Nonspecific Solvation Research Articles

Solvatochromic analysis and DFT computational study of N-(hexyl)-N-(5-(3-hydroxynaphthyl-2-yl)-1,3,4-oxadiazol-2-yl)amine

A detailed analysis of the molecular orbitals contained in the electronic transitions in the UV-spectra and a detailed synthesis and conformational study of N-(hexyl)-N-(5-(3-hydroxynaphthyl-2-yl)-1,3,4-oxadiazol-2-yl)amine (NOH) were conducted using the method of TD-DFT (B3LYP/6-311 + G (d,p)). All the theoretical results were found to be in line with the experimental values. For the most stable conformer, the optimized structure parameters (bond lengths, bond angles), vibrational modes and their assignments and were calculated using DFT/B3LYP functional and 6-311 +G(d,p) basis set. The basic vibrational modes were determined by PED, the experimental and computed values were found to support each other. The chemical shifts of 1H-NMR and 13C-NMR were specified using the method of GIAO and compared with the experimental chemical shifts. The frontier orbital energy gap, global chemical reactivity restrictive such as the chemical potential, global hardness, electronegativity, index of electrophilicity, global softness of the molecule were also studied. The Natural Bond Orbital (NBO) analysis was performed to find out the stability and strength of the molecule. Based upon the experimental solvent influence and the theoretical examinations, the long wavelength bands were attributed to π → π* transitions induced by HOMO–LUMO intra-molecular charge transfer from the naphthyl ring to the 1,3,4-oxadiazole. Beside these, electrophilic index, EHOMO (− 5.88 eV), ELUMO (1.89 eV) and energy gap (3.99 eV) were computed to investigate the bio activity, reactivity and stability of the NOH. Kamlet–Taft and Catalan solvatochromism of synthesized 1,3,4-oxadiazole derivative were discussed. The Kamlet–Taft and Catalan solvent parameter sets were used to determine the effect of specific and non-specific solvent–solute interactions on the shifts of UV–Vis absorption maxima.

Disentangling Time Scales of Vibrational Cooling, Solvation, and Hydrogen Bond Reorganization Dynamics Using Ultrafast Transient Infrared Spectroscopy of Formylperylene.

Unraveling dynamics of solvation and hydrogen bond (H-bond) reorganization between a solute and solvent is crucial to understand the importance of specific and nonspecific interactions in a solution-phase chemical reaction. Ultrafast time-resolved infrared (TRIR) spectroscopy provides direct opportunity to monitor site-specific intermolecular dynamics on a real-time scale by probing vibrational marker bands in the excited state of a solute. Herein, we report the real-time dynamics of vibrational cooling, solvation, and hydrogen bond reorganization of formylperylene (FPe) through TRIR spectroscopy of carbonyl (C═O) stretching mode in nonpolar, polar aprotic, and polar protic solvents. High sensitivity of the C═O stretch frequency (υ̅C═O) to photoinduced intramolecular charge transfer processes induced by specific and nonspecific solvent interactions led us to monitor the dynamics of dipolar solvation, site-specific H-bond formation, and reorganization processes by the TRIR method. In nonpolar cyclohexane, the υ̅C═O stretch band appears at 1610 cm-1 and exhibits negligible spectral shift over several tens of picoseconds. In acetonitrile, the υ̅C═O peak shifts to 1594 cm-1 and exhibits a further temporal red shift of about 5 cm-1 with a characteristic solvation time scale of acetonitrile (τ ∼ 0.5 ps). In methanol, υ̅C═O exhibits two bands corresponding to free and H-bonded FPe in early time scale. The free FPe population converts to the hydrogen-bonded population with a lifetime of about 10 ps. Vibrational cooling (τvc ∼ 12-20 ps) in the excited electronic state of FPe could independently be monitored from the temporal dynamics of the ring vibration mode, which is less sensitive to solvation and hydrogen bonding. The present study provides insight into the specific and nonspecific solvation-controlled charge transfer dynamics in aprotic and protic solvents using FPe as a probe.

Кинетика и механизм реакций ацильного переноса. Часть 15. Квантово-химическое моделирование механизмов реакций сульфонилирования N-этиланилина

The RHF/6-31G(d) quantum chemical simulation of the mechanism of the interaction of the secondary fatty aromatic amine N-ethylaniline with benzenesulfonyl chloride under conditions of non-specific water solvation, using the continuum model of the solvent, as well as of sulfonylation reactions of N-ethylaniline solvation complexes containing one water molecule, modeled specific solvation of N-ethylaniline with water, and one molecule of water and one of dioxane, which simulate the solvation of the amine with aqueous dioxane. Three-dimensional potential energy surface of these processes is calculated. It is shown that in the case of a reaction proceeding under conditions of non-specific solvation of reagents, the route with axial attack of the N-ethylaniline molecule to the sulfonyl reaction center is realized, in the two other cases the reactions proceed along a single route, starting as an axial attack of the nucleophile, which goes further with decreasing of the attack angle as reagent molecules approach each other. It was established that all the simulated reactions proceed in accordance with bimolecular coordinated mechanism of nucleophilic substitution SN2, which implies the formation of a single transition state in the reaction path. It was found that geometrical configuration of the reaction center in the transition state of N-ethylaniline reaction with benzenesulfonyl chloride under non-specific solvation by water is close to trigonal-bipyramidal, which is determined by the axial direction of the nucleophilic attack, in the two other cases it is medium between the trigonal-bipyramidal and tetragonal-pyramidal, which is associated with the change in the angle of N-ethylaniline attack as the reactant molecules approach each other. In a reaction involving N-ethylaniline monohydrate, a water molecule forms a 6-membered cyclic structure with reagent molecules in the transition state, in which the transfer of a proton from N-ethylaniline amino group to a hydrogen chloride molecule occurs via a relay mechanism involving the water molecule. The activation energy values of the studied processes were calculated; it is shown that both specific and universal solvation significantly lower the energy barrier of the reaction compared to the reaction occurring in gas phase, which is consistent with the data obtained earlier for related processes.

Effect of Solvents on Acid-Catalyzed Claisen Amino Rearrangement in N-(1-Methyl-2-butenyl)aniline

The effect solvents have on the processes of rearrangement and elimination in N-(1-methyl-2-butenyl)aniline (I) in the presence of HCl is studied. It is shown that the dependence of the rearrangement and elimination rate constants of (I) · HCl on the nature of solvents are described perfectly by the Koppel–Palm equation, which considers both nonspecific and specific solvation. The inhibitory effect of solvent nucleophilicity is explained by the complexation between (I) · HCl and solvent molecules. Analysis of the (I) · HCl conversion products obtained in a mixed solvent (m-toluidine + nitrobenzene) demonstrates the intermolecular transfer of the allyl moiety, confirming the formation of allyl cations in the Claisen amino rearrangement.

A Comparison of QM/MM Simulations with and without the Drude Oscillator Model Based on Hydration Free Energies of Simple Solutes.

Maintaining a proper balance between specific intermolecular interactions and non-specific solvent interactions is of critical importance in molecular simulations, especially when predicting binding affinities or reaction rates in the condensed phase. The most rigorous metric for characterizing solvent affinity are solvation free energies, which correspond to a transfer from the gas phase into solution. Due to the drastic change of the electrostatic environment during this process, it is also a stringent test of polarization response in the model. Here, we employ both the CHARMM fixed charge and polarizable force fields to predict hydration free energies of twelve simple solutes. The resulting classical ensembles are then reweighted to obtain QM/MM hydration free energies using a variety of QM methods, including MP2, Hartree–Fock, density functional methods (BLYP, B3LYP, M06-2X) and semi-empirical methods (OM2 and AM1 ). Our simulations test the compatibility of quantum-mechanical methods with molecular-mechanical water models and solute Lennard–Jones parameters. In all cases, the resulting QM/MM hydration free energies were inferior to purely classical results, with the QM/MM Drude force field predictions being only marginally better than the QM/MM fixed charge results. In addition, the QM/MM results for different quantum methods are highly divergent, with almost inverted trends for polarizable and fixed charge water models. While this does not necessarily imply deficiencies in the QM models themselves, it underscores the need to develop consistent and balanced QM/MM interactions. Both the QM and the MM component of a QM/MM simulation have to match, in order to avoid artifacts due to biased solute–solvent interactions. Finally, we discuss strategies to improve the convergence and efficiency of multi-scale free energy simulations by automatically adapting the molecular-mechanics force field to the target quantum method.

The hydrogen bonding enthalpies of water and methanol in ionic liquids

The thermochemical study of hydrogen bonding of water with different proton acceptor ionic liquids was carried out. Along with the available experimental data, the solution enthalpies of water in [BMIM][TfO], [BMIM][BF4] and [BMIM][PF6] were measured. The hydrogen bonding enthalpies of water with various ionic liquids were determined by using previously developed method of solvation enthalpy separation into the nonspecific solvation enthalpy and the specific solute-solvent interaction enthalpy (hydrogen bonding). The findings indicate the formation of a complex, where one molecule of water is bound to two molecules of ionic liquids. Similarly, hydrogen bonding enthalpies of methanol with the same proton acceptor ionic liquids were determined.

Solvent, structural, quantum chemical study and antioxidative activity of symmetrical 1-methyl-2,6-bis[2-(substituted phenyl)ethenyl]pyridinium iodides

15 symmetric 1-methyl-2,6-bis[2-(substituted phenyl)ethenyl]pyridinium iodides were synthesized in this work. Their structures were characterized using IR, 1H and 13C NMR, and UV–Vis spectroscopy. DFT calculations indicated that s-trans/s-trans conformation prevail in all compounds. The effects of specific and non-specific solvent–solute interactions on the UV–Vis absorption maxima shifts were evaluated using linear solvation-free energy relationships (LSER), i.e., Kamlet–Taft and Catalan models. A linear free energy relationship (LFER) in the form of single substituent parameter equations (SSP) was used to postulate quantitative structure–property relations of substituent effect on NMR data. TD-DFT results showed dependence of electronic transition on the substituent effects. The push–pull character of these compounds was analyzed by differences in 13C chemical shift of the ethylenic double bond in 2- and 6-positions of cross-conjugated with pyridinum central ring. Also, the quotient of the occupations for the bonding π and anti-bonding π* orbitals of this bond was considered. Good correlations of the selected parameter between double bond lengths with π*/π and 13C chemical shift differences of the bridging group proved them to be adequate descriptor of push–pull character. Synthesized compounds were screened for the antioxidant activity, using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical methods, and results demonstrated moderate antioxidant potential.

The Role of Solvation in the Kinetics and the Mechanism of Hydroperoxide Radicals Addition to π‐Bonds of 1,2‐Diphenylethylene and 1,4‐Diphenylbutadiene‐1,3

ABSTRACTA combination of microcalorimetry, the rotating sector method, and ESR at 323 K in the environment of 10 solvents of different polarities was used to measure rate constants of addition of hydroperoxide radicals () to π bonds of trans‐1,2‐diphenylethylene and trans,trans‐1,4‐diphenylbutadiene‐1,3 (k2) and disproportionation rate constants of these radicals (k3). With increasing dielectric constant of the medium, k2 values increase from 69 to 410 M−1 · s−1, and k3 values almost do not change and are in the range of (1.0 ± 0.2) × 108 M−1 · s−1. A linear dependence of logarithm values of rate constants from the dielectric constant of the medium in the coordinates of the Kirkwood–Onsager equation was found that allows to make a conclusion about the effect of nonspecific solvation in the studied systems. The quantum‐chemical analysis (NWChem, DFT B3LYP/6‐311G**) of the detailed mechanism for addition shows that the influence of the medium polarity reflects the superposition of the effects of nonspecific and specific solvation. The scale of the polar effect will depend on how different solvation energies of the transition and the initial reaction complexes. If a value of the solvation energy of the transition complex is larger than the solvation energy of the initial reaction complex, then the reaction rate should increase with an increase of the solvent's polarity and decrease otherwise.

The effect of solvation on the reactivity of 1,1-substituted ethylenes in hydroperoxyl radical addition reactions

The effect of solvation on the rate constants of hydroperoxyl radical addition to the double bonds of 1,1-substituted ethylene vinyl compounds was studied in the medium of different polarity solvents. The values of rate constants of this process were determined in a series of experiments on the co-oxidation of diphenylethylene (was used as the source of hydroperoxyl radicals) with the studied vinyl compounds at 323 K using the method of microvolumetry in combination with ESR spectroscopy and computer kinetic modeling. The observed linear relationship between the values of rate constant logarithms and the dielectric permittivity of reaction medium in coordinates of the Kirkwood–Onsager equation allows for the conclusion that the effect of nonspecific solvation due to the electrostatic forces does take place in the studied systems.

Theoretical Models for Quantitative Description of the Acid-Base Equilibria of the 5,6-Substituted Uracils.

The acidities of 18 5,6-substituted uracils have been numerically estimated as pKa values in terms of three theoretical models. The first scheme includes the calculation of the gas-phase acidity of uracil with the G3MP2B3 method and taking into account the solvent effect using the polarizable continuum approximation PCM(SMD)-TPSS/aug-cc-pVTZ. The second model is one step and implies calculation of the free Gibbs energies of the hydrate complex of uracil (and its anion) with 5 water molecules by the TPSS/aug-cc-pVTZ method. This model accounts for the solvent effect corresponding to both specific and nonspecific solvation. The third scheme required high time and computational resources and includes the strong features of the two previous schemes. Here, the theoretical estimation of pKa is performed by the CBS-QB3 composite method. As in the second approach, both specific (as pentahydrate) and nonspecific solvent effects are determined. We have analyzed the advantages and model restrictions of the considered schemes for the pKa calculations. All models have systematic errors, which have been corrected with the linear empirical regression relations. In the presented model, the absolute mean deviations of the pKa values of uracils dissociating via the N1-H bonds diminish to 0.25, 0.28, and 0.23 pKa units (respectively, for I, II, and III models), which corresponds to ∼0.3 kcal/mol on the energy scale. The applicability of our computational schemes to uracils dissociating via N3-H, O-H (orotic acids) and C-H bonds is discussed.

Controlled stabilization of anionic forms of the uracil derivatives: A DFT study

Relative stabilities of the N1/N3/О5/О6 anions of 42 substituted uracils in gas phase and aqueous solutions have been theoretically studied using approximation IEFPCM (SMD) − TPSS/aug-cc-pVTZ. The specific solvation of uracil and its anions has been simulated with the first hydrate shell made up with 5 water molecules. The nonspecific solvation has been accounted in terms of the SMD model. We have found a series of relative stability under conditions of both specific and nonspecific hydration. The series is ranked according to the increase of the relative stability of the N3 anion. In gas phase, the N1 anion is significantly more stable than its N3 counterpart: the ΔGgas values vary in the range from 19.54 (5OH6СН3U) to 83.14 (5NO26NH2U) kJ/mol that is caused by a more effective delocalization of the excess charge through the uracil framework in the N1 anion. The hydration pronouncedly diminishes ΔG to the range from ‐0.02 (5OH6СН3U) to 38.16 (5Br6NO2U) kJ/mol due to the fact that the polar solvent is prone to stabilize more polar anionic states of uracils. Therefore, less polar uracil anions are more stable. We have defined the main factor influencing the N1/N3/О5/О6 distribution of anions, viz. the presence of the substituents in 5 and 6 positions of the pyrimidine ring. Herewith, the most favorable mechanism of the influence of 5-substituents has been previously defined as resonant whereas, as we found in this work, the inductive mechanism is more pronounced in the case of 6-substituents.

Metal-catalyzed rearrangement of allenylsulfides to furan: A theoretical mechanistic approach

A furan catalytic synthesis from allene is studied with quantum chemistry computations. Both specific and non-specific solvent effect are considered. The complete catalytic cycle is studied for three metals, and compared to experimental data. The mechanism is disclosed and the catalyst regeneration shows clear difference between the three metals. For Pt, the regeneration corresponds to a two-steps mechanism with a stable intermediate. For Au and Ru catalysts the regeneration is a one step mechanism with a low barrier only for Au (3.8kcal/mol). For Au, the results of the computations contrasts with the experiments, hence a poisoning of the catalyst is most likely. On the contrary, in the Ru case, the regeneration corresponds to the highest transition state of the cycle.

Dispersive Optical Activity of (R)-Methylene Norbornene: Intrinsic Response and Solvation Effects.

The dispersive optical activity of a homoconjugated bicyclic diene, (R)-methylene norbornene (R-MNB), was interrogated under complementary vapor-phase and solution-phase conditions to elucidate the structural/electronic provenance of its unusual chiroptical signatures and to explore the marked influence of environmental perturbations. The intrinsic (isolated-molecule) values of specific rotation measured at 355 and 633 nm (1623.5 ± 5.5 and 390.4 ± 3.7 deg dm-1 (g/mL)-1) were found to be factors of 3.9 and 2.1 smaller in magnitude than analogous quantities obtained for the kindred enone, (R)-norbornenone (R-NBO), reflecting, in part, the loss of prominent magnetic-dipole contributions from the C═O moiety and the exclusion of electron delocalization from the oxygen lone pairs. The wavelength-resolved rotatory powers of R-MNB were enhanced dramatically (by ∼40% on average) upon dissolution in any of the four common solvents targeted by the present study (acetonitrile, di-n-butylether, cyclohexane, and chloroform), yet displayed only a slight dependence on the exact nature of the surrounding liquid (±2.7% variation from the mean at 589.3 nm). Quantum-chemical calculations built upon the linear-response frameworks of density-functional theory and coupled-cluster theory were enlisted to interpret experimental results, with the substantial effects incurred by nonspecific solvation phenomena being explored through use of polarizable continuum models and bulk property-response relationships. Aside from enumerating the varied quality of agreement attained between computational predictions and polarimetric measurements, these efforts have found that refractive-index correlations, akin to those embodied in the venerable (albeit often discounted) Lorentz local-field correction, afford a viable means of linking the chiroptical behavior of R-MNB across phases.

A detailed experimental and computational study of monocarbohydrazones

The substituent and solvent effect on intramolecular charge transfer (ICT) of twelve monocarbohydrazones (mCHs) were studied using experimental and theoretical methodology. The effects of specific and non-specific solvent–solute interactions on the UV–Vis absorption maxima shifts were evaluated using linear free energy relationships (LFERs) principles, i.e. using the Kamlet-Taft and Catalán models. Linear free energy relationships in the form of single substituent parameter equation (SSP) was used to analyze substituent effect on UV–Vis, NMR and pKa change. According to crystallographic data and quantum chemical calculations, the trans (E) form was found to be more stable. A photochromism of compounds with 2-hydroxyphenyl and 2-pyridylimino groups substituted at imine carbon atom results in E/Z isomerization due to creation of intermolecular hydrogen bond in E and Z form, respectively. Multiple stage mass spectrometry (MS-MSn) analysis was applied to define main fragmentation pathways. Furthermore, the experimental findings were interpreted with the aid of ab initio MP2/6–311G(d,p) and time-dependent density functional (TD-DFT) methods. TD-DFT calculations were performed to quantify the efficiency of intramolecular charge transfer (ICT) with the aid of the charge-transfer distance (DCT) and the amount of transferred charge (QCT) calculation. It was found that both substituents and solvents influence electron density shift i.e. extent of conjugation, and affect ICT character in the course of excitation.

Enhanced antitumor effect of poly(L-glutamic acid)-rose bengal conjugate nanoparticle

The photophysical properties of two N-salicylidene p-X-anilines (XCN, COOH) were studied in a series of solvents with varying polarity and proticity by steady state absorption and emission spectroscopy. The two compounds are dually fluorescent in solution due to an excited state proton transfer. The solvatochromic shifts were used to connect the solvent polarity parameter to the dipole moment in excited state using several approaches. The multiparameter Kamlet–Taft and Catalán solvent scales with four parameters have been employed to analyze the specific and non-specific solvent–solute interactions. The absorption spectra are less sensitive to the substitution at the aniline ring and to the solvent properties than the fluorescence spectra. Especially the ratio between the normal and abnormal Stokes shifted fluorescence intensities is dependent on the polarity and hydrogen bonding abilities of the solvent. The increasing solvent viscosity led to a decrease in the ratio of the intensities of the two emissions.

Liquid water changes its structure at 43 °C

Analysis of the changes in specific (HBD acidity and HBA basicity) and general nonspecific (polarizability and dipolarity) solvent interactions in liquid water, as determined by means of solvatochromic probes, shows that this liquid undergoes an internal structural change with increasing temperature, connected with a small increase of its polarizability and basicity as well as a comparatively larger decrease of its dipolarity. This change in the structure of water shows up in a non-uniform change in the behavior of these solvent parameters in going to temperatures higher than 43°C. Liquid water simultaneously decreases its acidity with the rise of temperature.

Solvent and substituent effect on intramolecular charge transfer in 5-arylidene-3-substituted-2,4-thiazolidinediones: Experimental and theoretical study

The substituent and solvent effect on intramolecular charge transfer (ICT) in 5-arylidene-3-methyl-2,4-thiazolidinediones (series 1) and 5-arylidene-3-phenyl-2,4-thiazolidinediones (series 2) was studied by using experimental and theoretical methodology. The effect of specific and non-specific solvent–solute interactions on the UV–vis absorption maxima shifts was evaluated by using the Kamlet-Taft and Catalán solvent parameter sets. Linear free energy relationships (LFERs) have been applied to the UV–vis and 13C NMR data by using SSP (single substituent parameter) and DSP (dual substituent parameters). Comparative LFER analysis of 10 styrenic series was performed in order to distinguish contribution of structural and electronic substituent effect on extent of π-polarization in a side chain (vinyl) group. Furthermore, the experimental findings were interpreted with the aid of ab initio MP2 and time-dependent density functional (TD-DFT) methods. TD-DFT calculations are performed to quantify the efficiency of intramolecular charge transfer (ICT) allowing us to define the charge-transfer distance (DCT), amount of transferred charge (QCT), and difference of dipole moments between the ground and excited states (μCT). It was found that both substituents and solvents influence electron density shift, i.e. extent of conjugation, and affect intramolecular charge transfer character in the course of excitation.

Solvatochromic properties of two related N-salicylidenanilines with dual fluorescence

The photophysical properties of two N-salicylidene p-X-anilines (XCN, COOH) were studied in a series of solvents with varying polarity and proticity by steady state absorption and emission spectroscopy. The two compounds are dually fluorescent in solution due to an excited state proton transfer. The solvatochromic shifts were used to connect the solvent polarity parameter to the dipole moment in excited state using several approaches. The multiparameter Kamlet–Taft and Catalán solvent scales with four parameters have been employed to analyze the specific and non-specific solvent–solute interactions. The absorption spectra are less sensitive to the substitution at the aniline ring and to the solvent properties than the fluorescence spectra. Especially the ratio between the normal and abnormal Stokes shifted fluorescence intensities is dependent on the polarity and hydrogen bonding abilities of the solvent. The increasing solvent viscosity led to a decrease in the ratio of the intensities of the two emissions.

The interplay of proton accepting and hydride donor abilities in the mechanism of step-wise boron hydrides alcoholysis

The reaction mechanism for the step-wise alcoholysis of BH4−, THF·BH3, Me2NH·BH3 and BH3 by ROH [ROH=CH3OH, CF3CH2OH (TFE) and (CF3)2CHOH (HFIP)] was studied computationally. The calculations were performed in gas phase at the DFT/M06/6-311++G(d,p) theory level taking into account non-specific solvent effects by SMD approach. The dihydrogen bonded complexes BH⋯HOR are the intermediates of this cascade borohydride alcoholysis, which set the proper orientation of the reactants molecules and direct their further activation. The consecutive introduction of RO groups instead of hydride ligands in [(RO)nBH(4−n)]− (n=0–3) decreases the dihydrogen bond strength due to the stabilization of borohydride HOMO orbital and the decrease of molecular electrostatic potential. Nevertheless the BH bond polarization and thermodynamic hydricity (hydride donor ability) increase with substitution, leading to the decrease of the reaction barrier. The HH bond formation can be considered as a result of concerted proton and hydride transfer in transition state. For BH4− alcoholysis the highest activation barrier was computed for the first reaction step: BH4−+HOR→H2+[(RO)BH3]− and the reaction is self-accelerating. The proton accepting and hydride donor abilities of neutral 4-coordinate borohydrides X·BH3 (X=THF, NHMe2) are lower than those of BH4−. Accordingly the activation barriers change in the order BH4−<THF·BH3<Me2NH·BH3 and at any reaction stage they remain higher than the barrier for the reaction of [(RO)BH3]− with the same alcohol. Together with low activation barrier for BX bond dissociation (X=O, N) this suggests the ligand exchange and the switch to the kinetically more favorable [(RO)BH3]− alcoholysis.

Calculation of Vibrational Spectra for Coordinated Thiocyanate Ion in Acetonitrile

The impact of the association of lithium cation with NCS– ion in acetonitrile on the vibrational spectrum was studied by the density-functional method in the B3LYP/6-31+G(d,p) approximation. The best agreement between experimental and calculated ionic association data was achieved taking into account the nonspecific solvation, oversolvation, and solubility of ionic complexes within the discrete-continuum model. The microstructures of the thiocyanate ion in a contact ion pair with lithium cation and ion-pair dimer and trimer in acetonitrile were established.