almost identical to those calculated from Ni K‐edge EXAFS of NiMo/C catalysts sulfided at atmospheric pressure. These results support the hypothesis that the Ni–Mo–S phase is formed on the Al2O3‐supported NiMo catalyst sulfided under high‐pressure hydrodesulfurization conditions.  相似文献   

19.
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   

20.
Hydrogenated amorphous silicon (a‐Si:H) films were studied using infrared and Raman spectroscopy. We have experimentally found that ratios of Raman scattering cross‐sections for Si–H to Si–Si bonds and for Si–H2 to Si–Si bonds are equal to 0.65 ± 0.07 and 0.25 ± 0.03, respectively. It allows to measure the concentration of hydrogen in a‐Si:H films. The developed approach can be applied for in situ control of hydrogen in a‐Si:H films and also suitable for thin a‐Si:H films on substrates that are opaque in infrared spectral region. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

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