Solvent and substituent effects on spectroscopical changes of some diazoaminobenzene derivatives

A series of diazoaminobenzene derivatives (seven) in which the substituents have a wide range of electronic characters are set out to understand the involvement of the substituent identity in controlling the changes in their electronic absorption spectra. The interactions between the diazoamino group and the different groups account for some spectral shifts. The UV-vis spectrum of each compound is measured in several solvents with wide variations of solvent polarity parameters to examine the role of the chemistry of the solvent in these spectroscopical changes. The electronic transitions are assigned and the solvent induced spectral shifts are analyzed in relation to the different solute-solvent interaction mechanisms using computational chemistry. The regression analysis is applied for correlating the different parameters. The results help to assign the solute-solvent interactions and the solvatochromic potential of the investigated compounds. It is concluded that the electronic character of the substituent and the chemical nature of the solvent are the major factors for the observed solvatochromism.     

Controlling submicron-particle template morphology: effect of solvent chemistry

Porous solids were obtained from self-assembled deposits of silica particles used as templates to form 3-D porous membranes. The effect of the solvent chemistry on the morphology of the deposits was investigated. The parameters of interest are surface tension and ionic strength of the solvent, as they impact electrostatic and capillary interactions. Deposits of particles of different sizes were obtained from a variety of conditions. The deposits were imaged by SEM and showed distinctive structures for each of the solvent chemistries. The phenomenon is qualitatively consistent with DLVO theory and calculations of capillary interaction energy as developed by Kralchevsky and co-workers.     

A comprehensive study of the solvent effects on the cycloaddition reaction of diethyl azodicarboxylate and ethyl vinyl ether: Efficient implementation of QM and TD‐DFT study

In this work, quantum chemistry calculations performed to study the kinetics and thermodynamic parameters of [2+2] cycloaddition reaction of diethyl azodicarboxylate and ethyl vinyl ether in eighty‐three solvents and gas phase. The solvent effect on the reaction path and electron density of the C2? N6 critical bond as the reaction coordinate at the TS was investigated. Calculated rate constants in various solvents showed that increase in the activation dipole moment accelerates the reaction. Based on the time‐dependent studies, using a conductor like polarizable continuum model solvation model, the solvent effects on the excitation energies of the reactants and transition states (TSs) and the corresponding chemical shifts were analyzed. Finally, some correlations between the rate constant and quantum reactivity indices such as electrophilicity index, chemical hardness, and electronic chemical potential were investigated. © 2014 Wiley Periodicals, Inc.     

Structure of the HOOO radical in liquid water: a theoretical study.

The HOOO radical is supposed to play a role in ozone chemistry, both in the gas phase and aqueous media. We discuss the influence of the solvent on the electronic and geometrical structure of this radical using density functional and high-level ab initio calculations together with continuum, discrete, and discrete-continuum solvent models. Solute-solvent electrostatic interactions are shown to be fundamental, and lead to a noticeable stabilization of the radical, which should adopt a trans conformation in aqueous media. In fact, no energy minimum for the cis conformation is predicted in these conditions.     

Sol-Gel Synthesis of Potassium Titanyl Phosphate: Solution Chemistry and Gelation

The solution chemistry and aggregation mechanisms involved in sol-gel synthesis of potassium titanyl phosphate (KTP) are studied in detail. The chemistry of the metal precursors are shown to be critical for the formation of the desired KTP phase. The precursor solution as well as some preparation intermediates were studied by several spectroscopic methods to determine the structure of the organometallic species present in these solutions. The structural evolution taking place in the solution after hydrolysis was studied using photon correlation spectroscopy and small angle X-ray scattering techniques. The influence on the gelation of several preparation parameters such as, the precursors chemistry, the mixing order of the metal alkoxides, the solvent/KTP ratio and the water/KTP molar ratio was also examined.     

Treasures from the Free Radical Renaissance Period--miscellaneous hexenyl radical kinetic data

Rate constant data and Arrhenius parameters have been determined for a series of substituted hexenyl radicals of differing electronic and steric demand. Electron-withdrawing groups (CF(3), CO(2)Et) directly attached to the radical centre slightly accelerate 5-exo ring-closure (k(cis) + k(trans) ～ 2.1 × 10(5) s(-1) at 25°) relative to donating groups (OMe; 1.6 × 10(5) s(-1) at 25°). Sterically demanding groups (tert-Bu), as expected, slow the cyclization process (1 × 10(5) s(-1)). These observations are consistent with subtle changes in activation energy for 5-exo ring-closure. Interestingly, the nature of the solvent would appear to have a significant influence on this chemistry with the cis/trans stereoselectivity sometimes improved as the solvent polarity is increased. Except for the system containing the CF(3) (electron-withdrawing) group which displays an increase in the cyclization/capture rate constant (k(c)/k(H)), a general decrease in the k(c)/k(H) ratio as solvent polarity is increased is noted; these changes have been speculated to arise mainly from changes in k(H) in the various solvents employed.     

Solvent effects in ionic liquids: empirical linear energy-density relationships

Multiparameter linear energy-density relationships to model solvent effects in room temperature ionic liquids (RTILs) are introduced and tested. The model incorporates two solvent dependent and two specific solute-solvent parameters represented by a set of electronic indexes derived from the conceptual density functional theory. The specific solute-solvent interactions are described in terms of the electronic chemical potential for proton migration between the anion or cation and the transition state structure of a specific reaction. These indexes provide a quantitative estimation of the hydrogen bond (HB) acceptor basicity and the hydrogen bond donor acidity of the ionic solvent, respectively. A sound quantitative scale of HB strength is thereby obtained. The solvent dependent contributions are described by the global electrophilicity of the cation and nucleophilicity of the anion forming the ionic liquid. The model is illustrated for the kinetics of cycloaddition of cyclopentadiene towards acrolein. In general, cation HB acidity outweighs the remaining parameters for this reaction.     

Cyclic voltammetric studies into the reduction of a series of tris(1,3-diketonato)iron(III) compounds in dichloromethane and dimethylsulphoxide

A series of seven tris(1,3-diketonato)iron(III) chelates were prepared and studied using cyclic voltammetry in dichloromethane and dimethylsulphoxide. In the former solvent only a single reduction wave is observed and is assigned to the Fe(III)-Fe(II) couple. Despite the metal-based redox chemistry the formal potential is strongly influenced by the substituent groups on the chelating ligands and can be linearly correlated with the sum of the Taft inductive parameters for these substituents. In dimethylsulphoxide the reduced monoanion [Fe(1,3-diketonate)₃]⁻ undergoes a following chemical reaction which is interpreted as the extrusion of one 1,3-diketonate ligand. That reaction is an equilibrium and the position of the equilibrium is observed to depend upon the electronic effect of the substituent groups on the chelating ligands. For the strongly withdrawing trifluoroacetylacetonate ligand the dissociation of that ligand is essentially quantitative.     

Reductive Elimination or C−C Bond Activation with Model Ni,Pd, Pt Complexes? A High-Accuracy Comparative Computational Analysis of Reactivity

The development of Pd- and Ni-catalyzed reactions for C−C bond formation is one of the primary driving forces in modern organic synthesis and the fine chemical industry. However, understanding the role of conformational mobility in reaction mechanisms is a long-standing challenge. We highlight the effect of a multirotamer (multiconformer) system on the effective Gibbs free energy of activation in the key C−C coupling process and promote the use of a simplified version of multiconformer transition state theory that is straightforward to apply. Multivariate regression helped to quantitatively map the effect of coupled organic substituents (their structural and electronic parameters), as well as to determine the relative activity of metals. We provide computational evidence for solvent control of the equilibrium in RE/C−C-bond activation for some model complexes. We also demonstrate that Ni complexes, being unique in the catalysis of sp³-sp³ couplings, can be more challenging for machine learning and computational chemistry. The modeling was performed at an exceptionally high level, DLPNO-CCSD(T)/CBS//RIJCOSX-PBE0-D4/def2-TZVP. The Conclusions section contains an infographic summarizing the key findings related to the fields of cross-coupling catalysis, machine learning in catalysis, and computational chemistry.     

Kinetics of 1,3-dipolar cycloaddition on the surfaces of Au nanoparticles

Triazole formation via 1,3-dipolar cycloaddition, or "click" chemistry, is a powerful synthetic method for incorporating chemical functionality onto the surfaces of Au nanoparticles. To investigate the factors that govern azide/alkyne reactivity at particle surfaces, we measured the general kinetic trends for the uncatalyzed reaction using FTIR spectroscopy. This study examines the roles of ligand length, electronic substitution of the alkyne species, and solvent on the reaction under pseudo-first-order conditions. The conversion of azide to triazole is found to depend more strongly on the relative surface coverage of azide terminated alkanethiol than on the ligand length and solvent.     

Molecular orbital calculations on solvents and other small molecules: Correlation between electronic and molecular properties ν, αMOL, π*, and β.

Molecular orbital calculation by the MINDO/3 method are reported for 50 compounds used as solvents in chemical reactions. Relationships between various parameters of electronic structure and molecular properties such as dipole moment, polarizability and Taft solvent parameters are presented. Comparison between experimental values of π* and calculated values is given.     

Predicting the solution morphology of a sulfonated pentablock copolymer in binary solvent mixtures

The solution morphologies of a midblock-sulfonated pentablock copolymer in miscible polar/nonpolar solvent blends were characterized as a function of solvent composition and polymer concentration using small angle X-ray scattering. Three distinct solution morphologies are observed upon changing the composition of the solvent blend. At low weight fractions of polar solvent, spherical, sulfonated-core micelles are observed, while spherical, sulfonated-corona (inverted) micelles are observed at high weight fractions of polar solvent. Polymer solution scattering is observed at intermediate concentrations of polar solvent. Additionally, the characteristic dimensions of the sulfonated-core micelles were found to change strongly upon variation of the solvent blend composition, indicating that these solutions—and correspondingly the morphology and properties of polymer membranes into which they are cast—can be tuned through simple variations in the solvent blend chemistry. We demonstrate that the solution morphologies and the characteristic micelle dimensions of these complex pentablock copolymer/binary solvent blends can be reliably predicted by considering the relative interactions of each polymer block and the solvent blend using the Hansen solubility parameters. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 254–262     

Solvatochromic behaviours and structure–spectra relationships of 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes

Comprehensive electronic absorption spectra of a new dye series, 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes have been investigated in solvents of varying polarities. The solvent dependent UV–vis spectral shifts were analysed using some solvent physical parameters such as refractive index, dielectric function, hydrogen bonding acceptor ability, orientation of polarization and others. The observed spectral shifts were correlated with different solute–solvent interaction mechanisms using simple and multiple linear regression analyses. The results of the curve fitting coefficients enabled us to classify the various interactions of solvents with the dyes and relate the solvatochromic behaviours to the substituent effects on the dye molecules. Charge-transfer complexation occurring between one of the congeners and N,N′-dimethylformamide was extensively studied and discovered to be both concentration- and temperature-dependent.The electronic character and the chemical nature of the solvents as well as the chemical nature of the other substituents, apart from the common hydroxyl group, are important factors for the observed solvatochromic properties of the 4-carboxyl-2, 6-dinitrophenylazohydroxynaphthalenes.     

Relation between molecular structure and spectral characteristics of some chelating mono-azo dyes based on o-hydroxy aryl aldehydes and carboxylic acids

The electronic absorption spectra of some chelating mono-azo compounds have been studied in some organic solvents of varying polarities. The u.v. bands in ethanol and cyclohexane are assigned in the light of electronic transitions. The effect of microscopic and macroscopic solvent polarity parameters are also discussed. The i.r. spectra of the solid compounds as KBr discs as well as the ¹H NMR spectra have also been assigned and discussed in relation to molecular structure. The azo ⇌ hydrazone tautomerism in some of these compounds is assured. The study indicated that the colour of the materials depends on the polarity and the formation of intermolecular H-bonds with the solvent molecules.     

CHIH-DFT determination of the molecular structure and infrared and ultraviolet spectra of gamma-solanine

Glycoalkaloids are toxic secondary plant metabolites found in potatoes, tomatoes, and eggplants and they are considered potential precursors of steroids for applications in bionanotechnology. In this work, we make use of a new model chemistry within density functional theory, which is called CHIH-DFT, to calculate the molecular structure of gamma-solanine, as well to predict its infrared (IR) and ultraviolet (UV-vis) spectra, and some other electronic parameters.     

Cl+CH4反应的电子相关、基组与化学反应性

Using the results of quantum chemistry, thermodynamic and kinetic calculations for this experimentally well studied reaction has been carried out. The adaptability of the computational results of diffrent quantum chemistry schemes (considering electronic correlation or not, and basis size) has been analyzed for the chemical reactivities (thermodynamic functions and kinetic parameters). The calculated results are in good agreement with the experimental ones using the larger basis set and considering electronic correlation, but are bad on the contrary. In addition, a set of exact thermodynamic functions and kinetic parameters has been given.     

Thermodynamics of Cobalt(III) Schiff base complexes in various solvents

The electronic and steric effects of some Schiff bases and the solvent on the thermodynamic parameters of the pentacoordinate Co(III) Schiff base complexes were studied. The formation constants and the thermodynamic parameters were measured spectrophotometrically for 1:1 adduct formation of the complexes as acceptors with tributylphosphine (PBu₃) as donor, in some solvents (acetonitrile, tetrahydrofuran, butanol, ethanol and N,N-dimethylformamide) in constant ionic strength (I = 0.01 M, sodium perchlorate) and at various temperatures. The trend of the reactivity of the pentacoordinate cobalt(III) Schiff base complexes toward tributylphosphine according to the solvent is as follows: acetonitrile > tetrahydrofuran > butanol > ethanol > N,N-dimethylformamide. The trend of the reactivity of pentacoordinate cobalt(III) Schiff base complexes toward the donor in a given solvent according to the equatorial Schiff base is as follows: BBE > BAE > Salen.     

Synthesis of diastereomerically and enantiomerically pure 2,3-disubstituted tetrahydrofurans using a sulfoxonium ylide

Nucleophilic substitution reactions of 2,3-epoxy alcohols, easily prepared via Sharpless asymmetric epoxidation chemistry, offer access to a wide variety of enantiomerically pure compounds. In this communication, we describe the use of a Payne rearrangement to control regioselectivity in the ring-opening of a series of 2,3-epoxy alcohols with dimethylsulfoxonium methylide to yield diastereomerically and/or enantiomerically pure disubstituted tetrahydrofuran rings. The factors influencing the success and substitution pattern of the THF ring products are discussed, including steric, electronic, and solvent effects.