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International audience; (Z)- and (E)-iminoacetonitriles (NCCH═NH), two hydrogen cyanide dimers, are described as key compounds in prebiotic chemistry. Among the many possible dimers of HCN with covalent bonds, even the second on the scale of thermodynamic stability, methylenecyanamide (CH(2)═NCN), has been investigated little. We show that this compound can be isolated, is stable enough to give an adduct with a nucleophile or a diene, and can be easily generated under prebiotic conditions, highlighting a possible role in this medium. Comparison between isomers shows significant differences in formation and chemical reactivity.

In this work we seek to understand and to quantify the reactivity of benzofurazan derivatives toward secondary cyclic amines, like pyrrolidine, piperidine and morpholine, acting as nucleophile groups in SNAr reactions. For this aim, physico-chemical and structural descriptors were determined experimentally and theoretically using the DFT/B3LYP/6-31+ g (d,p) methodology. Thus, different 4-X-7-nitrobenzofurazans (X = OCH3, OC6H5 and Cl) and products corresponding to the electrophilic aromatic substitution by pyrrolidine, piperidine and morpholine, were investigated. Particularly, the HOMO and LUMO energy levels of the studied compounds, determined by Cyclic Voltammetry (CV) and DFT calculations, were used to evaluate the electrophilicity index (ω). The latter was exploited, according to Parr’s approach, to develop a relationship which rationalizes the kinetic data previously reported for the reactions of the 4-X-7-nitrobenzofurazans with nucleophiles cited above. Moreover, the Parr’s electrophilicity index (ω) of these benzofurazans determined in this work were combined with their electrophilicity parameters (E), reported in preceding papers, was found to predict the unknown electrophilicity parameters E of 4-piperidino, 4-morpholino and 4-pyrrolidino-7-nitrobenzofurazan. In addition, the relationship between the Parr’s electrophilicity index (ω) and Hammett constants σ, has been used as a good model to predict the electronic effect of the nucleophile groups. Finally, we will subsequently compare the electrophilicity index (ω) and the electrophilicity parameters (E) of these series of 7-X-4-nitrobenzofurazans with the calculated dipole moment (μ) in order to elucidate general relationships between E, ω and μ.

Kinetics studies for the coupling reactions of the 3-X-thiophene 1a-c (X = CH3, H and Br) with the electrophiles 2a and 3a-c have been investigated in acetonitrile at 20°C The second-order rate constants have been employed to determine the nucleophilicity parameters N and s of the thiophene 1 according the Mayr equation log k (20°C) = s (E + N). The nucleophilic-specific parameters N and s quantified in this work have been derived and compared with the reactivity of other C nucleophiles. Based on the linear correlations log k1 = f(E) and log k1 = f(σp+), we have shown that the mechanism of interactions occurs by a unique process: electrophilic heteroaromatic substitution of an α-carbon position of substituted 3-X-thiophenes 1 known hyperortho correlation.

A facile synthetic method for N-alkylated substituted benzochalcogenadiazoles is described. When treated with Meerwein salt, the 4-nitrobenzochalcogenadiazoles have undergone an N-alkylation to afford the expected salts as a mixture of two N1/N3 isomers in toluene. The regioselectivity of the alkylation reaction was then confirmed by spectroscopic data as well as theoretical calculations.

For the first time, p-nitro-benzylidenemalononitrile was integrated in Poly(9-vinylcarbazole) (PVK) P-type polymer. The UV–Vis spectra showed an enhancement of the optical response of the composite related to a π–π interaction that occurs between conjugated systems of carbazole groups and NO2BMN molecules. The Photoluminescence curves showed a significant quenching that is related to the charge transfer phenomenon occurring between donor and acceptor compounds. The electrical response revealed that the PVK: NO2BMN composite had a diode behavior. Thus, the electrical parameters improved upon the addition of NO2BMN. The capacitance exhibited Mott–Schottky behaviour, indicating the formation of a Schottky junction (band bending) at the PVK: NO2BMN/Al interface. The interface state density Nss and trap state’s time constant values τ of PVK and PVK: NO2BMN were [1.406 (1014 eV−1 m−2), 0.77 µs] and [1.321 (1014 eV−1 m−2), 0.10 µs], respectively. This result was compared to the literature and showed that the NO2BMN enhances the composite performance. From capacitance, the built-in potential and the minority charges concentrations were calculated for the composite. We found the values of Vbi = 2.6 V and NA = 3.49 (1016 cm−3).

Nonlinear optical (NLO) effects of organic materials are caused by delocalized electrons and large polarization in molecules. In the present work, theoretical study by using the Density Functional Theory (DFT) at B3LYP/6-311G(d,p) level of theory on three types of pyridine derivates 2,6-dimethoxy-3,5-dinitropyridine (M1), 2-methoxy-3-nitropyridine (M2) and 2-methoxy-5-nitropyridine (M3) is reported. The nuclear magnetic resonance (1H and 13C NMR) chemical shifts of the title compounds were calculated using the Gauge Independent Atomic Orbital (GIAO) method and compared to the observed results. Both infrared absorption and Raman are complementary to provide characteristic fundamental vibrations that are necessary for the identification of the molecular structures. Electronic properties such as frontier molecular orbital (HOMO, LUMO), ionization potential ( IP ad ) and electronic affinity ( EA ad ) were determined to get better insight into the molecular properties. Using the Time-Dependent Density Functional Theory (TD-DFT), electronic absorption spectra have been predicted and closely matching the experimental findings. The natural bonding orbital (NBO) calculations were performed in order to elucidate various second order interactions in between the filled and vacant orbitals which are a measure of the intermolecular as well as the delocalization within the molecule. In addition, we have demonstrated that these molecular systems have large first static hyperpolarizabilities and may have potential applications in the development of NLO materials.

The carbon-carbon cross-coupling of phenyl s-tetrazine (Tz) units at their ortho-phenyl positions allows the formation of constrained bis(tetrazines) with original tweezer structures. In these compounds, the face-to-face positioning of the central tetrazine cores is reinforced by π-stacking of the electron-poor nitrogen-containing heteroaromatic moieties. The resulting tetra-aromatic structure can be used as a weak coordinating ligand with cationic silver. This coordination generates a set of bis(tetrazine)-silver(I) coordination complexes tolerating a large variety of counter anions of various geometries, namely, PF6−, BF4−, SbF6−, ClO4−, NTf2−, and OTf−. These compounds were characterized in the solid state by single-crystal X-ray diffraction (XRD) and diffuse reflectance spectroscopy, and in solution by 1H-NMR, mass spectrometry, electroanalysis, and UV-visible absorption spectrophotometry. The X-ray crystal structure of complexes {[Ag(3)][PF6]}∞ (4) and {[Ag(3)][SbF6]}∞ (6), where 3 is 3,3′-[(1,1′-biphenyl)-2,2′-diyl]-6,6′-bis(phenyl)-1,2,4,5-tetrazine, revealed the formation of 1D polymeric chains, characterized by an evolution to a large opening of the original tweezer and a coordination of silver(I) via two chelating nitrogen atom and some C=C π-interactions. Electrochemical and UV spectroscopic properties of the original tweezer and of the corresponding silver complexes are reported and compared. 1H-NMR titrations with AgNTf2 allowed the determination of the stoichiometry and apparent stability of two solution species, namely [Ag(3)]+ and [Ag(3)2]2+, that formed in CDCl3/CD3OD 2:1 v/v mixtures.

The course of organic chemical reactions is efficiently modelled through the concepts of "electrophiles" and "nucleophiles" (meaning electron-seeking and nucleus-seeking reactive species). On the one hand, an advanced approach of the correlation of the nucleophilicity parameters

We have successfully synthesized and characterized a donor-bridge-acceptor type conjugated molecule. The absorption and photoluminescence spectra of NO2-benzylidenemalononitrile (NO2-BMN) thin films have been investigated. The NO2-BMN film shows an emission in the visible range, which makes it possible for optoelectronic application. The optical band gap was obtained by the Tauc method from the absorption spectra to be equal to 2.2eV. However the electrochemical gap calculated from cyclic voltammetry is 2.42 eV. Electrical properties of the ITO/NO2-BMN/Al structure was investigated by I-V characteristics. Diode parameters, such as the barrier height ϕb and the ideality factor n were calculated. The conduction is governed by space-charge-limited current (SCLC) mechanism. The effective hole mobility calculated is comparable to that of C60 and 2,7-distyrylcarbazole new molecule (≈10−5 cm2/V). The obtained results of the materials have promising to be applicable for various optoelectronic applications.

σ-complexation reactions of 2-N-(4′-X-pheny1)-4,6-dinitrobenzotriazole 1-oxides 1a (X = CH3) and 1e (X = CF3) with a series of C-nucleophiles, as reference, have been investigated kinetically in aqueous solution at 20 °C. The reactions are second-order and exhibit electrophilicity parameter E = -10.25 for 1a and E = -11.66 for 1e. Comparison with other derivative benzotriazoles 1a, 1c, 1d, and 1f–i reported in preceding papers is discussed, and it is shown that the E vs. pKa plot is nonlinear. In this context, geometries optimization of electrophiles 1a–i were performed at density functional theory (DFT) with the B3LYP hybrid functional and the 6–31 g(d,p) and 6–31 + g(d,p) basis sets, in acetonitrile, using the Gaussian 09 package, in order to clarify the negative deviations observed for benzotriazoles 1h and 1i. Thus, the origin of the nonlinear E vs. pKa plot was interpreted in terms of strong steric compression of the adjacent ortho-nitro and N-oxide functions. In addition, Parr's electrophilicity indices ω for these series of benzotriazoles 1a–i were calculated from the electronic chemical potential μ and the chemical hardness η and compared to experimental electrophilicity parameters E. More importantly, it has been shown that such theoretical and experimental electrophilicity scales are linearly and directly related to the correlation parameters of r2 > 0.97.

Kinetics of the nucleophilic aromatic substitution reactions of 7-L-4-nitrobenzofurazans 1 (1a: L = Cl and 1b: L = OCH3) and secondary cyclic amines (morpholine, piperidine, and pyrolidine) 2a–c have been measured in acetonitrile solution at 20°C. The derived values of second-order rate constants (k1) have been employed to determine the electrophilicity parameters E for both benzofurazans 1a and 1b according to the linear free enthalpy relationship: log k (20°C) = sN(E + N) (Eq. (1)). The second-order rate constants for reactions of benzofurazans 1 with a series of 4-X-substituted anilines 3a–d (X = OH, OCH3, CH3, and H) have also been measured in MeCN and found to agree within a factor of 0.14–50 with those calculated by Eq. (1) from the electrophilicity parameters E measured in this work and the known nucleophile-specific parameters N and sN of anilines 3. On the other hand, the reactions of these benzofurazans 1 with anilines 3 exhibit linear Bronsted-type plots with βnuc = 1.27 for 1a and 1.01 for 1b, which are considerably greater than those (0.57 for 1a and 0.62 for 1b) obtained with the secondary cyclic amines 2. These high values of βnuc have been interpreted in terms of a single electron transfer mechanism. Secondary evidence for the validity of this mechanism is provided by the agreement between the rate constants, k1, for substitution of benzofurazans 1 by the anilines 3 and their oxidation potentials E°.

The kinetics of the reactions of benzylidenecyanoacetates 1a–d (X = H, Me, OMe, and NMe2) with nitroalkyl anions 2a–c have been studied in aqueous solution at 20°C. The second-order rate constants are used to evaluate the electrophilicity parameter E of these series of Michael acceptors 1a–d according to the linear free enthalpy relationship log k (20°C) = sN (E + N). The measured E values were found to cover a domain of reactivity, ranging from −10.07 for the most reactive electrophile 1a (X = H) to −14.04 for the less electrophile 1d (X = NMe2). Mayr's approach was found to correctly predict the rate constants for the reactions of these series of olefins 1a–d with the hydroxide ion in water and 50% water–50% acetonitrile at 20°C. Analysis of the kinetic measurements using the Bronsted relationship shows that βnuc values remain remarkably constant for changes in the nature of the substituent X. A notable finding of this work is perhaps provided by the observed large changes in the electrophilicity parameter E on going from benzylidenecyanoacetates 1 to their analogues benzylidenemalonates 3 (ΔE ∼ 9.06–10.48), whereas the replacement of second CO2Et group by the CN group in 1 to give benzylidenemalononitriles 4 has little effect on electrophilic reactivity, i.e., ΔE ∼ 0.65–0.95. This abnormal pattern in the E values has been attributed to the resonance interaction and salvation effects. On the other hand, the effect of benzylidenecyanoacetate substituents on the electrophilic reactivity was examined quantitatively on the basis of the electrophilicity parameter E, leading to linear correlation of E with Hammett–Brown substituent constants (σp+). More importantly, the four electrophiles have comparable log ko values, which are located at a relatively low level, i.e., log ko ≤ 4–5, in the intrinsic reactivity scale.

Second-order rate constants (k1) for the σ-complexation of 4-nitrobenzofurazan 1 with four 4-X-substituted phenoxide anions 2a–2d (X = OCH3, CH3, H and Cl) were measured in aqueous solution at 20 °C. Using this series of phenoxide anions as a reference, the electrophilicity parameter (E) of this electrophile 1 has been evaluated according to Mayr’s approach. With the E value of –9.42, Mayr’s equation was found to correctly predict the rate constants for the reactions of 1 with hydroxide ion in H2O and a 1:1 ratio of H2O to CH3CN. However, the large βnuc value of 1.12 obtained in the present work is clearly consistent with a single electron transfer (SET) mechanism.

The nucleophilic addition reactions of N1-methyl-4-nitro-2,1,3-benzoselenadiazolium tetrafluoroborate 1 with aliphatic amines 2a–c (diethylamine 2a, dipropylamine 2b, and allylamine 2c) have been kinetically studied by UV–vis spectroscopy in acetonitrile solution at 20°C. The kinetic data have been analyzed, using the Mayr equation, allowing the quantification of the electrophilicity parameter (E) value of benzoselenadiazolium cation 1 (E = −14.72). The reliability of parameter E has been reasonably verified by comparison of calculated and experimental second-order rate constants for the reactions of cation 1 with other amines 2d–f (pyrrolidine 2d, piperidine 2e, and morpholine 2f) under the same conditions as those of the amines 2a–c. A linear Bronsted plot (R2 = 0.9945) with a βnuc value of 0.55 has been obtained for the reactions of 1 with the secondary amines employed in the present work. Interestingly, satisfactory correlation between the log values of measured and calculated rate constants with a slope very close to unity has been obtained and discussed.

International audience; Through the linear free energy relationship log k=sN (N + E), the electrophilicity parameters E of 4-nitrobenzochalcogenadiazoles 1 a and 1 b have been determined, at 20 °C, by kinetic investigations of their electrophilic addition reactions to a series of nitroalkyl anions 2 a-c in aqueous solution. The derived E-parameters of electrophiles 1 a (E=-12.80) and 1 b (E=-11.46) have been integrated into the electrophilicity scale established by Mayr. Interestingly the less activated compound (1 a) has an E value which is practically the same as that of the 1,3,5-trinitrobenzene (E=-13.19), the common reference aromatic electrophile. Mayr's approach was found to predict the rate constants for σ-complexation reactions of our electrophiles 1 a and 1 b with aniline and 4-chloroaniline in acetonitrile with a factor of 10−36. Good linear correlation (r2=0.9979) between the electrophilicity parameters E of 4,6-dinitrobenzochalcogenadiazoles 3 a-c and E values of their analogously 4-nitrobenzochalcogenadiazoles 1 a-c has been found and analysed. Furthermore, effect of basicity of nitronate anions 2 a-c on their nucleophilic reactivity has also been examined quantitatively on the basis of kinetic data. Imbalance effect is suggested to be responsible for the finding of an inequality between the Brønsted αelec and βnuc values.

The SNAr mechanism invoked in this work concerned the substitution reaction of the methoxy group by a secondary amine on the 2-methoxy-5-nitrothiophene and 2-methoxy-3,5-dinitrothiophene molecules. We performed theoretical DFT and TD-DFT calculations. It was examined by theoretical DFT calculations. The hypothesis of a zwitterion formation during the kinetically determining step has been confirmed. However, our calculations have shown that the structure of this reaction intermediate is much more diffuse than commonly accepted. Its geometry can be described as one situation in which the nitrogen of the nucleophilic entity is not totally bound to the carbon, whereas the oxygen of the leaving group prepares to be separated from the substrate. The transition state corresponding to the formation of the zwitterion has a barrier of 17.78 kcal mol−1 in methanol. Three pathways have been studied to describe the second step, leading to the formation of methanol or methoxyammonium. The most probable pathway uses, in a first sequence, a second amine molecule to convert the zwitterion, a dipolar compound, into a hydrogen-bonding association of a carbanion located on the carbon C5 carrying the nitro group and an ammonium with a weak activation barrier of 2.25 kcal mol−1. The electron density supplement provided by the nucleophile is stored at the oxygen atoms of the 5-nitro group in position α of the sulfur atom. The presence of a second nitro group in position β modifies the structure of this carbanion by locating the negative charge on the carbon C3 carrying the second nitro. To visualize the reaction mechanism, we propose an innovative technique called reactive internal reaction coordinate that traces the reaction pathway in a 3D figure as a variation of the energy according to the most active internal coordinates in the transition-state zone of influence.

Metal-catalysed ortho-directed C–H functionalization usually faces selectivity issues in the competition between mono- and disubstitution processes. We report herein the ruthenium-catalysed N-directed C–H monoarylation of arylpyrazoles with a selectivity of up to 96% or that generally reaches values above 80%. This selectivity is an effect of solvent-free conditions associated with sulfonate reagents, in the absence of frequently used acidic additives.

The solution-processable small organic molecules have provoked the interest for their applications in cost-effective optoelectronic devices. This work presents the incorporation of the small organic molecules of 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) into the MEH-PPV polymer matrix to enhance the performance of charge transport. The absorption and photoluminescence spectra were used to investigate the optical properties of the composite films. An optimal weight ratio of (1:0.5) of MEH-PPV:NBD-Cl is found to achieve the best efficiency of charge transfer. For the same composition, the device based on ITO/MEH-PPV:NBD-Cl/Al shows an improvement in current levels and reduction in threshold voltage. Additionally, by fitting the experimental impedance spectroscopy data, informations about the resistances and mobilities were extracted. The effective charge mobility are 1.62 × 10 - 3 cm² V−1s−1.

Kinetics of the reactions of 7-Imidazolium-4-nitrobenzofurazan 1a and 7-phenoxy-4-nitrobenzofurazan 1b with secondary amines 2a-c were studied spectrophotometrically in acetonitrile at 20 °C. The second-order rate constants have been used to evaluate the electrophilicity parameters E of 1a and 1b according to the linear free energy relationship log k (20 °C) = s (N + E). The theoretical electrophilic reactivity of the 7-phenoxy-4-nitrobenzofurazan 1a and 7-Imidazolium-4-nitrobenzofurazan 1b and two other nitrobenzofurazans 1c (L = OCH3) and 1d (L = Cl) have been studied by Density Functional Theory (DFT/B3LYP: Becke, 3-parameter, Lee- Yang-Parr) and the 6–311g(d,p) basis set implemented in Gaussian 09W Software. The derived electronic chemical potential (μ) and the corresponding chemical hardness (η) parameters have been used to calculate the global electrophilicity index (ω) of these series of electrophiles defined by the relationship ω = μ2/η. A good correlation between the calculated ω values and their experimentally observed electrophilic reactivities (i.e., Mayr’s electrophilicities E) is found and discussed.

International audience

The kinetics of the coupling of N1-methyl-4-nitro-2,1,3 benzothiadiazolium tetrafluoroborate 1 with a series of 4-X-substituted anilines 2a–f (X = OH, OMe, Me, H, Cl, and CN) have been investigated in acetonitrile at 20°C. The second-order rate constants result in a nonlinear Bronsted-type plot. The Hammett plot is also nonlinear, whereas the Yukawa–Tsuno plot exhibits an excellent linear correlation with ρ = –1.62 and r = 1.44. The large Bronsted (βnuc = 1.24) and Hammett (ρ = –5.16) values suggest that the reactions proceed trough a single electron transfer mechanism. The finding of satisfactory correlation between the log k1 of the reactions and the oxidation potentials (E°) of anilines 2a–d supports this mechanism. On the other hand, electrophilicity parameter E of benzothiadiazolium cation 1 as defined by the correlation log k20°C = s(E + N) has been determined and compared with the electrophilic reactivities of a large variety of electrophiles.

International audience; The biosorption potential of Zn(II) from aqueous solutions using activated sludge biomass was investigated. Optimum biosorption conditions were determined with respect to pH, adsorbent dose, contact time and temperature. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models were applied to the equilibrium data. The maximum Zn(II) sorption capacity of activated sludge was found to be 76.92mgg(-1) at pH 6, biomass concentration 2gL(-1), contact time 30min and temperature 20 degrees C. The calculated mean biosorption energy (9.82kJmol(-1)) using D-R model indicated that the biosorption of Zn(II) on the biomass was induced by chemical ion exchange.

Second-order rate constants for the reactions of 2-aryl-4,6-dinitrobenzotriazole 1-oxides 1a-d with some 4-X-substituted phenoxide ions 2a-d (X = OCH3, H, Cl, and CN) have been measured in aqueous solution at 20°C. The pKa values for the σ-complexation processes of a series of benzotriazole 1a-d measured in water have been used to determine their electrophilicity parameters E according to the correlation E = –3.20 – 0.662 pKa (F. Terrier, S. Lakhdar, T. Boubaker, and R. Goumont, J Org Chem, 2005, 70, 6242–6253). For these reactions, plots of log k versus the electrophilicity parameters E of the benzotriazoles 1a-d were linear, allowing to derive the nucleophilicity parameters N and s for phenoxide ions as defined by the Mayr equation log k1 (20°C) = s (E + N) (H. Mayr, M. Patz. Angew Chem, Int Ed Engl 1994, 33, 938–957). The N values are found to cover a range of nucleophilicity from 6.85 to 10.22, going from 4-cyanophenoxide 2d for the least reactive ion to 4-methoxyphenoxide 2a for the most reactive nucleophile. Good linear correlations were found between the nucleophilicity parameters N of phenoxide ions 2a-d and the pKa values of their conjugate acids (N = –3.05 + 1.25 pKa) and the constants of the substituents X (N = 9.21 – 2.51).

The kinetics of σ complexation of unsymmetrical 2-nitro-4,6-bis(trifluoromethylsulfonyl)anisole (1e) has been investigated over a large pH range of 2.7–15.68 in methanol. Two competitive σ complexation processes have been identified that lead, respectively, to the formation of the 1,3- and 1,1-adducts 2e and 3e of 1e. No evidence for nucleophilic addition at the unsubstituted 5-position para to the nitro group of 1e to afford the 1,5-dimethoxy adduct 4e could be obtained. The observed regioselectivity supports the view derived from previous investigations that a SO2CF3 group exerts a much stronger electron-withdrawing effect than a NO2 group, both in the ortho and para positions of a reactive centre in an aromatic ring. In accord with this conclusion, the 1,1-dimethoxy adduct 3e is found to be 102-fold less stable than the tris-SO2CF3 analogue 3a but ten times more stable than the 1,1-dimethoxy adduct 3b of 4-nitro-2,6-bis(trifluoromethylsulfonyl)anisole (1b). However, a most significant result is the finding that the solvent contribution to the formation of 3e is not negligible in the pH range of 9–10. With a pKaMeOH value of 9.42, the electrophilic reactivity of the parent triflone 1e is clearly located in the region of extremely high electrophilicity defined for σ complexation and SNAr substitutions in methanol (pKaMeOH ≤ 9–10). This work adds to the recognition that the activating effect of a SO2CF3 group is in general much greater than that of a NO2 group when bonded to an aromatic or heteroaromatic ring. A return to the origin of the exceptional electron-transmission capability of the SO2CF3 group is helpful to predict reactivity.

A kinetic study is reported for reactions of 2-methoxy-3-X-5-nitrothiophenes 1a–d (X = SO2CH3, CO2CH3, CONH2, H) with piperidine in different solvents at 20°C. It is shown that the reactions take place through a SNAr mechanism with the initial nucleophilic addition step being rate limiting. The satisfactory Hammett correlations (log k1 vs. σ) obtained in the present system confirms that a 3-X substituent exerts an effect on the 2-position of the same type as that exerted from the 5-position. The second-order rate constants associated with these reactions are employed to determine the electrophilicity parameters E of the thiophenes 1a–d according to the relationship log k (20°C) = s(E + N) (Angew. Chem., Int. Ed. Engl. 1994, 33, 938–957). The E values of 1a–d are found to cover a range from −21.33 to −17.18, going from 1d, the least reactive, to 1a, the most reactive thiophene. Interestingly, a linear correlation (r2 = 0.9910) between the electrophilicity parameters E determined in this work and the Hammett's σ constants values has been observed and discussed. On the other hand, we have found that the reported rate constants of some thiophenes 1 complexation by the methoxide ion in methanol are 3.5–73.5 times higher than predicted by Mayr's approach.

The biosorption characteristics of copper(II) ions using Posidonia oceanica biomass were investigated. Experimental parameters affecting the biosorption process such as pH level, contact time, biosorbent dosage and temperature were studied. The equilibrium data were applied to the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. The Langmuir model fitted very well the equilibrium data, and the maximum uptake of Cu(II) by Posidonia oceanica was found to be 76.92 mg/g. The mean free energy E (10.78 kJ/mol) from the D-R isotherm indicated a chemical ion-exchange mechanism. Kinetic results showed that the pseudo-second-order kinetic model was well fitted to the experimental data. Thermodynamic parameters depicted the exothermic nature of biosorption and the process was feasible and spontaneous. The results of FTIR (Fourier-transform infrared spectroscopy) revealed that carboxyl, amine, and hydroxyl groups on the biomass surface were involved in the biosorption of Cu(II) ions.

This paper presents the characteristics of Cd(II) biosorption from aqueous solution using the brown alga (Dictyota dichotoma) as a function of pH, biomass dosage, contact time and temperature. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were applied to describe the biosorption isotherms of Cd(II) by D. dichotoma biomass. The monolayer biosorption capacity of D. dichotoma biomass for Cd(II) ions was found to be 75 mg/g. The mean free energy calculated from D–R isotherm indicated that the biosorption of Cd(II) onto D. dichotoma macroalga took place by chemisorption. Kinetic evaluation of the experimental data showed that the biosorption process followed pseudo-second-order model.The calculated thermodynamic parameters Δ, Δ and Δ, showed that the biosorption of Cd(II) onto D. dichotoma biomass was feasible, spontaneous and exothermic under examined conditions. X-ray photoelectron spectroscopy (XPS) and FT-IR analysis of D. dichotoma revealed the chelating character of the ion coordinat...

Kinetic studies for the Michael-type reactions of ethyl-3-(4′-N,N-dimethylaminophenyl)-2-(nonafluorobutane)sulfonylpro-penoate 1 with 4-X-substituted anilines 2a–e (X = OCH3, CH3, H, F, and Cl) have been investigated in acetonitrile at 20°C. A quadratic dependence of the pseudo–first-order rate constants (kobsd) versus [2a–e] has been observed and has been interpreted in terms of a dimer nucleophile mechanism. The finding of a relatively large negative ρ value (−3.09) for the Hammett plot suggests that the intermediate (I±) is highly zwitterionic in nature. A linear correlation (r2 = 0.9989) between the Hammett's substituent constants σ and nucleophilicity parameters N of 4-X-substituted anilines in acetonitrile has been observed. The electrophilicity parameters E of the olefin 1 is evaluated, using the correlations σ versus N and log k versus σ and compared with the electrophilicities of analogously Michael acceptors.

A modular indole synthesis based on an intramolecular 5-endo-dig carbocupration starting from readily available N-aryl-ynamides is reported. A variety of ynamides are converted to indoles in moderate to good yields and with varying substitution pattern on the indole ring. This further extends the synthetic utility of ynamides in organic synthesis and provides additional insights on the use of intramolecular carbometalation reactions.