Acid–Base Interactions in the Dichloroacetic Acid–N,N-Dimethylformamide System as Found from IR Spectroscopic Data

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.     

Acid–Base Interactions in the Dichloroacetic Acid–Ethyl Acetate System according to IR Spectroscopic 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.     

Ions with a strong symmetric H-bond in solutions of sodium acetate in acetic acid

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.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp, 1854–1857, July, 1996.     

Proton solvation in methanol solutions of HCl

The MFTIR IR spectra of solutions of HCl in methanol were obtained in the 900–4000 cm^–1 frequency range. It was found that each proton binds two molecules of methanol. The spectra exhibit intense, continuous absorption (CA) with an intensity coefficient at 2000 cm^–1 of 174±10 liter/(mole·cm), which is in agreement with the corresponding coefficient for H₅O ₂ ⁺ . The optical densities of CA are linear functions of the concentration of HCl at 900–1600 cm^–1; there is no linearity at higher frequencies for C_HCl>4 M, and there are less than two molecules of MeOH for each (MeOH)₂H⁺ ion. The results obtained are in agreement with the model in which CA arises in solutions of strong acids because of the interaction of proton vibrations in a strong symmetric H bond with the vibrations of other groups of the proton disolvate.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2261–2268, October, 1992.     

Proton solvation in the sulfuric acid-water-1,4-dioxane system

The dependence of the optical density on the composition of the solution in the range of 0–60%, 1,4-dioxane in 10% aqueous solution of H₂SO₄ was obtained by FMIR IR spectroscopy. It was shown that in the solutions studied, the proton is in the form of the two simplest stable solvates: H₅O₂ ⁺ and H₂OHD⁺ ions, where D is the 1,4-dioxane molecule. The equilibrium concentrations of the proton solvates were estimated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 298–301, February, 1990.     

Ions with a strong symmetrical H bond in the HCl−BuiOH system by IR spectroscopy data

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. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2496–2500, December, 1998.     

GC determination of N-nitrosamines by supersonic molecular beam MS equipped with triple quadrupole analyzer, GC/SMB/QQQ/MS

The determination of 14 N-nitrosamines by a supersonic molecular beam electron ionization mass spectrometer equipped with triple quadruple analyzer, GC/SMB/EI/QQQ/MS is presented. The supersonic molecular beam electron ionization ion source allows the elucidation of the molecular ion of 13 out of the 14 examined nitrosamines (except for diphenylnitrosamine which was degraded before the analysis). It was possible to use the molecular ions of all the nitrosamines as the parent ions for multiple reactions monitoring mode, which in turn allows significant increase of specificity and lowering of the method limit of detection of the higher molecular weight nitrosamines. The instrumental LOD for different N-nitrosamines was 1–5 pg injection⁻¹. The proposed method was exemplified by analysis of N-nitrosamines and N-nitrosatables in rubber teats according to the British Standard BS EN 12868:1999.     

Complexes with strong symmetric hydrogen bonds and their solvation in the trifluoroacetic acid—N,N-dimethylformamide system studied by IR spectroscopy

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.     

Equilibrium Composition of Formaldehyde Oligomers in Aqueous Solutions from IR Data

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.