Results of ESR studies are presented for a number of radical ions selected from several classes of compounds of current interest. The strikingly different hyperfine data for the radical cations of 1,6:8,13-propane-1,3- and 1,6:8,13-ethane-diylidene-[14]annulene demonstrate the effect of an interplay of homoconjugative, inductive and hyperconjugative perturbations. The unusually stable radical cations of N,N′-dimethyl- and N,N′-trimethylene-1,6:8,13-bisimino[14]annulene should be regarded as N-centered radicals with an N-N 3-electron σ-bond. Despite similar geometries of [2.2]paracyclophane , its 1,1,2,2,9,9,10,10-octa-fluoro-derivative and its 1,9,-diene , the corresponding radical anions strongly differ in their electronic structure. An unexpected conformatinal interconversion is observed for the radical anion of . Electron acceptors, such as tetracyanoquinodimethane (TCNQ;) and its areno analogues, and electron donors, represented by tetrathiafulvalene (TTF;) and compounds containing the TTF system, form salts exhibiting high electronic conductivity (“organic metals”). ESR spectra of the radical anions and trianions of these acceptors and the radical cations of these donors provide detailed information about the spin distribution in the respective species. 相似文献
In the electron transfer between the cation radicals of the amine moiety of four intramolecular anthra cene-amine systems and the anion radicals BXXX of some heterocyclic and carbonyl compounds in acetonitrile/toluene, the triplet state of the anthracene moiety is formed. As intermediates in this process, intramolecular and intermolecular triplet exciplexcs or and or are discussed. 相似文献
Careful addition of 1,3-dibromopropane to magnesium in Et2O yields 1,3-bis(bromomagnesio)propane which is purified via “magnesacyclobutane” . Reactions of with H2O, CO2, HgBr2 and Me3SnCl are reported. MgBr2 catalyses the decomposition of to allylmagnesium bromide . 相似文献
The cyclometallated monohydrides (R H or Me) react with NaOPri/PriOH/H2 to give fluxional tetrahydrides, probably . These are highly fluxional having magnetically equivalent hydridic hydrogens, even at ---100°C. When treated with HBr, , gives and with CO it gives a mixture of complexes which are probably (2 isomers) and . When treated with ButNC this tetrahydride undergoes similar reactions but another (major) product is formed which appears to be binuclear and fluxional and is probably of type , with four bridging hydrogens. 相似文献
The laser flash photolysis of iodine-iodide mixtures in alcoholic solvents produces transient species absorbing in the red and near infrared region with maxima at 740 and 590 nm. The 740 nm absorption band has already been attributed to the well known I ion. In this work the 590 nm absorption band is assigned to the I radical anion which presumably could be formed by the equilibrium reaction: I + I3- ? I. The variations of the intensities of the 590 and 740 nm transient absorption bands as a function of I3? concentration, temperature and solvent, support this assignment. The kinetics of formation of I and I has been studied in solutions of tertiary butanol. An analysis of the experimental results shows that the I ion could be formed via a mechanism involving an I intermediate. 相似文献
Radical formation during the radiolysis of polyethylacrylate (PEA) at ?196°C has been investigated by ESR. Partially deuterated samples of PEA were used to improve the identification of radicals. It is found that ethyl radicals are formed. They originate from ion-electron recombination since they are not observed in the presence of pyrene as electron scavenger. They add to the C = O double bond leading to the formation of the radical which is found after γ-irradiation. This radical decomposes under the action of visible light to give C2H5· and PEA. This reaction is reversible. Furthermore, the radicals and are formed during the radiolysis.Chlorine substitution in the ethyl-ester group (PCIEA) enhances radical formation by a factor of 3–4. The only radical observed at low temperature is It is formed by dissociative electron capture resulting in the cleavage of the whole side chain. After heating to –10°C, in PEA and PCIEA only the radical is observed which results from main chain scission. The results of ESR are correlated with investigations on product formation, crosslinking and main chain scission given in a previous paper. 相似文献
Theoretical consideration reveals a unique relationship between NMR spectral parameters and possible types of the gramididin A spatial structure. By means of two dimensional NMR spectroscopy four distinct species were detected simultaneously in ethanol solution. Comparison of experimental data and theoretical conclusions demonstrates that species 1 and 2 are left-handed parallel double helices differing in relative arrangement of the two polypeptide chains within the dimers, species 3 is left-handed antiparallel double helix , and species 4 is a mirror image of species 1, i.e. right-handed parallel double helix . The results are compared with those on spatial structures of the peptide in complex with cesium (right-handed antiparallel double helix ) and of the gramicidin A transmembrane ionchannel (N-terminal to N-terminal single-stranded dimer ). 相似文献
A series of o-tropyliobiphenyl tetradfluoroborates has been synthesized. Evidences are presented to show that exhibit strong intramolecular charge-transfer interaction between tropylium ion and remote aryl ring. The structure of was determined by single crystal X-ray diffraction study. 相似文献
Chlorine fluorosulfonate adds exceptionally easy not only to various alkenes, perfluorobenzene, but to alkynes too The addition of peroxydisulfuryldifluoride to alkyl- and perfluoroalkyliodides leads to unstable adducts, which decompose with the formation of alkylfluorosulfonates and iodine fluorosulfonate; the latter was trapped with fluoroalkenes The use of ClOSO2F allows to substitute selectively for the fluorosulfonate group the chlorine atom in monochloroacetic acid esters as well as the fluorine atom in hexafluoroacetone N-fluoroimine ClOSO2F serves as an exceptionally active chlorinating reagent for fluorinated alcohols, nitrosocompounds, perfluoroacid amides and particularly for benzene The reaction of (OSO2F)2 with perfluoroacid amides leads to the corresponding N,N-bis(fluorosulfonate)amides, which easily rearrange into alkylfluorosulfonates The hypochlorites of fluorinated alcohols are stable enough and they, similarly to ClOSO2F, are able to add to alkenes, fluoroalkenes (but not to perfluoroisobutylene), bis(trifluoromethyl)ketene, trifluoromethylisocyanate and perfluoronitriles The fluorosulfonatoacetic acid esters are unstable at the ambient temperature, but they can be widely used in situ as a very effective alkylating reagents 相似文献
The reaction of an aromatic lithium reagent, LiR, with a perfluoroacid anhydride (RfCO)2O, in ether solution at low temperatures, produces esters of composition in addition to the expected ketone . Mixed esters of composition may be prepared by starting with a ketone and reacting with a lithium reagent LiR followed by perfluoroacid anhyride (RfCO2O. Hydrolysis of the esters provide a convenient route to trertiary alcohols of composition Rf(R) 2COH. 相似文献
Chemically induced degradation of polystyrene (PSt) in the presence of 2,4,6-tri-chloronitrosobenzene (TCNB) as radical generator was investigated in benzene solution by means of the electron spin resonance (ESR) method. The ESR spectra observed after the addition of TCNB to PSt in benzene solution were assigned to the nitroxide radicals (spin adducts) of the PSt radicals, , and . These assignments were deduced from comparisons between observed and computer simulated spectra and were supported by experiments using α-deuterated PSt. It was found by analyses of ESR spectra that two kinds of type (B) radicals were produced, which were different in local conformation. The radicals (A) and (B) were thought to be produced by hydrogen abstraction by the chlorinated phenyl radical which results from homolytic scission of the CN bond of TCNB on slight warming. On the other hand, it was concluded that β-scission of radical (A) results in the formation of the chain scission radical (C). The mechanism of degradation of PSt induced by TCNB as radical initiator is discussed, together with the decrease in molecular weight observed after the addition of TCNB to a PSt-benzene solution. From the decrease of molecular weight it is concluded that TCNB acts as a scission inducer. 相似文献
“doping-addition” of 2-NO2C6H4SCl to the tricyclo[4,2,2,02,5]deca-3,7,9-triene system occurs to give unusual products: (i) rearranged caged cyclopropane and (ii) the stable cross-perchlorate . 相似文献
Product study and kinetic data of the solvolysis of the bridgehead chlorides () and ( indicate the neighboring group participation of the strained bridgehead double bonds. 相似文献
The stereoselective fluorination of four couples of diastereoisomeric 2-alkyl 3-hydroxy 3-phenylpropanoic methyl esters by the reaction of the phenyltetrafluorophosphorane with the corresponding trimethylsilylethers derivatives is described. The structure of the 2-alkyl 3-fluoro 3-phenyl propanoic methyl esters obtained quantitativly has been determined unambiguously by NMR analysis. 19F NMR results permit us to determine the relative populations of the rotamers for each of the isomers threo and erythro. 相似文献
The standard enthalpy of formation of tellurium tetrafluoride has been determined: by combustion in fluorine: by reaction in a normal solution of soda: 相似文献
Electrokinetic phenomena in porous membranes were studied in the framework of the linear thermodynamics of irreversible processes. Phenomenological coefficients of two commercial porous membranes were determined. The variation of these coefficients with the different concentrations of NaCl used was also studied. Onsager's reciprocal relationship between cross-coefficients holds within the limits of experimental error.Membrane potentials were measured at concentrations ranging from 10?3M to 75 X 10?3M. The apparent transport number of the cation, , was calculated from the diffusion potential expression. An electrometric method was used to obtain the true cation transport number, , and the water transport number, , for different solution concentrations, ranging from 15 x 10?3M to 75 x 10?3M. The true transport number of the cation, , was also determined, taking into account water transport across the membrane. A good agreement was found between and values. 相似文献
(+-)-3,3,7-Trimethyl-2,9-dioxatricyclo[4.2.1.04, 7]noname and (+-)-3,3,7-trimethyl-2,9-dioxatricyclo[3.3.1.04, 7] nonane were synthesized. The latter was shown to be (+-)-lineatin, an ambrosia beetle pheromone. 相似文献
(R = 2,4,6-tri-t-butylphenyl) and (R = 2,4,6-tri-t-butylphenyl) are two new nickel complexes with a 1,3-diphosphaallyl ligand. Both structures have been determined by X-ray analysis. 相似文献
Reduction of α,β-unsaturated iminium salts by 3,5-dicarbethoxy-2,6-dimethyl-1,4-dihydropyridine results in or (primary) reduction products, depending on the basicity of the amine component. 相似文献