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121.
Tatsuro Gueshi Koichi Tokuda Hiroaki Matsuda 《Journal of Electroanalytical Chemistry》1978,89(2):247-260
Equations for chronopotentiometry and chronoamperometry at partially covered electrodes have been derived using a model of hexagonal array of cylidrical spaces terminated, at the electrode surface, by concentric active and inactive regions. The boundary value problem was shown to be analogous to that for a charge transfer preceded by a chemical reaction. Experiments with the reduction of ferricyanide on gold model electrodes partially covered with photoresist layer showed excellent agreement with the theory. Application of the equations to estimation of coverage and size of active sites distributed on a electrode surface is discussed. 相似文献
122.
Preliminary studies of the reaction of chlorine with tetramethylsilane and hexamethyldisilane in the gas phase show that the photochlorination of tetramethylsilane is complex, giving different products from the corresponding reaction in solution and having an explosion boundary. At pressures below the explosion boundary the main products are ethylene, hydrogen chloride, dimethylchlorosilane, and more highly chlorinated methylsilanes. Above the explosion boundary main products after explosion are methane, acetylene, ethylene, hydrogen chloride, and silicon tetrachloride. Hexamethyldisilane reacts rapidly with chlorine in the dark, as it does in solution, forming mainly trimethylchlorosilane along with similar products to those found with tetramethylsilane. Subsequent photochlorination of trimethylchlorosilane follows a similar course to that of tetramethylsilane in the gas phase. Tentative mechanisms involving “hot” molecules are suggested. 相似文献
123.
N.E. Kolobova A.B. Antonova O.M. Khitrova M.Yu. Antipin Yu.T. Struchkov 《Journal of organometallic chemistry》1977,137(1):69-78
The novel complexes CpRe(CCHPh)(CO)2 and Cp2Re2(μ-CCHPh)(CO)4 containing a terminal and a bridging phenylvinylidene ligand respectively and the binuclear complex Cp(CO)2Re[CC(Ph)C(Ph)CH2]Re(CO)2Cp were obtained in the reaction of CpRe(CO)3 with PhCCH.According to an X-ray study of the latter complex the unusual bridging ligand is η1-bonded to one Re atom and η2-bonded to the other. 相似文献
124.
James Y. Becker Larry L. Miller Frank R. Stermitz 《Journal of Electroanalytical Chemistry》1976,68(2):181-191
The electrochemical oxidation of the alkaloid laudanosine (Ia) to O-methylflavinantine (II) has been studied in acetonitrile solvent. Using cyclic voltammetry, rotating disc voltammetry and preparative electrolyses on several alkaloids, simple aliphatic amines and aromatic compounds, some aspects of the mechanism of this coupling reaction are elucidated. The first anodic wave for laudanosine at platinum has Ep=0.55 V vs. Ag/Ag+. The electrode rapidly becomes partially passivated at potentials above 0.5 V. This is due to a film which “dissolves” below 0.5 V, at a rate independent of the potential. It is shown that the reaction (Ia)→(II) proceeds at 0.5 V by initial oxidation of the amine moiety. If acids such as sodium bicarbonate are added to the anolyte the amine is protonated causing the first wave to disappear. Oxidation at 1.1 V under these acidic conditions produces the same product, but more rapidly and in significantly higher yield because electrode filming and side reactions resulting from the amine oxidation are abrogated. 相似文献
125.
The shift of the uncoupled OH stretching frequency of water (from its free state position) in crystal hydrates has been plotted against a parameter r0 obtained by subtracting the H-bond (OH...Y) length from the sum of the free state ionic radii of O and Y. From an analysis of this curve it is inferred that MOw coordination in hydrates reduces the ionic size of water oxygen and its effect on the OH stretching frequency is opposite to that of H-bonding. 相似文献
126.
A systematic study of the adsorption and interfacial behaviour of the adenine mono-nucleotides (5′-AMP, 3′-AMP, cyclic 3′,5′-AMP, 5′-ADP and 5′-ATP) and adenosine for comparison at the HMDE has been carried out at pH 3.4 to 3.5. Thus, the N(1) of the adenine moiety is protonated to a major extent.The adsorption was followed by single sweep voltammetry (measurement of the time integral of the reduction peak of the adsorbed adenine moiety) and by a.c. voltammetry (out-of-phase component of the a.c. response being proportional to the differential double layer capacity). In this paper the situation corresponding to a “dilute” adsorption layer existing at low bulk concentrations is studied for various degrees of coverage. The potential dependence of the coverage is of bell shaped type with an extended maximum region around the potential of electrocapillary maximum (Eecm) of the blank. For the same bulk concentration the coverage decreases in the series AMP, ADP, ATP, i.e. with increasing negative charge of the nucleotide, and at the same time the potential range of adsorption narrows. Among the monophosphates the coverage decreases in the series 3′-AMP, 5′-AMP, cyclic 3′,5′-AMP. The variations are connected with the varying charge of the mononucleotides and with the possibilities for interactions with adjacent molecules in the adsorption layer.At elevated bulk concentrations above a threshold value a substantial increase in coverage occurs around Eecm as due to strong interactions between the adsorbed base moieties a rather compact film is formed. 相似文献
127.
An unambiguous synthesis of Cypridina etioluciferamine was accomplished in order to prove the structure of this important bioluminescent natural product. Several 2-aminopyrazine 1-oxides were synthesized in order to establish a spectroscopic method for determining the placement of substituents on the pyrazine nucleus of Cypridina etioluciferamine. Titanium tetrachloride was used to improve the yields of these compounds; for example, the yield of 2-amino-3-methyl-5-phenylpyrazine 1-oxide (19) from reaction of phenylglyoxal 1-oxime and α-aminopropionitrile was raised from 3% to 51% by the use of titanium tetrachloride. The pyrazine ring proton is found at τ 1·37 (DMSO-d6). The isomeric 2-amino-3-methyl-6-phenylpyrazine 1-oxide (22) was similarly prepared and its pyrazine ring proton is found at τ 2·18. This large difference (0·81 ppm) in chemical shift was used to determine whether a 2-aminopyrazine 1-oxide was 5- or 6- substituted. Prepared in an analogous fashion were 2-amino-5-(indol-3-yl)-3-methylpyrazine 1-oxide (23) and 2-amino-5-(indol-3-yl)-3-(3-phthalimidopropyl)pyrazine 1-oxide (16). The structures of these compounds were verified by NMR spectroscopy. By treatment with Raney nickel and hydrogen gas, then 100% hydrazine hydrate, 16 was converted to 2-amino-3-(3-aminopropyl)-5-indol-3-ylpyrazine (5), isolated as the dihydrochloride. This compound, with the indole moiety definitely placed at C-5, is identical with Cypridina etioluciferamine dihydrochloride (IR, UV, TLC). These results show that the structures of Cypridina etioluciferamine and luciferin are correct as published. 相似文献
128.
Mary McPartlin 《Polyhedron》1984,3(12):1321-1328
The recently developed electron-counting rules for condensed polyhedral metal carbonyl clusters have been utilised to develop a systematic approach for enumerating the structural alternatives for metal cluster compounds which are isoelectronic. The more usual cluster degradation and aggregation processes are represented in a matrix form which relates the change in electron count to the number of new bonds formed (or broken). The matrices for cluster degradation and aggregation are represented in a complementary fashion so that the search for isoelectronic clusters greatly simplified. The utility of the approach is illustrated by reference to some recent examples from metal carbonyl cluster chemistry. 相似文献
129.
C. Mioskowski A. Solladie-Cavallo G. Solladie 《Journal of organometallic chemistry》1978,149(3):C63-C65
Attachment of a Cr(CO)3 moiety to one of the aromatic rings in rigid diaryl ketones of very low prochirality followed by addition of a chiral and optically pure reagent leads to satisfactory asymmetric induction ~40%. Asymmetric induction is smaller in the case of acyclic systems. 相似文献
130.
The kinetics of the reaction between organocobaloximes, RCo(DH)2H2O, and iodine have been investigated. They reveal the participation of an RCo(DH)2H2O · I2 intermediate which undergoes intramolecular transalkylation and acts as an electrophile towards a second organocobaloxime molecule. The trend in reactivity as the R group is varied is discussed. 相似文献