Методами ИК спектроскопии и теории функционала плотности (B3LYP/6-31++G(d,p)) изучена конкуренция между молекулами метанола и воды при образовании ионов с сильными квазисимметричными Н-связями (CH3(Н)О⋯Н⋯О(Н)СН3)+, (CH3(Н)О⋯Н⋯ОН2)+, (Н2О⋯Н⋯ОН2)+ и их сольватации в системе СН3ОН—Н2О—HCl. Установлено, что при добавлении воды к раствору HCl в метаноле молекулы Н2О замещают молекулы СН3ОН в составе ионов (CH3(Н)О⋯Н⋯О(Н)СН3)+ с образованием смешанных дисольватов. Напротив, при добавлении метанола к водному раствору HCl ионы (Н2О⋯Н⋯ОН2)+ сохраняются, а молекулы СН3ОН участвуют в их сольватации. При соизмеримых долях метанола и воды в растворах одновременно присутствуют ионы (CH3(Н)О⋯Н⋯ОН2)+ и (Н2О⋯Н⋯ОН2)+. Соотношение их концентраций зависит от содержания HCl в системе. Показано, что основным фактором, определяющим структуру растворов CH3OH—H2O—HCl, в частности состав присутствующих в них дисольватов протона, является энергия существующей в этих растворах системы водородных связей, приходящихся на одну диссоциированную молекулу HCl.

IR spectroscopy and density functional theory (B3LYP/6-31++G(d, p)) are used to study the competition between methanol and water molecules during the formation of (CH3(H)O∙∙∙H∙∙∙O(H)CH3)+, (CH3(H)O∙∙∙H∙∙∙OH2)+, and (H2O∙∙∙H∙∙∙OH2)+ ions with strong quasi-symmetrical H-bonds and their solvation in the CH3OH–H2O–HCl system. When water is added to a solution of HCl in methanol, H2O molecules substitute CH3OH molecules in (CH3(H)O∙∙∙H∙∙∙O(H)CH3)+ ions to form mixed disolvates. Conversely, when methanol is added to an aqueous solution of HCl, (H2O∙∙∙H∙∙∙OH2)+ ions are maintained and CH3OH molecules are involved in their solvation. Provided that the fractions of methanol and water are commensurate, the solutions contain simultaneously (CH3(H)O∙∙∙H∙∙∙OH2)+ and (H2O∙∙∙H∙∙∙OH2)+ ions. The ratio between their concentrations depends on the content of HCl in the system. It is shown that the energy of the hydrogen bond system per one dissociated HCl molecule is the main factor determining the structure of CH3OH–H2O–HCl solutions, in particular, the composition of proton disolvates.

Методами ИК спектроскопии и квантовой химии исследованы особенности гидратации и определены концентрационно-структурные зоны в системе HCOOH—H2O. Из совместного анализа ИК спектров водных растворов HCOOH и результатов квантово-хими­ческого расчета комплексов (HCOOH)m⋅(H2O)n (m = 1—4, 6, n = 1—10, 14), HCO2–⋅(H2O)n (n = 2, 6) получены данные о составе и строении стабильных гетероассоциатов (ГА), образующихся в таких растворах. Установлена последовательность их образования при разбавлении 100%-ой кислоты водой. В диапазоне концентраций от 100 % НСООН до соотношения НСООН:Н2О = 1:1 вся вода входит в состав циклических ГА (НСООН)2⋅(Н2О)2 симметрии C2, являющихся самыми устойчивыми. Компоненты эквимолярного раствора практически полностью связаны в такие гидраты. При соотношениях НСООН:Н2О = 1:1—1:2 наряду с комплексами (НСООН)2⋅(Н2О)2 образуются менее стабильные (на ~10 %) циклические ГА НСООН⋅(Н2О)2. Раствор с двукратным избытком воды состоит из таких гидратов. При дальнейшем увеличении концентрации воды наблюдается последующая гидратация ГА НСООН⋅(Н2О)2.

Hydration in aqueous solutions of dimethylacetamide was studied by IR spectroscopy and quantum chemistry; the concentration and structural zones were determined. An analysis of the concentration dependences of IR absorption of these solutions at different frequencies showed that heteroassociates with stoichiometric ratios of components of 2 : 1, 1 : 1, 1 : 2, and 1 : 4 formed in them in sequence. The composition, structure, formation energy, and relative stability of the heteroassociates were determined from the results of DFT calculations for 19 hydrates. The stability of dimethylacetamide hydrates was shown to increase with the relative content of water molecules in them.

The composition and structure of complexes that formed in aqueous solutions of trifluoroacetic acid were studied by frustrated multiple total internal reflection IR spectroscopy (FMTIR). Two types of complexes with a molecular structure formed: trimers CF3COOH · (H2O)2 and cyclic tetramers (CF3COOH)2 · (H2O)2, in which the molecules of the components are arranged in pairs. In the range of acid concentrations from 100% to [H2O]/[CF3COOH] = 1: 1, only these tetramers formed, and all added water was bound into these hydrates. In more dilute solutions (up to [H2O]/[CF3COOH] = 2: 1), CF3COOH · (H2O)2 complexes formed along with tetramers; at a double excess of H2O, the components of the solution were completely bound into these trimers. In dilute solutions (from 0 to 3.6 M CF3COOH), the acid is completely dissociated into H5O 2 + and CF3COO– ions hydrated with water molecules. In the range of medium concentrations (from 3.6 M to [H2O]/[CF3COOH] = 2: 1), the solutions contain both these ions and CF3COOH · (H2O)2 dihydrates. For this range of compositions of the CF3COOH−H2O system, the concentrations of H5O 2 + ions and CF3COOH · (H2O)2 dihydrates were calculated.

Ion-molecular interactions in aqueous solutions of NaOH (0–47.8%) and KOH (0–51.95%) are studied by multiple frustrated total internal reflection IR spectroscopy. Interpretation of the spectra and analysis of the spectral data are performed based on the results of DFT calculations (B3LYP/6-31++G(d, p)) of the characteristics of the free and double hydrated H3O 2 - ion. It is established that the changes in the IR spectra of NaOH and KOH aqueous solutions caused by increasing alkali concentration are due to the formation of H3O 2 - ions with a strong quasi-symmetrical hydrogen bond and their subsequent hydration by one or two water molecules. The influence of the cation nature on the degree of hydration of H3O 2 - ions is demonstrated. The equilibrium concentrations of monohydrate (H3O 2 - ∙ H2O) and dihydrate (H3O 2 - ∙ 2H2O) are calculated and their IR continuous absorption spectra are isolated.

The method of frustrated multiple internal reflection (FMIR) infrared spectroscopy was used to study the nature of intermediates that formed upon oxidation of sulfur dioxide in trifluoroacetic acid (TFA) of various concentrations at 30°C. It was established that sulfur dioxide bound to a complex with TFA is oxidized by dissolved oxygen in systems that contain 99.9 and 55.5% trifluoroacetic acid.

The methanesulfonic acid (MSA)-diethylamine (DEA) binary liquid system is studied over the entire range of compositions at 30°C by using multiple frustrated total internal reflection IR spectroscopy. Solutions with acid: base equimolar ratio contain only 1 : 1 ion pairs. Upon adding the acid, a MSA molecule abstracts an anion from the 1 : 1 complex to produce a protonated DEA and an (H3C(O2)SO…H…OS(O2)CH3)− anion with a strong H bond: (C2H5)2(H)NH+ · OS(O2)CH 3 − + HOS(O2)CH3 ↔ (C2H5)2(H)NH+ + (H3C(O2)SO…H…OS(O2)CH3)−. This equilibrium is shifted to the left. The 1 : 1 complex is present in solutions even at an significant excess of the acid. To protonate the complex, it is required at least two MSA molecules. Under conditions of an excess of the base, DEA molecules do not solvate the 1 : 1 complex. The solution separates into two phases, composed of (C2H5)2(H)NH+ · OS(O2)CH 3 − complexes and pure DEA.

The methylsulfonic acid (MSA)—methanol (MeOH) liquid binary system was studied over the whole concentration range by the MBTIR IR spectroscopy method at 30°C. Quasi-ion pairs with the 1: 1 composition formed by a strong symmetrical H-bond were only present in solutions with an equimolar acid: base ratio. The addition of methanol caused the solvation of quasi-ion pairs by MeOH molecules, and, in the presence of the base in a substantial excess (C MeOH 0 : C MSA 0 > 2), proton disolvates (Me(H)O⋯H⋯O(H)Me)+ with strong symmetrical H-bonds were formed; that is, there was B⋯H⋯A + B ↔ (B⋯H⋯B)+ + A− equilibrium, where B is the base molecule and HA is the acid. In the presence of excess acid, methanol was protonated, and negatively charged proton disolvates were formed, B⋯H⋯A + HA ↔ BH+ + (AHA)−. This equilibrium was fully shifted to the right.

In concentrated solutions of methylsulfonic acid in butyl acetate (BA), molecular and ionic complexes were found to be in equilibrium: AH ⋯ B ⋯ HA + HA ↔ AH ⋯ BH^ + + (AHA)^ - . The base is fully protonated only at a more than 10-fold excess of the acid. In the presence of tetrachloroethane (TCE), a neutral solvent, the IR spectra of the system are indicative of an increase in the concentration of undissociated acid molecules (HA) and a decrease in the concentration of proton solvates (AHA) − . This means that the equilibrium shifts to the formation of molecular structures. At C TCE 0 : C BA 0 > 2, TCE molecules attenuate the promoting effect of undissociated acid molecules, which are known to facilitate the transfer of a proton to a base molecule with the formation of an (AHA) − ion with a strong symmetrical H-bond.

Ion–molecule interactions in the dichloroacetic acid–N,N-dimethylformamide system in the concentration range from pure acid to pure base at 30°C were investigated by multiple attenuated total internal reflectance IR spectroscopy. It was found that, depending on the ratio between components in solution, 1 : 1 or 2 : 1 acid–base complexes with strong hydrogen bonds are formed. With an excess of the acid, protonation of the base does not occur. The intensity of continuous absorption at 2000 cm–1 is characteristic of quasi-ionic pairs with strong symmetrical hydrogen bonds. However, along with a continuous component, the spectra exhibited individual sharp peaks, which are typical of molecular complexes.

The complex band of formaldehyde at 950-1150 cm(-1) in the IR spectrum of its aqueous solutions was resolved into individual bands by computer analysis. The calculated band intensities were compared with known concentrations of monomeric, dimeric, and trimeric formaldehyde species. The IR data are consistent with the published NMR data.

The method of multiple total internal reflection infrared spectroscopy (MTIRIRS) is used to study ion–molecular interactions in the system dichloroacetic acid–ethyl acetate in the range of concentrations from pure acid to pure base at 30°C. Depending on the ratio of components in the solution, molecular complexes with acid : base ratios of 1 : 1 or 2 : 1 are formed in the solutions. In the case of excess acid, base is not protonated and species with a strong symmetric hydrogen bond are not formed. It is shown that the absorption coefficient near 2000 cm –1 can be used to judge the type of the complex formed and the strength of a hydrogen bond in molecular complexes.

Complex formation in the trifluoroacetic acid (TFA)—DMF system containing TFA from 0 to 100 mol.% was studied by IR multiple attenuated total reflectance (MATR) spectroscopy at 30°C. The formation of uncharged 1∶1 TFA—DMF complexes with a quasi-ion structure and partial proton transfer to the O atom of the DMF molecule (quasi-ion pairs) were observed in the TFA—DMF system with the TFA content from 0 to 90 mol%. Depending on the ratio of the components, the quasi-ion pairs are solvated by the DMF or TFA molecules. The solvation of the quasi-ion pairs slightly changes the parameters of the central strong H bond. When the acid concentration reaches 80 mol.%, the proton adds to the DMF molecule to form the ion pair (DMF)H+·(A...H...A)−, whose anion contains a strong symmetric H bond.

The methanesulfonic acid (MSA)—propylene carbonate (PC) system with component concentrations of 0–100% was studied at 30°C using the Multiple Attenuated Total Reflection (MATR) IR spectroscopy. The formation of a strong 1∶1 molecular complex of MSA with PC was established. In the presence of an excess of the acid, a second MSA molecule adds to this complex to give the molecular complex (2MSA)·PC. When excess propylene carbonate is used, the MSA·PC complex is solvated by a propylene carbonate molecule. No protonation of the base or formation of complexes with a strong symmetrical H bond was observed. Continuous absorption was not detected in IR spectra of the solutions.

Ion-molecular interactions in the HCl−BuiOH system with different compositions (from neat isobutyl alcohol to 37 mol.% HCl) were studied by Multiple Attenuated Total Reflectance (MATR) IR spectroscopy at 30 °C. Proton disolvates (Bui(H)O…H…O(H)Bui)+ with strong symmetrical H bonds are formed upon the addition of HCl to BuiOH. At high concentrations of HCl (C 0 HCl>33 mol.%), (Cl…H…Cl)− ions are formed along with (BuiOH)2H+. The spectra of positively and negatively charged proton disolvates were compared to those of similar ions in the HCl−PriOH and HCl−MeOH systems.

The multiple attenuated total reflection IR spectra of solutions of sodium acetate in acetic acid have been recorded in the range from 9000 to 4000 cm−1. The CH3COO− anion and an acid molecule form be complex (CH3COO...H...OOCCH3) with a strong symmetric H-bond.