Intermolecular interactions in dioxane-water solutions of substituted coumarins according to ultrasonic data

Density, ultrasonic velocity of pure dioxane (Dx) and ligands, 4,6-dimethyl-7-hydroxycoumarin (L₁), 6-ethyl-7-hydroxy-4-methylcoumarin (L₂), and 3-chloro-7-hydroxy-4-methylcoumarin (L₃) in different percent of Dx-water mixture have been investigated at 303.15 K. Acoustical parameters such as adiabatic compressibility (β), intermolecular free length (L _f ), acoustical impedance (Z), relative association (R _A ), apparent molar compressibility (Φ_β), and apparent molar volume (Φ _V ) have also been evaluated from the experimental data of density and ultrasonic velocity. An excellent correlation between a given parameters is observed at all percent of dioxane-water and the result suggests nature of intermolecular interactions between the components.     

State of water in inverse micelles of Aerosol OT,according to IR spectroscopic data

Leningrad State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 4, pp. 81–85, July–August, 1991.     

Intermolecular interactions in the system of equilibrium catalytic transesterification of esters 2. Reaction of boron and arsenic butoxides with alcohols based on IR spectroscopic data

The reaction of alcohols ROH (R=Me, n-Bu, n-C₇H₁₅) with B(OBu)₃ and As(OBu)₃ in binary mixtures and in solutions in CCl₄ was investigated by IR spectroscopy. B(OBu)₃ forms equilibrium associates of two types with n-BuOH. Only one type of H bond is observed in a dilute solution of n-BuOH in As(_OBu)₃, but the donor sites in As(_OBu)₃ (As or O atoms) which participate in its formation were not established. The equilibrium constants of the reaction of exchange of butoxyl radicals in X(OBu)₃ (X=B, As) with MeOH and n-C₇H₁₅OH were measured and at 20°C were, respectively, equal to 0.11 and 0.06 for B_{OBu 3} and 0.67 and 0.44 for As_{OBu 3}.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 377–381, February, 1991.     

Study of intermolecular interactions in a system for equilibrium catalytic transesterification of esters. 1. Reaction of boron,titanium, and arsenic butoxides with esters according to IR fourier spectroscopic data

IR spectroscopy was used to study solutions of esters of PhCOOR (R=Me, Bu, C₇H₁₅, (CH₂)₂OBu) in B(OBu)₃, Ti(OBu)₄, and As(OBu)₃ and in mixtures of the latter with CCl₄ and hexane. It is shown that weak complexes form between the ester molecules and B(OBu)₃ and Ti(OBu)₄, As(OBu)₃ behaves with respect to the esters as a nonpolar solvent. Intermolecular interaction of the esters with butoxides occurs at the alkoxide oxygen in the ester. A mechanism of the exchange of the alkoxyl radical in the reaction of Ti(OBu)₄ with PhCOOMe is proposed on the basis of kinetic measurements.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1991–1995, September, 1990.     

Isomerism of 5-arylfurfural oximes (according to PMR spectroscopic data)

The stereochemistry of 5-arylfurfurals and their O-acetyl derivatives was studied by PMR spectroscopy. The configurations of each of the isomers were determined for the oximes of p-bromo- and p-chlorophenylfurfurals, which were isolated as two geometrical isomers, and also for their O-acetyl derivatives. The anti and syn configurations were established for the oximes of phenylfurfural and p-nitrophenylfurfural, respectively, which were obtained as single isomers. Conclusions regarding the preferred conformation of the side chain relative to the plane of the furan ring in all of the investigated isomers were drawn on the basis of an analysis of the of the long-range spin-spin coupling constants ( \({\text{J}}_{{\text{H}}_{\text{0}} {\text{H}}_{\text{4}} } \) ).     

Characteristics of the complexing of chitosan with sodium dodecyl sulfate,according to IR spectroscopy data and quantum-chemical calculations

The complexing of protonated chitosan with dodecyl sulfate ions in water solutions is studied using IR spectroscopy data and quantum-chemical calculations. It is established that the electrostatic interaction between the protonated amino groups of chitosan and dodecyl sulfate ions is apparent in the IR spectrum as a band at 833 cm^?1. The need to consider the effect the solvent has on the formation of hydrogen-bound ion pairs [CTS⁺ ? C₁₂H₂₅O₃^-] is shown via a quantum-chemical simulation of the equilibrium geometry and the energy characteristics of complexing and hydration.     

Conformation of monobenzyl ethers of piperidyl-containing acetylenic glycols,according to13C NMR spectroscopic data

In the¹³C NMR spectra of individual ()- and ()-epimers (through the C₄ carbon atom of the six-membered ring) of monobenzyl ethers of piperidyl-containing acetylenic glycols, it has been found that the chemical shifts of the epimers differ by as much as 3 ppm for the C₂, C₄, and C₆ carbon atoms. The most probable conformations of the epimers are suggested, including intramolecular hydrogen bonds between the proton of the OH group and the unshared electron pair of the nitrogen.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2780–2785, December, 1991.     

IR study of ion-molecular interactions in the system methanesulfonic acid-ethyl acetate

The complex formation in the methanesulfonic acid (MSA)—ethyl acetate (EA) system was studied by Multiple Attenuated Total Reflection (MATR) IR spectroscopy at 30°C. In solutions with excess EA, neither protonation of a base nor formation of complexes with a strong symmetrical H bond was observed. Molecular complexes EA·MSA are found in these solutions. Complexes formed by the strong symmetric H bond are observed in the system when the MSA content exceeds 50 mol.% Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2. pp. 292–294, February, 2000.     

Ion-molecular interactions and the equilibrium composition in the HCl-1-methyl-2-pyrrolidone-1,1,2,2-tetrachloroethane system according to IR spectroscopy data

Multiple Attenuated Total Reflectance (MATR) IR spectra of solutions of HCl in 1-methyl-2-pyrrolidone (N-MP) (0–43.4 % HCl) were studied in the 900–4000 cm^–1 range. Spectra were recorded for theN-MP-HCl-1,1,2,2-tetrachloroethane (TCE) ternary system at a TCE N-MP ratio of 1 1. Depending on the ratio between the components, complexes of the compositionN-MP · HCl (C-1),N-MP · 2HCl (C-2), and 2N-MP · HCl (C-3) are formed in the system. Complex C-1 has a quasiionic structure, (CH₂)₃N(Me)CO...H...Cl, formed by a strong quasisymmetrical H-bond between the carbonyl O atom and the Cl atom. The addition of anN-MP molecule to complex C-1 yields complex C-3, in which the quasiionic character of the bond betweenN-MP and HCl is retained. When excess HCl is present, the quasiionic structure is destroyed, theN-MP molecule is protonated, and the Cl^– anion interacts with HCl to give an ion with a strong symmetrical H bond (Cl...H...Cl)^–. Complex C-2 is an ion pair.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1757–1763, September, 1995.This work was carried out with financial support of the Russian Foundation for Basic Research (Project No. 93-03-18356).     

IR spectroscopic study of ion-molecular interactions in the methanesulfonic acid—N,N-dimethylformamide system

Complex formation in the methanesulfonic acid (MSA)-DMF system was studied by Multiple Attenuated Total Reflectance (MATR) IR spectroscopy at 30°C within the composition range from neat MSA up to neat DMF. Depending on the ratio of components, two types of complexes with a strong quasi-symmetrical H bond (1 and2) are formed. The uncharged complex1 is a quasi-ion pair with the (O…H…O) bridge. Complex2 is formed by a protonated DMF molecule and the (A…H…A)⁻ anion bound as an ion pair. It is established that complexes1 are solvated by DMF molecules in an excess of a base. Solvation or2 in an excess of an acid corresponds to a change from contact to contact-separated ion pairs. Continuous absorption spectra of charged and uncharged complexes1 and2 were obtained. The schemes of acid-base interactions in the MSA-DMF and HCl-DMF systems were compared. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2484–2489, December, 1998.     

Intermolecular interactions in orthophosphoric acid-<Emphasis Type="Italic">N,N</Emphasis>-dimethylformamide system according to viscometric data

The viscosity of an orthophosphoric acid—N,N-dimethylformamide system was measured in the whole region of compositions at 298–338 K. An excess viscosity of the system was analyzed by the data obtained using different model concepts. Calculations suggested that strong intermolecular interactions and the formation of complexes (H₃PO₄)₂·DMF occur in the system. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2252–2256, October, 2005.     

Intermolecular interactions of (5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetrabutylporphyrinato)manganese acetate with small organic molecules

The coordination properties of (5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetrabutylporphyrinato)-manganese(III) acetate toward small organic molecules in an inert solvent medium were studied. The values of the equilibrium constants of the process and the composition of the molecular complex were determined. The influence of the electronic and conformational factors of macrocycle on the value of the equilibrium constant was found. The geometry of isolated molecules of manganese porphyrinate and its molecular complexes was optimized by the quantum-chemical PM3 method. The structure of the reaction products favorable by the energy was theoretically found. A good agreement between the calculated and experimental data was obtained.     

Molecular interactions in a surfactant-water-polyacrylamide system, according to densimetry, viscometry, conductometry, and spectroscopy data

Molecular interactions in a surfactant-polyacrylamide-water system are investigated. It is established that the interactions affect such physicochemical parameters of the system as viscosity, density, surface tension, conductivity, and critical micelle concentration. It is shown that in a polyacrylamide-water system, raising the polyacrylamide concentration to 0.02% causes conformational changes in its macromolecule.     

IR Spectra, Polymorphism, and Intermolecular Interactions in Carboxylic Acids

This paper summarizes the results of our studies on the structural aspects of polymorphism and mesomorphous states in long-chain aliphatic compounds represented by the homologous series of alkyl-, alkoxybenzoic, and alkylcyclohexanecarboxylic acids and their completely or partially fluorinated analogs. The studies were carried out by vibrational IR spectroscopy (experiment, theory), calorimetry, polarization microscopy, and X-ray diffractometry. Conformational polymorphs have been found for the compounds, which differ in the bending of alkyl and fluoroalkyl radicals and in rotation of carboxyl groups and phenyl rings during phase transitions. Structural rearrangements and dynamic changes take place inside the nuclei of H-complexes. The dimers are partially dissociated, and open associates, chain associates, and monomers differing in their conformational composition are formed.     

Intermolecular noncovalent interactions with carbon in solution

One of the most familiar carbon-centered noncovalent interactions (NCIs) involving an antibonding π*-orbital situated at the Bürgi–Dunitz angle from the electron donor, mostly lone pairs of electrons, is known as n → π* interactions, and if it involves a σ* orbital in a linear fashion, then it is known as the carbon bond. These NCIs can be intra- or inter-molecular and are usually weak in strength but have a paramount effect on the structure and function of small-molecular crystals and proteins. Surprisingly, the experimental evidence of such interactions in the solution phase is scarce. It is even difficult to determine the interaction energy in the solution. Using NMR spectroscopy aided with molecular dynamics (MD) simulation and high-level quantum mechanical calculations, herein we provide the experimental evidence of intermolecular carbon-centered NCIs in solution. The challenge was to find appropriate heterodimers that could sustain room temperature thermal energy and collisions from the solvent molecules. However, after several trial model compounds, the pyridine-N-oxide:dimethyltetracyanocyclopropane (PNO–DMTCCP) complex was found to be a good candidate for the investigation. NBO analyses show that the PNO:DMTCCP complex is stabilized mainly by intermolecular n → π* interaction when a weaker carbon bond gives extra stability to the complex. From the NMR study, it is observed that the NCIs between DMTCCP and PNO are enthalpy driven with an enthalpy change of −28.12 kJ mol⁻¹ and dimerization energy of ∼−38 kJ mol⁻¹ is comparable to the binding energies of a conventional hydrogen-bonded dimer. This study opens up a new strategy to investigate weak intermolecular interactions such as n → π* interaction and carbon bonds in the solution phase.

NMR spectroscopy combined with MD simulation and electronic structure calculations enabled us to quantify the energetics of the intermolecular n → π* interaction and carbon-bonding (n → σ* interaction) in solution.     

Hydrate shell models of acetate ions according to nuclear magnetic relaxation data and quantum-chemical calculations

Different ion-water clusters for the CH₃COO^? ion that simulate the structure of its hydrate shells in solution are considered on the basis of the quantum mechanical approach. The possible coordination of water molecules around the ion is studied and the calculation results are compared with the experimental data obtained by nuclear magnetic relaxation.