Substituent effects on electroreduction of the carbon-halogen bond

1981 ◽  
Vol 34 (11) ◽  
pp. 2331 ◽  
Author(s):  
RS Abeywickrema ◽  
EW Della
Keyword(s):  
Reduction Potential ◽  
Halogen Bond ◽  
Substituent Effects ◽  
High Yield ◽  
Polarographic Reduction ◽  
Electric Field Effects ◽  
Controlled Potential Electrolysis ◽  
Half Wave ◽  
Controlled Potential ◽  
Substituted 1

Polarographic reduction of a series of 4-substituted 1-iodobicyclo[2,2,2]octanes has been examined in an attempt to assess the effect of substituents on the half-wave reduction potential. It is found that the values of E� do not show a linear correlation with the relevant σ1 constants; the deviations are discussed in terms of the relative importance of the steric and electric field effects of the substituent. Controlled-potential electrolysis of a number of the substrates reveals that the hydrocarbon corresponding to fission of the carbon-iodine bond is formed in high yield.

Substituent effects on polarographic reduction of some photographic color intermediates

1976 ◽  
Vol 54 (8) ◽  
pp. 1205-1210 ◽  
Author(s):  
Ahmad S. Shawali ◽  
Bahgat E. El-Anadouli
Keyword(s):  
Dissociation Constants ◽  
Substituent Effects ◽  
Protonated Form ◽  
Acid Dissociation ◽  
Polarographic Reduction ◽  
Substituent Constant ◽  
Acid Dissociation Constants ◽  
Controlled Potential Electrolysis ◽  
Half Wave ◽  
Controlled Potential

Polarographic reduction of two series of benzoylacetanilides has been investigated in 40% (by volume) ethanolic Britton–Robinson buffers. One series (A) contains substituents on the anilide moiety, and the second (B) has substituents on both the anilide and benzoyl moieties. Polarographic controlled-potential electrolysis data indicate that the electroactive species in both series is the protonated form (ArCOCH2CONHAr′)H+. The reduction half-wave potentials of anilides of series A were found to be independent of the nature of the substituent, whereas those of series B show a good linear relationship when plotted vs. the σ substituent constant of the substituent on the benzoyl moiety (ρ = 0.284, r = 0.995). Values of the acid dissociation constants of the keto (K1) and enol (K2) tautomers of the anilides of series A were calculated; unlike their E1/2 values, the pK1 data show a linear correlation with the Hammett substituent constant, σ. The pK2 values show, however, little variation with σ.

scholarly journals Differential Pulse Polarographic Determination of Procymidone in Formulations and Wine

2002 ◽  
Vol 85 (3) ◽  
pp. 731-735 ◽  
Author(s):  
Neelam Y Sreedhar ◽  
Thommandru R Babu ◽  
Kethamreddy Samatha ◽  
Devarapalli Sujatha ◽  
Thenepalli Thriveni
Keyword(s):  
Reduction Process ◽  
Differential Pulse ◽  
Differential Pulse Polarography ◽  
Experimental Conditions ◽  
Controlled Potential Electrolysis ◽  
Pulse Polarography ◽  
Half Wave ◽  
Single Well ◽  
Controlled Potential ◽  
Ph Range

Abstract The dicarboximide fungicide procymidone was studied systematically by using direct current polarography, cyclic voltammetry, differential pulse polarography (DPP), controlled potential electrolysis, and millicoulometry in the universal buffer medium with dimethylformamide as the solvent. Procymidone exhibited a single well-defined polarographic wave in the pH range 2.0–6.0, leading to the formation of the hydroxy compound. The overall reduction process was diffusion-controlled and adsorption-free. The variation of half-wave potential with pH, the concentration of the analyte, and other experimental conditions are described. The reduction mechanism proposed is an overall 4-electron process, in which the dicarboximide group is reduced. DPP was used to determine procymidone in agricultural formulations and wine at the optimum conditions found; a detection limit of 2.4 × 10−9M was estimated. The results obtained by the proposed method were also compared with those obtained by other methods.

On the One and Two-Electron Oxidations of Water-Soluble Zinc Porphyrins in Aqueous Media

1981 ◽  
Vol 36 (5) ◽  
pp. 596-600 ◽  
Author(s):  
Michael Neumann-Spallart ◽  
K. Kalyanasundaram
Keyword(s):  
Cyclic Voltammetry ◽  
Aqueous Media ◽  
Water Soluble ◽  
Chemical Methods ◽  
Controlled Potential Electrolysis ◽  
Half Wave ◽  
Controlled Potential ◽  
Zinc Porphyrins ◽  
The One ◽  
Soluble Zinc

The one and two-electron oxidations of water soluble ionic zinc porphyrins (Zinctetra-methylpyridylporphyrin, ZnTMPyP, Zinc-tetra-p-sulfonato-phenyl-porphyrin, ZnTPPS, and Zinc-tetra-p-carboxy-phenylporphyrin, ZnTPPC) leading to the porphyrin Π-cations and Π-dications have been investigated in water by electrochemical (cyclic voltammetry and controlled potential electrolysis) and chemical methods. The half-wave potentials for the oxidation are shown to be markedly dependent on the charge on the β-substituents. While the one-electron oxidations for all these porphyrins are reversible, the dication formation leads to labile isoporphyrins as intermediates

Polarographic reduction of p–substituted 1-phenyl-3-aminocarbonylpyridinium salts

1987 ◽  
Vol 52 (6) ◽  
pp. 1550-1560
Author(s):  
Jiří Krechl ◽  
Daniela Mižaninová ◽  
Jiří Volke ◽  
Josef Kuthan
Keyword(s):  
Supporting Electrolyte ◽  
Substitution Effect ◽  
Heterocyclic Ring ◽  
Reduction Wave ◽  
Polarographic Reduction ◽  
Benzene Nucleus ◽  
Half Wave ◽  
The One ◽  
Low Sensitivity ◽  
Substituted 1

The substitution effect of different groups (H, NO2, COOH, Br, Cl, NHCOCH3, CH3, OCH3, OH, and N(C2H5)2) on the polarographic behaviour of p–substituted 1-phenyl-3-aminocarbonylpyridinium cations has been investigated, in particular on their half-wave potentials in aqueous phosphate buffers pH 6·65 (10% DMF) and in anhydrous solutions of dimethylformamide with 0·05 mol l-1 (n-C4H9)4N+BF4- as supporting electrolyte. The half-wave potentials of the reduction wave which corresponds to the uptake of a single electron (wave B) and to the formation of the primary radical, obey a Hammett correlation in a similar way as it is in the case of 1-benzyl-3-aminocarbonylpyridinium cations. The slope ρπ,R in the Hammett plot equals 0·093 V for 10% DMF and 0·179 V for anhydrous DMF and compares thus with this slope obtained with the 1-benzyl derivatives where 0·095 V was found for water and 0·127 V for anhydrous acetonitrile. The transfer of the substitution effect from the substituent in the para position on the benzene nucleus to the heterocyclic ring in thus equally active in both substances and depends more strongly on the solvent than on the structure of cations of both types. The low sensitivity in both series towards a change in the substituent is explained by the fact that during the uptake of the electron the benzene and the pyridine nucleus are not even approximately coplanar. This is why the π-overlap between the two nuclei is considerably restricted. The analysis of sampled dc-polarographic waves has confirmed that the one-electron uptake is followed by a chemical reaction, most probably a dimer formation or a reaction of the primary product with the starting substance.

Polarography of coordinated oximes

1971 ◽  
Vol 24 (10) ◽  
pp. 2089 ◽  
Author(s):  
OGB Nambiar ◽  
PR Subbaraman
Keyword(s):  
Alkaline Solution ◽  
Potential Range ◽  
Polarographic Reduction ◽  
Acid Solutions ◽  
Controlled Potential Electrolysis ◽  
Controlled Potential ◽  
Parent Ligand

The polarographic reduction of dimethylglyoxime, cyclohexane-1,2-dione dioxime (nioxime), α-furil dioxime, and salicylaldoxime chelated to cobalt(II) and iron(II) has been investigated. Unlike the parent ligand, the reduction of the coordinated ligand proceeds in two equal steps in acid solutions. The intermediate half-way stage is suggested to be the hydroxylamine of the oxime. Results of the controlled potential electrolysis of the cobalt(II)-dimethylglyoxime chelate also supports this view. In alkaline solution reduction stops at the half- way stage since the product of half-way reduction, presumably the corresponding hydroxylamine, is not further reduced in the available potential range. The first step of reduction occurs invariably at a potential less negative than that of the parent ligand.

Spectroscopic and electrochemical properties of intramolecularly hydrogen-bonded compounds. Ortho-hydroxyazobenzenes

1981 ◽  
Vol 59 (5) ◽  
pp. 821-827 ◽  
Author(s):  
Salvatore Millefiori ◽  
Arcangelo Millefiori
Keyword(s):  
Bond Formation ◽  
Substituent Effects ◽  
Lone Pair ◽  
Intramolecular Hydrogen Bonding ◽  
Photoelectron Spectra ◽  
Polarographic Reduction ◽  
Reduction Potentials ◽  
Half Wave ◽  
Experimental Findings ◽  
Intramolecular Hydrogen

The gas-phase uv photoelectron spectra and the half-wave polarographic reduction potentials in acetonitrile solutions of a series of 2-hydroxy-5-methylazobenzene have been determined. The first three IP's and the E1/2 values were linearly correlated with σ+ and σ constants, respectively. E1/2 can also be linearly related to the energy of the lowest unoccupied molecular orbital. Effects of the intramolecular hydrogen bonding on the pe spectra and on the polarographic reduction of the title compounds were evaluated by comparing the experimental findings in 2-hydroxy-5-methylazobenzene, 2-methoxy-5-methylazobenzene, and p-hydroxyazobenzene. On H-bond formation, the antibonding combination of the two nitrogen lone-pairs, n−, and the oxygen lone-pair is ionized at a slightly higher energy and at a lower energy, respectively, than in the non H-bonded compound. The first π-ionization band is slightly lowered in energy in the non H-bonded structure, probably owing to a normal substituent effect. These features are not maintained in the 4'-nitro derivative, where the band encompassing the n− ionization remains at the same potential in both structures, while the first π band in the non H-bonded compound moves toward higher IP. Spectral differences between the bonded and nonbonded structures are the result of a balance of substituent effects, and of both hydrogen bond and orbital interactions. The solution electron affinity of the studied compounds increases on H-bond formation by an amount comparable with the experimental strength of the H-bonding. INDO/S-CI calculations are in qualitative agreement with the experimental results.

Substituent effect in addition of cyanide ion to p-substituted 1-benzyl-3-carbamoylpyridinium chlorides

1983 ◽  
Vol 48 (5) ◽  
pp. 1401-1407 ◽  
Author(s):  
Františka Pavlíková-Raclová ◽  
Josef Kuthan
Keyword(s):  
Aqueous Solutions ◽  
Rate Constants ◽  
Substituent Effect ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Cyanide Ion ◽  
Quaternary Salts ◽  
Half Wave ◽  
Substituted 1 ◽  
Mechanism Of The Reaction

The rate constants k2 and equilibrium constants K = k2/k-2 of the title process (A) have been measured in aqueous solutions of eight quaternary salts of nicotinamide I (R = p-XC6H4CH2) at 298 K. The substituent effects of X = CH3O, CH3, H, F, Cl, COOCH3, CN, and NO2 exhibiting the Hammett dependence have been correlated with half-wave potentials of reduction of the depolarizers I, and the correlation results have been discussed with respect to mechanism of the reaction (A).

Polarographic reduction of 1-(p-substituted benzyl)-3-cyanopyridinium chlorides

1983 ◽  
Vol 48 (8) ◽  
pp. 2273-2283
Author(s):  
Františka Pavlíková-Raclová ◽  
Josef Kuthan
Keyword(s):  
Substituent Effects ◽  
Polarographic Reduction

Reduction of 3-cyanopyridinium salts has been studied on the mercury dropping electrode. Solvent and substituent effects and pH of the medium have been shown to modify in a certain extent differently the polarographic characteristics as compared with analogous 3-carbamoyl derivatives, which is due to higher electronegativity of the studied cations.

1-Carba-arachno-pentaborane(10) Derivatives

1997 ◽  
Vol 62 (8) ◽  
pp. 1254-1262 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Hans-Jörg Schanz
Keyword(s):  
High Yield ◽  
Exchange Reactions ◽  
Nmr Data ◽  
Substituted 1 ◽  
C Nmr

The formation of organo substituted 1-carba-arachno-pentaborane(10) derivatives is shown to proceed in high yield via in situ generated 1,1,1-tris(diethylboryl)propane (2) from diethyl(propyn-1-yl)borane (1) by hydroboration with an excess of diethylborane (hydride bath). In the hydride bath, exchange reactions between 2 and other geminal bis(diethylboryl)alkanes take place until the carbaborane skeleton is formed. If tris(diethylboryl)methane is used under the same conditions, the corresponding 1-carba-arachno-pentaborane(10) derivatives 11 and 12 are formed in mixture with other unknown boranes or carboranes. 11B and 13C NMR data are presented to allow for straightforward identification of the 1-carba-arachno-pentaboranes(10).

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