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71.
Quinoline formation via a modified Combes reaction: examination of kinetics,substituent effects,and mechanistic pathways 总被引:1,自引:0,他引:1
Joseph C. Sloop 《Journal of Physical Organic Chemistry》2009,22(2):110-117
This is the first reported investigation of the Combes condensation employing 19F NMR spectroscopy to monitor intermediate consumption and product formation rates. The reaction was found to be first order in both the diketone and aniline. Product regioselectivity and reaction rates were found to be influenced by substituents on the diketones and anilines with rates varying as much as five fold. The consumption rate of key imine and enamine intermediates mirrored quinoline formation rates, in accord with rate determining annulation. A ρ of ?0.32 was determined for this cyclization. While the sign of the reaction constant is consistent with rate limiting electrophilic aromatic substitution (EAS), the magnitude is likely a composite value, resulting from opposing substituent effects in the nucleophilic addition and EAS steps. Mechanistic details and reaction pathways supporting these findings are proposed. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
72.
Anilinolysis of O‐butyl phenyl phosphonochloridothioate in acetonitrile: Synthesis,characterization, kinetic study,and reaction mechanism 下载免费PDF全文
This paper describes a simple optimized method for the synthesis of O‐butyl phenyl phosphonochloridothioate ( 4 ) under mild conditions. The target compounds were characterized by 1H‐nuclear magnetic resonance (NMR), 13C‐NMR, and 31P‐NMR spectroscopy, as well as mass spectroscopy. The apparent structure of 4 was confirmed by optimization using the B3LYP/6‐311 + G(d,p) level in the Gaussian 09 program in acetonitrile. The nucleophilic substitution reactions of 4 with X‐anilines (XC6H4NH2) and deuterated X‐anilines (XC6H4ND2) were investigated kinetically in acetonitrile at 55.0°C. The free energy relationship with X in the anilines looked biphasic concave upwards with a break region between X = H and X = 3‐MeO, giving large negative ρX and small positive βX values. The deuterium kinetic isotope effects were secondary inverse (kH/kD < 1: 0.789‐0.995) and the magnitudes, (kH/kD), increased when the nucleophiles were changed from weakly basic to strongly basic anilines. A concerted SN2 mechanism is proposed on the basis of the selectivity parameters and the variation trend of the deuterium kinetic isotope effects with X. 相似文献
73.
Lu‐Feng Zou Kuang Shen Yao Fu Qing‐Xiang Guo 《Journal of Physical Organic Chemistry》2007,20(10):754-763
Experimental studies showed that sulfur radicals play the vital role in petroleum formation. 1 Sulfur‐ centered radicals also exhibit activities in antioxidant functions. Here we conduct a theoretical investigation of their precursor‐disulfides. By investigation into substituent effect on sulfur? sulfur bond dissociation enthalpies (S? S BDEs), we would like to find the most effective provider for sulfur radicals. In the present work, 50 alpha‐substituted disulfides and 16 para‐substituted aryl disulfides are studied systematically, with the general formula XS‐SX or HS‐SX. The substituent effect on S? S BDEs is found to be very eminent, ranging from 33.2 to 75.0 kcal/mol for alpha‐substituted disulfide, and from 43.7 to 59.7 kcal/mol for para‐substituted phenyl disulfides. We also evaluate the performance of 44 density functional methods to get an accurate prediction. A further study indicates that substituents play a major role in radical energies, instead of molecule energies, which is substantiated by the good linearity between XS‐SX bond dissociation enthalpy (BDE) and HS‐SX BDE. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
74.
The renewal of the urban waterfronts has become a major focus of attention for politicians and decision makers in the city’s management programs. The recognition of the patterns that define the waterfronts’ identity is essential to select new strategies of intervention for the environmental recovery. In order to create adequate environments for everyday life within a sustainable development, new links between human senses, human perception and design need to be created. Within this wide approach, the landscape and the soundscape play a significant role and can become a key driving force in the implementation of the changes. New techniques have to be tested to identify the sonic and visual parameters capable to explain the specificity of a waterfront. With this purpose, an artificial neural network (ANN) was developed, and the relative importance of the input variables was evaluated. The collected database was also analysed by multiple linear regression (MLR) to compare the outcomes of both models. The urban waterfront of Naples (Italy) was chosen as case study. The results obtained show that the performance of the neural network is better than the one of the linear regression (rANN = 0.949, rMLR = 0.639). The interpretation of the relative importance method is also quite satisfactory in the ANN. 相似文献
75.
F. Kastenholz E. Grell J. W. Bats G. Quinkert K. Brand H. Lanig F. W. Schneider 《Journal of fluorescence》1994,4(3):243-246
Two newly synthesized cryptands act as sensitive Na+- and K+-selective indicators for cation concentrations above 20 M. The fluorescence properties change markedly upon cation binding. In addition, the free ligands exhibit a pronounced sensitivity to pH, which is considerably lower for the cation complexes. Time resolved fluorescence is characterized by a decay time of about 5 ns that is attributed to the diprotonated protolytic state of the uncomplexed ligands. Semiempirical calculations show the systematic influence of the nitrogen lone pairs or the N–H bond on the stability of the system. The cause of the strong fluorescence intensity increase observed upon protonation of the fluorescent cryptands may be attributed to an increase in the S1–T
x
energy gap as a consequence of bridgehead nitrogen protonation.This is a peer-reviewed conference proceeding article from the Third Conference on Methods and Applications of Fluorescence Spectroscopy, Prague, Czech Republic, October 18–21, 1993. 相似文献
76.
G. Ruder 《Isotopes in environmental and health studies》2013,49(1-2):14-16
Seit nahezu 10 Jahren warden vom VEB Robotron Meβelektronik “Otto Schön” Dresden kontinuierliche Füllstandsmeβeinrichtungen hergestellt. Sie arbeiten nach dem Prinzip der Strahlenstreuung im Füllgut. Quelle und Strahlungsdetektor befinden sich — durch einen Absorber getrennt — in einer gemeinsamen Sonde. Die Sonde wird durch einen Motorantrieb dem jeweiligen Füllstand nachgeführt. Diese Messung wird bei Behälterhöhen bis maximal 40 m eingesetzt. In den Behälter ist der Einbau eines Schutzrohres für die Sonde erforderlich. Da strahlungsquelle und Detektor in einer gemeinsamen Sonde untergebracht sind, wird keine groβe Quellenaktivität benötigt. Die beschriebene neue Entwicklung ersetzt ab 2. Halbjahr 1982 den mit einigen Nachteilen behafteten Vorläufer dieser Füllstandsmeβanlage. Durch die vorgenommenen Verbesserungen warden der Inbetriebnahme- und der Wartungsaufwand verringert und die Zuverlässigkeit erhöbt. 相似文献
77.
78.
针对卫星导航信号模拟器的性能指标测试评估问题,提出了基于软件接收机的性能指标测试方法;通过分析模拟器性能,包括对动态性能、相位噪声、通道间时延一致性和静态定位精度的综合分析,给出了相应的测试方法和测试流程,并结合卫星导航信号模拟器产生的实际信号对各项性能指标的测试结果进行分析;经测试结果表明,软件接收机可以有效地对卫星导航信号模拟器各项性能指标进行测试,测试结果符合理论预期,满足模拟器性能指标测试评估的需求。 相似文献
79.
示波中和滴定指示剂的研究(Ⅲ) 总被引:3,自引:0,他引:3
本文介绍了对酸性示波中和指示剂刚果红、百里酚兰和对、间、邻-硝基酚等指示滴定终点时切口随变化的原理的探讨。 相似文献
80.
Nathan W. Fenwick Richard Telford Amie Saidykhan William H. C. Martin Richard D. Bowen 《Molecules (Basel, Switzerland)》2021,26(16)
The accelerated formation of 2,3-diphenylquinoxalines in microdroplets generated in a nebulizer has been investigated by competition experiments in which equimolar quantities of 1,2-phenylenediamine, C6H4(NH2)2, and a 4-substituted homologue, XC6H3(NH2)2 [X = F, Cl, Br, CH3, CH3O, CO2CH3, CF3, CN or NO2], or a 4,5-disubstituted homologue, X2C6H2(NH2)2 [X = F, Cl, Br, or CH3], compete to condense with benzil, (C6H5CO)2. Electron-donating substituents (X = CH3 and CH3O) accelerate the reaction; in contrast, electron-attracting substituents (X = F, Cl, Br and particularly CO2CH3, CN, CF3 and NO2) retard it. A structure–reactivity relationship in the form of a Hammett correlation has been found by analyzing the ratio of 2,3-diphenylquinoxaline and the corresponding substituted-2,3-diphenylquinoxaline, giving a ρ value of −0.96, thus confirming that the electron density in the aromatic ring of the phenylenediamine component is reduced in the rate-limiting step in this accelerated condensation. This correlation shows that the phenylenediamine acts as a nucleophile in the reaction. 相似文献