Ab initio computation of electron affinities of substituted benzalacetophenones (chalcones): a new approach to substituent effects in organic electrochemistry

The electron affinities (EAs) of a training set of 29 monosubstituted benzalacetophenones (chalcones) were computed at the ab initio density functional B3LYP/6-31G^* level of theory. The EAs and experimental reduction potentials of the training set are highly linearly correlated (correlation coefficient of 0.969 and standard deviation of 10.8 mV). An additional 72 di-, tri-, and tetrasubstituted chalcones were then synthesized. Their reduction potentials were predicted from computed EAs using the linear correlation derived from the training set. Agreement between the experimental and computed reduction potentials is remarkably good, with a standard deviation of less than 22 mV for this very large set of substances whose potentials extend over a range of almost 700 mV.     

Cathodic behaviour of some 5-nitrophenyl-1,2-dithiole-3-thiones and 5-nitrophenyl-1,2-dithiole-3-ones

The electrochemical behaviour of 5-(nitrophenyl)-1,2-dithiole-3-thiones and 5-(nitrophenyl)-1,2-dithiole-3-ones was studied by cyclic voltammetry in DMF. The standard reduction potentials of 5-(p-nitrophenyl)-dithiolethione and 5-(p-nitrophenyl)-dithiolone entered into a linear correlation involving standard reduction potentials of substituted nitrobenzenes and known electronic constants of several substituents. This correlation allowed the determination of the electronic effects of [3-thioxo-1,2-dithiole]-5-yl and [3-oxo-1,2-diothiole]-5-yl groups which were, respectively, σ_p⁻=1.14 and σ_p⁻=0.86, comparable with those of nitro or cyano substituents.     

Deep eutectic solvents (DES) as green reaction media for the redox isomerization of allylic alcohols into carbonyl compounds catalyzed by the ruthenium complex [Ru(η3:η3-C10H16)Cl2(benzimidazole)]

The bis-allyl Ru(IV) complex [Ru(η³:η³-C₁₀H₁₆)Cl₂(benzimidazole)] (1c) is an active catalyst in the redox isomerization of allylic alcohols into saturated carbonyl compounds using, for the first time, Deep eutectic solvents (DES) as reaction media. A series of primary and secondary allylic alcohols could be isomerized into the corresponding carbonyl compounds in the absence of base. Although high activities and selectivities were reached at short reaction times and with low catalyst loadings (0.2 mol% in Ru) for monosubstituted allylic alcohols, for their disubstituted counterparts, high catalyst loading and longer reaction times were always required. It is important to note that the catalytic system: i) is active in a large-scale experiment, and ii) could be recycled up to four consecutive runs.     

Anodic oxidation of stilbenes bearing electron-withdrawing ring substituents

A number of disubstituted stilbenes bearing either two strong electron-withdrawing groups or one electron-withdrawing and one electron-donating group were synthesized and anodically oxidized in a divided cell in methanol at a carbon anode. A variety of types of products were obtained, most of which have never been observed upon oxidation of alkenes not bearing electron-withdrawing groups. A mechanistic scheme involving 2-methoxy-1,2-diarylethyl cations as key intermediates can account for all of the observed products. The nature of the products from each alkene is strongly correlated with the sum of the Hammett σ⁺ values of the ring substituents.     

Noncovalently bonded quinone on self-assembled molecular layers

Aminoalkanethiol surface modifiers were investigated on gold electrodes. It was established, that quinone molecules could be attached to these surface layers in three different forms with well-distinguished redox potentials. Chemical reaction with the amino groups of the modifiers could produce monosubstituted and disubstituted quinones attached covalently to the layers. However, a third form could be detected, as well that seems to be quinone attached non-covalently to the monosubstituted quinone molecules.     

Adsorption of methimazole on the mercury electrode

The electrosorption behaviour of methimazole (vetranal) at the mercury/1 M NaClO₄ interface was determined from a double layer differential capacity measurements extrapolated to zero frequency. Methimazole is the thiourea derivative, which is used as a drug in the overactivity of the thyroid gland. The values of zero charge potential were shifted to negative potentials ca. 230 mV with an increasing methimazole concentration from 10⁻⁴ M to 10⁻¹ M. The relative surface excesses Γ′ of methimazole were calculated from surface pressure at the density of surface charge σ = constant. The values of Γ′ increase with the increase of σ. Adsorption of methimazole was analyzed on the basis of the constants obtained from the Frumkin and virial isotherms. The values of the standard Gibbs energy of adsorption ΔG° increase with the increase of σ while the values of interaction parameters A and B decrease.     

Nuclear magnetic resonance characterization of reaction products of interesterification of peracetylated α-d-glucopyranose and fatty acid methyl esters

Mono- and diesters of fatty acids of peracetylated α-d-glucopyranose were prepared by chemical interesterification. Substituent-induced chemical shift effects on the carbonyl carbons rather than the ring carbons and proton atoms unambiguosly show the fatty acyl substituents to be at C1 in the monosubstituted, and at C1 and C6 in the disubstituted products. ¹H nuclear magnetic resonance (NMR) integration data before and after interesterification complemented ¹³C chemical shift data in verifying the molecular structures. Empirical data from classical ¹H and ¹³C NMR experiments thus provide a simple self-contained method for determining the number and position of fatty acyl substituents, and the anomeric compositions of peracetylated glucose fatty esters.     

Mixing and fast chemical reaction—I: Test reactions to determine segregation

The coupling of 1-naphthol with diazotised sulphanilic acid produces by competitive, consecutive reactions two dyestuffs, whose concentrations can readily be measured spectrophotometrically. The reaction kinetics have been measured using the stopped-flow method and the reaction mechanism is known. Using mild reaction conditions (room temperature, aqueous solution of pH = 10, concentrations of order 0.1 mol m^?3), the product mixture always contained more disubstituted and therefore less monosubstituted dyestuff than would have been formed in the chemically controlled regime. (In these experiments the stoichiometric and volumetric ratios of the reagents were varied and the 0.063 m³ reactor was operated semi-continuously, as well as continuously using various turbine speeds). The reactions were fast enough to produce inhomogeneity at the molecular scale (segregation) and are shown to possess highly convenient properties for studying such segregation.     

Anodic thiocyanation of mono- and disubstituted aromatic compounds

The in situ and environmentally friendly thiocyanation (no use of toxic oxidizing agents) electrochemical thiocyanation of aromatic compounds involving various derivatives of anisole and aniline to afford aromatic thiocyanates have been studied in organic acidic media. The initial electrochemical step involves anodic oxidation of thiocyanate anion to its radical (SCN), followed by dimerization to thiocyanogen (SCN)₂. The latter is polarized by the acidic solvent and attacks the aromatic nucleus of the substrate to afford the corresponding thiocyanate derivative. The sole thiocyanate products obtained in each case shows high regio-selectivity (no ortho isomer was observed) for the monosubstituted aromatics and high isomer-selectivity (no isothiocyanate isomer was detected) for both mono- and disubstituted aromatics.     

Versatile electrochemically based preparation of unusual Grignard reagents containing electrophilic substituents

Upon electrochemical reduction of potassium perchlorate in dimethyl sulfoxide to potassium the strong dimsyl base (i.e. the conjugate base of dimethyl sulfoxide) is formed in the reaction of the alkali metal with the solvent. The electrolysis is performed in an undivided cell with a magnesium rod serving as sacrificial anode, thereby generating magnesium ions, which stabilize the generated dimsyl through ion-pair formation. In a second non-electrochemical step, Grignard type reagents R₂Mg are obtained simply by letting the magnesium salt of dimsyl base deprotonate weakly acidic substrates (pK_a < 26 in dimethyl sulfoxide) added to the solution. The advantage of generating these reagents through a deprotonation route rather than by reduction of halogen-substituted compounds as in the classical approach is that the substrates may contain electrophilic groups, such as halogen, carbonyl or cyano. The R₂Mg reagents react with electrophiles akin to ordinary Grignard reagents as illustrated by the preparation of several substituted benzylidenefluorenes in nucleophilic addition reactions. The electrochemical properties of the products were investigated and a reasonable linear correlation of the first reduction potentials with the Hammett substituent coefficient σ⁻ was found.     

Konformationsuntersuchungen mit Hilfe der 13C-NMR-Spektroskopie. IV. Additive Berechnung der 13C-chemischen Verschiebungen in 2-Brom-cycloalkanolen und 2-Brom-1-methoxy-cycloalkanen unterschiedlicher Ringgröße

Conformational Investigations by Means of ¹³C-N.M.R.Spectroscopy. IV. Additive Calculation of the ¹³C-N.M.R. Chemical Shifts in 2-Bromo-cycloalkanoles and 2-Bromo-1-methoxy-cycloalkanes of Different Ring Size The ¹³C-n.m.r. spectra of a series of bromo-cycloalkanes, cycloalkanoles, methoxy-cycloalkanes, trans-2-bromo-cycloalkanoles and trans-2-bromo-1-methoxy-cycloalkanes (ring size n = 5, 6, 7, 8, 12) as well as cis-2-bromo-cyclododecanol and cis-2-bromo-1-methoxycyclododecane are obtained and assigned. The ¹³C-chemical shifts of the monosubstituted compounds have been used to estimate the substituent effects of bromo, hydroxy and methoxy groups to the α-, β- and γ-position. Using these shift parameters, the ¹³C-chemical shifts of the vicinal disubstituted compounds are calculated in an additive incremental manner. These ¹³C-chemical shifts have been compared with the experimental values and the differences are discussed with respect to the magnitude of the deviations from additivity with the dimension of steric and electronic interaction of the vicinal substituents.     

Imidocarbocyanines—spectral sensitizers of photographic silver halide emulsions

The review deals with the main results of several investigations of the relationship between the chemical structure of imidocarbocyanines and their basicity, redox potentials and photographic action in silver halide emulsions. A number of quantitative and qualitative relationships connecting p K_a and E_1,2^Ox(Rcd) of imidocarbocyanines and the Hammett σ_p-constants of different electronic substituents ranging from CH₃O (σ_p = ?0·27) to CF₃SO₂ (σ_p = 0·96) and the Taft σ^*-constants of groupings attached to the nitrogen atom (alkyl, aryl, ω-trifluoromethylalkyl or sulphoalkyl), are discussed. The main factors contributing to the total effect of spectral sensitization of silver halide emulsions by imidocarbocyanines are analyzed and a relationship between the degree of suppression of their sensitizing action by colour components and the tendency to aggregate on the surface of silver halide crystals is established.     

Mecanisme de la reduction electrochimique d'indenones-2,3 disubstituees

At a mercury cathode, in aqueous alcoholic media, the electroreduction at low potential of 2–3 disubstituted indenones can lead to the parent-indanones. The stereochemical analysis of the results needs to be acquainted with the electrochemical mechanism; undoubted assumption of the latter is difficult, as regards inhibition that occurs at some experimental conditions, due to the diol resulting to the first 1e reduction step.In acidic media, according to the sequence H⁺eeH⁺, the polarogram of very diluted solutions shows a single 2e wave; for more concentrated samples, the polarographic curve separates in two waves, the heights of which are equivalent. At any case, the enolic form of the indanone is obtained at the electrode.In basic media, pH being less than 12, the reduction leads directly to the indanone. The mechanism eH⁺eH⁺ (single 2e wave) predominates. As pH increases, it is, little by little, supplanted by the sequence eeH⁺H⁺ (two distinct 1e waves) but this has been undoubtedly established only in the case of 2–3 dimethyl-indénone.     

Global uncertainty assessments by high dimensional model representations (HDMR)

A general set of quantitative model assessment and analysis tools, termed high-dimensional model representations (HDMR), have been introduced recently for high dimensional input-output systems. HDMR are a particular family of representations where each term in the representation reflects the independent and cooperative contributions of the inputs upon the output. When data are randomly sampled, a RS(random sampling)-HDMR can be constructed, which is an efficient tool to provide a fully global statistical analysis of a model. The individual RS-HDMR component functions have a direct statistical correlation interpretation. This relation permits the model output variance σ² to be decomposed into its input contributions σ²=∑_iσ_i²+∑_i<jσ_ij²+? due to the independent variable action σ_i², the pair correlation action σ_ij², etc. The information gained from this decomposition can be valuable for attaining a physical understanding of the origins of output uncertainty as well as suggesting additional laboratory/field studies or model refinements to best improve the quality of the model. To reduce sampling effort, the RS-HDMR component functions are approximately represented by orthonormal polynomials. Only one randomly sampled set of input-output data is needed to determine all σ_i, σ_ij, etc. and a few hundred samples may give reliable results. This paper presents its methodology and applications on an atmospheric photochemistry model and a trace metal bioremediation model.     

Studies concerning charged nickel hydroxide electrodes. VIII. The relative potentials of the β-/γ -nickel oxy hydroxide reduction processes

In this communication it is demonstrated that a partly chargedβ-Ni(OH)₂/β-NiOOH couple can oxidizeα-Ni(OH)₂ to theγ-phase. This observation is in accordance with the order of the reversible potentials and illustrates the greater stability of theγ-phase in 7 mol dm^?3 KOH. Contrary to several claims in the literatureβ-NiOOH undergoes reduction over a range of potentials from 400 to 300 mV wrt Hg/HgO/KOH whilst theγ-phase containing Ni⁴⁺ species undergoes reduction usually at less positive potentials (below 300 mV). Internal oxidation/reduction reactions between various α/γ and β/β-phase couples can be expected to take place in partly charged electrodes during open circuit stand periods in addition to oxygen evolution. Ageing of oxidized phases may also lead to changes in free energies. Both types of process may lead to shifting of peaks after open circuit stand periods.     

Electrochemical and mARC‐Catalyzed Enzymatic Reduction of para‐Substituted Benzamidoximes: Consequences for the Prodrug Concept “Amidoximes instead of Amidines”

The mitochondrial amidoxime reducing component (mARC) activates amidoxime prodrugs by reduction to the corresponding amidine drugs. This study analyzes relationships between the chemical structure of the prodrug and its metabolic activation and compares its enzyme‐mediated vs. electrochemical reduction. The enzyme kinetic parameters K_M and V_max for the N‐reduction of ten para‐substituted derivatives of the model compound benzamidoxime were determined by incubation with recombinant proteins and subcellular fractions from pig liver followed by quantification of the metabolites by HPLC. A clear influence of the substituents at position 4 on the chemical properties of the amidoxime function was confirmed by correlation analyses of ¹H NMR chemical shifts and the redox potentials of the 4‐substituted benzamidoximes with Hammett’s σ. However, no clear relationship between the kinetic parameters for the enzymatic reduction and Hammett’s σ or the lipophilicity could be found. It is thus concluded that these properties as well as the redox potential of the amidoxime can be largely ignored during the development of new amidoxime prodrugs, at least regarding prodrug activation.     

Reduction electrochimique de gem-dichloro-succinimides. Etude stereochimique

Electroreduction of 3,3-dichlorosuccinimides, disubstituted at C—4 by an alkyl and phenyl group, leads to a mixture of two monochloro derivatives: (i) whatever the starting compound, preferential formation of the trans isomer is observed when electrolyses are carried out in a basic media (ammoniacal buffer), (ii) in acidic media (acetic buffer or sulphuric acid), N-alkyl-succinimides give rise to an excess of the cis isomer when reductions are performed at very cathodic potentials.     

Stereochimie de l'electroreduction de bromocyclopropanes—III. Diastereoselectivite de la reduction electrochimique de gem-dibromocyclopropanes

Cleavage of a single carbon bromine bond occurs in the two electrons reduction of 2,2 disubstituted 1,1 dibromo cyclopropanes.Analysis of the diastereoisomeric mixture of monobromo compounds obtained at the term of electrolysis at a mercury cathode in a hydroethanolic media allows to determine which of the two bromine atoms is preferentially cleaved.

When R² = Ph, R¹ = H or CH₃ only a low stereoselectivity is generally observed. Nevertheless, yields up to 84% of the cis isomer are achieved when R¹ = H.Best results are obtained when R² is a carboxy group (CO₂H, CO₂Me or CO₂Et) especially when the reduction is carried out in the presence of quaternary ammonium cations. The cis isomer is always preferentially formed; yields up to 92% when R² = CO₂H and R¹ = Ph, and up to 99% when R² = CO₂Et and R¹ = CH₃ can be achieved.Influence of electrolyses conditions (working potential, nature of the supporting electrolyte) on the stereochemical course of the reduction is investigated.     

Influence of DGEBA crosslinking on Li ion conduction in poly(ethyleneimine) gels

We characterize the DC conductivity (σ₀) of solution electrolytes prepared by adding LiCF₃SO₃ (LiTf) salt to a (50/50 w/w) solution of branched poly(ethyleneimine) (PEI) in N,N-dimethylformamide (DMF). The value of σ₀ increases with decreasing LiTf concentration over the range of compositions studied due to the formation of contact ion pairs at higher LiTf concentrations, with the highest value of σ₀ exceeding 10⁻³ S cm⁻¹ at 20 °C. Rubber-like gel electrolytes are prepared by epoxide-amine crosslinking of selected solutions by addition of diglycidyl ether of bisphenol A (DGEBA). Holding the [N]:[Li] mole ratio fixed, increasing the crosslink density dramatically decreases σ₀ at all temperatures studied. The decrease in σ₀ cannot be attributed to an increase in the glass transition temperature, as little variation in T_g is noted amongst the samples due to their high solvent content. Rather, we propose that the decrease in conductivity is due to loss of fast segmental motions associated with chain ends, which become tethered to the network upon crosslinking.     

Effect of Head Groups,Temperature, and Polymer Concentration on Surfactant—Polymer Interactions

The micellization behaviour of sodium dodecyl sulphate, sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and cetylpyridinium chloride in water and in aqueous solutions of polyethylene oxide (PEO, molecular weight = 100,000) having concentrations (0.005–0.04 %, w/v) has been studied at different temperatures (288.15–318.15 K) using conductivity, surface tension, and viscosity methods. From conductivity measurements various micellar parameters, like critical micellar concentration (CMC), critical aggregation concentration (CAC), polymer saturation point (PSP), degree of ionization (β), and standard free energy of transfer ( \( \Delta G_{t}^{0} \) ), have been calculated. CAC values have been found to decrease with polymer concentration and increase with temperature. However, the PSP values increase with both polymer concentration and temperature for all surfactants. Similar parameters have also been calculated from surface tension data (CMC^σ, CAC^σ, PSP^σ) along with other parameters such as maximum surface excess concentration at the air/water interface ( \( \Gamma_{\hbox{max} } \) ), minimum area per molecule (A _min), and packing parameter (p). The CMC^σ, CAC^σ, and PSP^σ values are smaller than the corresponding CMC, CAC, and PSP values, but both show similar behaviour with temperature and concentration of polymer. Various parameters indicate that the presence of the aromatic ring in the head group of surfactant decreases its interaction with PEO, whereas the increased hydrophobicity in the tail leads to stronger interactions with PEO. Viscosity studies further supplement the conclusions drawn from the above results.