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1.
    
Electrochemical reduction and oxidation of a series of 1‐substituted naphthalenes (1‐X‐naphthalenes) have been studied by the method of cyclic voltammetry (CV). The first reduction peak of the majority of these compounds corresponds to a one‐electron transfer to form the relatively stable radical anion (RA). For these species, ESR spectra have been registered and interpreted, the life time has been estimated. The first oxidation peaks of 1‐X‐naphthalenes are irreversible and correspond to a transfer of two or more electrons. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

2.
    
ESR studies carried out during the reaction of ferrocenoylsilanes with Grignard reagents at low temperature led to the detection of the radical anions of the former compounds. Cyclic voltammetric experiments indicate that the observed radical anions are likely to originate through an inner‐sphere electron transfer process. Different radical species were observed upon annealing, originating from destruction of the ferrocenyl moiety. Paramagnetic species were also detected on reacting ferrocenoylsilanes with LiAlH4. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

3.
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Electrochemical reduction (ECR) and oxidation (ECO) of 5,6,7,8‐tetrafluoroquinoxaline ( 1 ) and its derivatives bearing various substituents R (7‐H ( 2 ), 7,8‐H2 (3 ), 6‐CF3 ( 4 ), 6‐Cl ( 5 ), 5,7‐Cl2 ( 6 ), 5‐NH2 ( 7 ), 6‐OCH3 ( 8 ), 6,7‐(OCH3)2 ( 9 ), 6,7,8‐(OCH3)3 ( 10 ), 5,6,7,8‐(OCH3)4 ( 11 ), 6‐OCH3,7‐N(CH3)2 ( 12 ), 6‐N(CH3)2 ( 13 ), 6,7‐(N(CH3)2)2 ( 14 ), 5,6,7‐(N(CH3)2)3 ( 15 ), and 7,8‐cyclo‐(=CF‐CF = CF‐CF=) ( 16 )) in the carbocycle have been studied by cyclic voltammetry in MeCN. For 1 – 4 and 7 – 15 , the first reduction peaks have been found to be 1‐electron and reversible, thus corresponding to the formation of their radical anions (RAs), which are long lived at 295 K except those of 4 – 6 and 15 , 16 . Irreversible hydrodechlorination has been observed for 5 and 6 at the first step of their ECR confirmed by EPR detection of corresponding RAs of 2 and 5,7‐H2 derivative of 1 ( 17 ) at the next steps. Electrochemically generated RAs of 1 – 3 , 7 – 14 , and 17 have been characterized in MeCN by EPR spectroscopy together with DFT calculations at the (U)B3LYP/6‐31 + G(d) level of theory using PCM to describe the solvent. A noticeable alternation of spin density on the –NCCN– moiety of quinoxaline has been observed for all RAs possessing R‐substitution asymmetry. The comparative electron‐accepting ability of 1 – 15 has been analyzed in terms of their experimental reduction peak potentials and the (U)B3LYP/6‐31 + G(d)‐calculated gas‐phase first adiabatic electron affinities (EAs). The differences in electron transfer solvation energies for 1 – 15 have been evaluated on the basis of ECR peaks' potentials and calculated gas‐phase EAs. The ECO of 1 – 5 and 7 – 14 has been found to be irreversible.  相似文献   

4.
    
The addition reactions of some amides and aromatic amines to a CN double bond of 3,4‐diphenyl‐1,2,5‐thiadiazole 1,1‐dioxide ( 1 ) were studied in aprotic solvent solutions [N,N‐dimethylformamide (DMF) and acetonitrile (MeCN)]. Equilibrium constants for the reactions of 1 with acetamide, 2‐fluoroacetamide, butyramide, benzamide, aniline and 3‐aminopyridine were measured using a previously reported cyclic voltammetric (CV) method. Aliphatic amines gave unstable solutions, probably owing to reactions of anionic species derived from 1 . Other N nucleophiles tested (formamide, succinimide, thioacetamide and cyanamide) yielded different products that have not yet been characterized. DMF, N,N‐dimethylacetamide (DMA) and N‐methylacetamide did not react. The addition thiadiazoline produced in the reaction of acetamide with 1 was characterized by IR and 1H and 13C RMN NMR spectroscopy as a prototype compound. For this system, the equilibrium constant could also be measured by a standard UV–VIS method and was found to be in agreement with the value obtained by CV. The reaction of 1 with urea produced a bicyclic product, identified as 3a,6a‐diphenyltetrahydroimidazo[4,5‐c]‐1,2,5‐thiadiazol‐5‐one 2,2‐dioxide. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

5.
    
The nucleophilic addition reactions of several alcohols and 1‐propanethiol to a CN double bond of 3,4‐disubstituted derivatives of 1,2,5‐thiadiazole 1,1‐dioxide were studied in acetonitrile solution. The substrates used were 3,4‐diphenyl ( 1a ), 3‐methyl‐4‐phenyl ( 1b ), phenanthro[9,10‐c] ( 1c ) and acenaphtho[1,2‐c]‐1,2,5‐thiadiazole 1,1‐dioxide ( 1d ), 3,4‐diphenyl‐1,2,5‐thiadiazoline 1,1‐dioxide ( 2a ) and 4‐ethoxy‐5‐methyl‐3,4‐diphenyl‐1,2,5‐thiadiazoline 1,1‐dioxide ( 2b ). Spectroscopically (UV–VIS) and electrochemically (cyclic voltammetry) measured equilibrium constants at 25.0 °C are presented and discussed for the reaction of 1a and 1b with alcohols (methanol, n‐propanol, n‐butanol, isobutanol, 2‐propanol, sec‐butanol , tert‐butanol, ethylene glycol, allyl alcohol and 2‐phenylethanol). A reaction of 1‐propanethiol with 1c was observed, but the alcohols did not react with 1c , 1d or the thiadiazolines ( 2a , 2b ). The effect of the solvent on the equilibrium constant of the 1a–ethanol system was measured using, besides acetonitrile, propylene carbonate, N,N‐dimethylformamide, N,N‐dimethylacetamide, dimethyl sulfoxide and tert‐butanol. The results were correlated with an empirical H‐bond acceptor solvent parameter. Previously unreported spectroscopic (UV–VIS, IR, 1H and 13C NMR) data for some of the compounds studied are also provided. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

6.
    
Electrochemical reduction of 2,4‐dimethyl(diethyl)‐9‐oxo‐10‐(4‐heptoxyphenyl)‐9H‐thioxanthenium hexafluorophosphates in acetonitrile (MeCN) and N,N‐dimethylformamide is an irreversible 1‐electron process accompanied by the cleavage of the C(Ph)‐S bond in thioxanthenium cations with the formation of the corresponding 2,4‐dimethyl(diethyl)‐9H‐thioxanthene‐9‐ones. One‐electron reversible electrochemical reduction of the latter compounds occurs at more negative potentials and yields the corresponding radical anions, which have been characterized by electron paramagnetic resonance spectroscopy and density functional theory calculations at the (U)B3LYP/6‐31+G*/polarizable continuum model level of theory.  相似文献   

7.
    
Radical anions of 3,4‐aryl disubstituted 1,2,5‐thiadiazole 1,1‐dioxide were obtained by chemical and electrochemical reduction of their substrates, and characterized by ESR spectroscopy and cyclic voltammetry. The radical anion of the phenanthro[9,10‐c]‐1,2,5‐thiadiazole 1,1‐dioxide was found to be very stable in an aprotic solvent solution and did not react readily when water was added to the aprotic solvent, or the solution was saturated with oxygen gas. The radical formation chemical reaction competed with nucleophilic addition to the C?N bond of the thiadiazoles. A possible reaction mechanism, and a common reaction intermediate, supported by density functional theory calculations, is presented for the most stable radical. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

8.
    
Spin–spin interactions were examined for bis(tetrathiafulvalenyl) (TTF) derivatives bridged with a 1,1‐vinyl group (2,2‐diphenyl, 1 : 2,2‐fluorenylidene, 2 ; and 2,2‐dimethyl, 3 ). The chemical oxidation of these cross‐conjugated TTFs using AgClO4 yielded characteristic seven‐line ESR spectra, indicating the exchange interactions between the unpaired electrons on each TTF moiety. Compounds 2 and 3 , in addition, exhibited fine structures and half‐field resonances in the frozen solutions, which evidence the triplet interaction in the solid state, even with a twisted geometry of the molecular configuration. These findings substantiate the possibility of spin–spin interactions or triplet ground states predicted for some TTF oligomers. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

9.
    
The bioreduction of N‐oxide compounds is the basis for the mode of action of a number of biologically active molecules. These compounds are thought to act by forming a reactive oxygen species through an intracellular reduction and subsequent redox cycling process within the organism. With these results in mind, the preliminary investigation into the electrochemical reduction of the benzisoxazole 2‐oxide ring system was undertaken, with the thought that this class of compounds would reduce in a similar fashion to other N‐oxide heterocycles. The electrochemical reduction of 3‐phenyl‐1,2‐benzisoxazole 2‐oxide on boron‐doped diamond was studied using cyclic and square wave voltammetry as well as controlled potential electrolysis and HPLC for qualitative identification of the reaction products. It was found that the reduction proceeded with an initial quasi‐reversible one‐electron reduction followed by the very fast cleavage of either the endocyclic or exocyclic N–O bond. Subsequent electron transfer and protonation resulted in an overall two‐electron reduction and formation of the 2‐hydroxyaryl oxime and benzisoxazole. These results are analogous to those observed in the electrochemical reduction of other heterocyclic N‐oxides albeit the reduction of the benzisoxazole N‐oxides takes place at a more negative potential. However, these encouraging results warrant further investigation into the reduction potential of substituted benzisoxazole N‐oxides as well as to elucidate and characterize the nature of the intermediate species involved. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

10.
    
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11.
    
In this wok, a uniform layer of La2O3 is coated on the surface of LiNi0.91Co0.06Mn0.03O2 Ni-rich cathode material by using a wet coating process. The XPS and EDX analysis confirms the presence of La2O3 coating on the surface of NCM. The coated samples deliver the superior electrochemical performance, 0.2 wt % La2O3 (LaO-0.2) NCM exhibits discharge capacity of 202.7 mAh g−1 in 1st cycle and delivered the cycle stability of 87.2% after 100 cycles. Besides, the enhanced capacity retention, LaO-0.2 has delivered very high discharge capacity of 80.3 mAh g−1 at very high C-rate of 5C while the pristine sample shows very low discharge capacity (33.4 mAh g−1). CV results shows the significant suppression in the intensity of H2–H3 which indicates the superior electrochemical stability of LaO-0.2 NCM. Thus, we can confirm that La2O3 coating is promising technique to achieve superior electrochemical performance in the long term cycling process.  相似文献   

12.
    
Ten nitrophenyl N‐glycosides have been studied electrochemically in neutral (at pH 7) water–organic solutions by cyclic voltammetry using static mercury drop electrode. For all compounds under investigation the two electrochemical processes have been observed: the four‐electron irreversible reduction of their nitro groups to the corresponding phenylhydroxylamine derivatives, as well as the two‐electron quasi‐reversible process between phenylhydroxylamine and nitroso derivatives. For three compounds the additional electrochemical processes have been also observed, which can be connected with the formation of azoxybenzene derivatives. The potentials of both redox processes: a two‐electron quasi‐reversible R? NHOH/R? NO (Ef) and four‐electron irreversible R? NO2/R? NHOH (Epc(I)) systems have been determined and discussed according to crystal structures of selected compounds. Ef and Epc(I) depended strongly on the positive mesomeric effect (caused by glycosidic nitrogen atom), as well as on the intramolecular hydrogen bond between electroactive nitro group and the hydrogen atom at the glycosidic atom observed in N‐o‐nitrophenyl‐2,3,4,6‐tetra‐O‐acetyl‐β‐D ‐glucopyranosylamine. Moreover, the chirality of selected reactants has had the pronounced effect on the Epc(I). Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

13.
    
The effect of the non‐electroactive groups on the redox potentials of the active centres of 26 nitrophenyl O‐glycosides possessing various substituents has been studied electrochemically using cyclic voltammetry. The potentials of both redox processes, a two‐electron quasi‐reversible R‐NHOH/R‐NO (Ef) and four‐electron irreversible R‐NO2/R‐NHOH (Epc(I)) systems, have been determined and compared for all the compounds under investigations. The nitrophenyl O‐glycosides were chosen as model compounds as they significantly vary in many aspects of their structure such as: (i) the isomeric substitution of nitro group in benzene ring to the sugar moiety (ortho, meta and para isomers); (ii) the size of sugar moieties (the derivatives of mono‐ and disaccharides); (iii) the presence and absence of additional groups in saccharidic fragments (e.g. pentose and hexose); (iv) functionalisation of hydroxyl groups (free or acetylated hydroxyl groups) and (v) absolute configurations of selected sugar carbon atoms (e.g. the pairs of anomers). Among other effects, a significant variation in the increasing order of the two‐electron quasi‐reversible (Ef, ortho > meta > para) and four‐electron irreversible (Epc(I), meta > ortho > para) redox processes has been found and explained taking into account the negative inductive effect (–I) caused by the glycosidic oxygen atom that facilitates the electroreduction of the nitro group, and the positive mesomeric effect (+M) which makes the electroreduction more difficult. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

14.
    
In comparison with 2,1,3‐benzothia(selena)diazoles, electrochemical oxidation and reduction of their 4,5,6,7‐tetrafluoro derivatives and a number of related compounds were studied by cyclic voltammetry. For nine examples of this class, the first reduction peaks are reversible and corresponding radical anions (RAs) are long‐lived at 295 K in MeCN and especially in DMF. The oxidation peaks were irreversible and corresponding radical cations were not observed. Electrochemically generated RAs were characterized by EPR measurements and DFT calculations at the UB3LYP/6‐31+G(d) level. The spin density distribution in the RAs is analyzed in connection with effects of S substitution by Se and/or H by F. The prospects of the studied RAs in the design and synthesis of magnetically active materials are discussed. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

15.
石型 《波谱学杂志》1996,13(6):509-518
我们将微波电子自族共振仪的吸收谐振腔为光化学反应器.在其各种流体及温度的范围内讨论其光化学效应.作者所用的模型乃是有机烷基-亚硝酸类在醇类的动力研究,许多不同的双氢氧烷基及烷氧基-烷基与一氧化氮所结合的自由基均由光分解而产生不同的电子自旋共振光谱.最有兴趣的是产生对映结构的双氢氧乙烷基与一氧化氮所结合的异构物自由基,它们的几何形态可用分子振动理论及共价键理论来解析.自标准化学键长及化学键角度,这些烷氧基-烷基与一氧化氛所结合的自由基还存在很强的氢键,这些将会在科学上,如生物化学、生物学及医学上的氧化及还原反应有相当重要的位置.  相似文献   

16.
The reaction channels of di‐tert‐butylcarbene ( 2 ), its radical anion, ( 3 ) and its radical cation ( 4 ) were investigated theoretically by using DFT/B3LYP with 6‐31+G(d) basis set and 6‐311+G(2d,p) for single point energy calculations. Conversion of the neutral carbene 2 to the charged species 3 and 4 results in significant geometric changes. In cation 4 two different types of C (CH3)3 bonds are observed: one elongated sigma bond called “axial” with 1.61 Å and two normal sigma bonds with a bond length of 1.55 Å. Species 2 and 4 have an electron deficient carbon center; therefore, migration of CH3 and H is observed from adjacent tert‐butyl groups with low activation energies in the range of 6–9 kcal/mol like similar Wagner–Meerwein rearrangements in the neopentyl‐cation system. Neutral carbene 2 shows C H insertion to give a cyclopropane derivative with an activation energy of 6.1 kcal/mol in agreement with former calculations. Contrary to species 2 and 4 , the radical anion 3 has an electron rich carbon center which results in much higher calculated activation energies of 26.3 and 42.1 kcal/mol for H and CH3 migrations, respectively. NBO charge distribution indicates that the hydrogen migrates as a proton. The central issue of this work is the question: how can tetra‐tert‐butylethylene ( 1 ) be prepared from reaction of either species 2 , 3 , or 4 as precursors? The ion–ion reaction between 3 and 4 to give alkene 1 with a calculated reaction enthalpy of 203.5 kcal/mol is extremely exothermic. This high energy decomposes alkene 1 after its formation into two molecules of carbene 2 spontaneously. Ion–molecule reaction of radical anion 3 with the neutral carbene 2 is a much better choice: via a proper oriented charge–transfer complex the radical anion of tetra‐tert‐butylethylene (11) is formed. The electron affinity of 1 was calculated to be negligible. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

17.
用循环伏安法与现场ＥＳＲ方法结合，研究了６－硝基喹啉在ＤＭＳＯ介质中，Ｐｔ电极上的电化学行为，检测到了电化学还原的中间产物阴离子自由基，估算了阴离子自由基衰变的速度常数，提出了６－硝基喹啉电化学还原的机理。  相似文献   

18.
    
The reactions of several derivatives of 1,2,5‐thiadiazole 1,1‐dioxide [3,4‐diphenyl‐( 1a ), 3,4‐bis(p‐methoxyphenyl)‐( 1b ), phenanthro[9,10‐c]‐( 1c ) and acenaphtho[1,2‐c]‐1,2,5‐thiadiazole 1,1‐dioxide ( 1d ), 3,4‐diphenyl‐1,2,5‐thiadiazoline 1,1‐dioxide ( 2a ) and 4‐ethoxy‐5‐methyl‐3,4‐diphenyl‐1,2,5‐thiadiazoline 1,1‐dioxide ( 2b )], with reagents possessing two nucleophilic nitrogen atoms (urea, N,N′‐dimethylurea, thiourea, N‐methylthiourea, N‐ethylthiourea, N‐allylthiourea, N,N′‐diethylthiourea, N,N′‐diphenylthiourea, dithioxamide and sulfamide), were followed by cyclic voltammetry (CV) and UV–visible spectrophotometry in aprotic solvent solution. The products were isolated, characterized by IR, 1H NMR and 13C NMR methods and their structure was confirmed by single‐crystal x‐ray diffraction. Several substrate–nucleophile combinations ( 1a – d and 2a with some ureas and thioureas) reacted to give good yields of new compounds formed by the addition reaction of the two nitrogen atoms of the nucleophile to the two >CN— double bonds of the 1,2,5‐thiadiazole 1,1‐dioxide ring. Some systems ( 1a –dithioxamide and 2b –thiourea) did not react, whereas in others (e.g. 1a –sulfamide) a monoaddition equilibrium reaction was observed. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

19.
杨正红  王夔 《波谱学杂志》1992,9(2):165-170
利用电子自旋共振方法对固体胆红素及其自由基在紫外照射下的变化进行了研究,发现在紫外光下仅引起胆红素超氧自由基及半醌自由基浓度的增加,而没有新的自由基形式生成,指出Foote提出的光氧化机理假说的中间体自由基即是由上述两种自由基构成,并通过电子计算机对ESR谱的摸拟,提出了紫外辐照下的胆红素自由基形成机理,推测胆红素光化学反应的途径及产物与这两种自由基浓度及在不同环境下的反应活性有关.  相似文献   

20.
    
Reactivity of two new C4‐indolyl substituted 1,4‐dihydropyridines (1,4‐DHPs) toward superoxide anion (O2? ) in dimethylsulfoxide (DMSO) is reported. Reactivity was followed by electrochemical and spectroscopic techniques. Gas chromatography‐mass spectrometry (GC–MS) was used to identify the final products of the reaction. C4 indolyl‐substituted‐1,4‐DHPs reacted toward O2? at significant rates, according to the calculated kinetic rate constants. Results are compared with 4‐phenyl‐DHP and the commercial 1,4‐DHPs, nimodipine, nisoldipine, and amlodipine. Indolyl‐substituted 1,4‐DHPs were more reactive than the commercial derivatives. The direct participation of proton of the 1‐position of the secondary amine in the quenching of O2? was demonstrated. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

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