Solvent effects on infrared spectra of methyl 4-hydroxybenzoate in pure organic solvents and in ethanol/CCl4 binary solvents

Infrared spectroscopy studies of methyl 4-hydroxybenzoate (MHB) in 17 different organic solvents and in ethanol/CCl4 binary solvent were undertaken to investigate the solvent-solute interactions. The frequencies of carbonyl stretching vibration nu(C=O) of MHB in single solvents were correlated with the solvent acceptor number (AN) and the linear solvation energy relationships (LSER). The assignments of the two bands of nu(C=O) of MHB in alcohols and the single one of that in non-alcoholic solvents were discussed. The shifts of nu(C=O) of MHB in ethanol/CCl4 binary solvents showed that several kinds of solute-solvent hydrogen bonding interactions coexisted in the mixture solvents, with a change in the mole fraction of ethanol in the binary solvents.     

Solvent Effect on Characteristic Vibration of IR Spectrum of 4,4'-Dibromodiphenyl Ether

The optimal geometry, IR spectrum and vibration assignment of 4,4＇-dibromodiphenyl ether（BDE-15） in gas phase were calculated via the density functional theory（DFT） at the level of B3LYP/6-3 l＋G（d）. Based on the vi- bration assignment, the calculation of vibration frequencies and intensities of 5 main vibration types of BDE-15 in 25 kinds of solvents was carried out by means of a self-consistent reaction field（SCRF） theoretical model at the level of B3LYP/6-31＋G（d） to analyze the solvent effect on the vibration of IR spectrum of BDE-15. To study the solvent ef- fect further, C--O asymmetric stretching vibration fluctuating, which is relatively acute in both vibration frequency and intensity, was selected as the characteristic vibration to establish different linear solvation energy relation（LSER） models for solvent categoring. Solvent parameters（a, /3, ~r＊）, acceptable number（AN） and quantitative structure- activity relationship（QSAR） models were established via chemical quantum parameters of solvent moleculer, which were first been introduced to investigate different solvent-solute interaction mechanisms in alcoholic and non-alcoholic solvents on molecular level. At last, a single solvent molecule was embedded in the framework of po- larizable continuum model（PCM） to validate the effect of hydrogen bonding on solvent-solute interaction in alcohol solvents. The obtained results show that 5 main vibration types of BDE-15 in different solvents have small variation range in frequency and intensity and all the vibration frequencies in solvents are lower than those in gas phase, de- creasing along with the increasing of the dielectric Constant（e） of solvents exponentially. In contrast, all the vibration intensities in solvents are greater than those in gas phase and present positive exponential trend. Twenty-five solvents were divided into two categories（non-alcoholic solvents and alcoholic solvents） by LSER. The CmO asymmetric stretching vibration was mainly reg     

Ultrafast forward and backward electron transfer dynamics of coumarin 337 in hydrogen-bonded anilines as studied with femtosecond UV-pump/IR-probe spectroscopy

Femtosecond infrared spectroscopy is used to study both forward and backward electron transfer (ET) dynamics between coumarin 337 (C337) and the aromatic amine solvents aniline (AN), N-methylaniline (MAN), and N,N-dimethylaniline (DMAN), where all the aniline solvents can donate an electron but only AN and MAN can form hydrogen bonds with C337. The formation of a hydrogen bond with AN and MAN is confirmed with steady state FT-IR spectroscopy, where the C═O stretching vibration is a direct marker mode for hydrogen bond formation. Transient IR absorption measurements in all solvents show an absorption band at 2166 cm(-1), which has been attributed to the C≡N stretching vibration of the C337 radical anion formed after ET. Forward electron transfer dynamics is found to be biexponential with time constants τ(ET)(1) = 500 fs, τ(ET)(2) = 7 ps in all solvents. Despite the presence of hydrogen bonds of C337 with the solvents AN and MAN, no effect has been found on the forward electron transfer step. Because of the absence of an H/D isotope effect on the forward electron transfer reaction of C337 in AN, hydrogen bonds are understood to play a minor role in mediating electron transfer. In contrast, direct π-orbital overlap between C337 and the aromatic amine solvents causes ultrafast forward electron transfer dynamics. Backward electron transfer dynamics, in contrast, is dependent on the solvent used. Standard Marcus theory explains the observed backward electron transfer rates.     

Solvent-dependent resonance Raman spectra of high-valent oxomolybdenum(V) tris[3,5-bis(trifluoromethyl)phenyl]corrolate

UV-visible, infrared (IR), and resonance Raman (RR) spectra were measured and analyzed for a high-valent molybdenum(V)-oxo complex of 5,10,15-tris[3,5-bis(trifluoromethyl)phenyl]corrole (1) at room temperature. The strength of the metal-oxo bond in 1 was found to be strongly solvent-dependent. Solid-state IR and RR spectra of 1 exhibited the MoVO stretching vibration at nu(MoVO)=969 cm(-1). It shifted up by 6 cm(-1) to 975 cm(-1) in n-hexane and then gradually shifted to lower frequencies in more polar solvents, down to 960 cm(-1) in dimethyl sulfoxide. The results imply that stronger acceptor solvents weaken the MoVO bond. The 45-cm(-1) frequency downshifts displayed by 1 containing an 18O label in the molybdenum(V)-oxo unit confirmed the assignments for the observed IR and RR nu(MoVO) bands. The solvent-induced frequency shift for the nu(MoVO) RR band, measured in a series of 25 organic solvents ranging from n-hexane (AN=0.0) to N-methylformamide (AN=32.1), did not decrease in direct proportion to Gutmann's solvent acceptor numbers (ANs). However, a good linear correlation of the nu(MoVO) frequency was found against an empirical "solvent polarity" scale (A+B) of Swain et al. J. Am. Chem. Soc. 1983, 105, 502-513. A molecular association was observed between chloroform and oxomolybdenum(V) corrole 1 through MoO...H/CCl3 hydrogen-bonding interactions. This association manifested itself as a shift of the nu(MoVO) RR band of 1 in CDCl3 to a higher frequency compared to that in CHCl3.     

Modeling of tracer diffusion in liquids when solute–solvent interactions are present

The linear solvation energy relationship (LSER) model is employed to correlate the tracer diffusion coefficients of 550 binary systems at 298.15 K. Among the selected solutes and solvents there exist apolar, polar and hydrogen-bonding substances that can interact with themselves (solvent polymerization) or with the other compound (solute–solvent complexes formation). The results of the proposed formulas are compared with those of other predictive equations.     

Water in toluene revisited: vibrational patterns in the stretching region

The symmetric (v1) and antisymmetric (v3) stretching bands of water monomers in toluene are revisited using two approaches: (i) calculation of dipole autocorrelation functions (ii) the solvatochromic behaviour of both vibration frequency shifts. The time constants extracted from the autocorrelations account for meaningful differences between the couplings established by the antisymmetric and symmetric vibrations with the solvent. The dipole autocorrelation function for the symmetric stretching band fits well a Lorentzian spectral density and shows a higher contribution to hindered rotation relatively to the one obtained from the antisymmetric stretching. The spectral shifts of stretching frequencies in toluene and in other relevant solvents were interpreted as arising from the electronic and orientational polarisations. Characteristic donor/acceptor interactions also contribute to the red shift and were tested by using empirical solvent basicity scales such as Kamlet-Taft beta and the recently proposed SB. The deviations detected in toluene as regards the continuum dielectric predictions are quantitatively treated and account for the specific interaction between the water and the molecular pi electron system referred to in the literature.     

Solvent dependence of peak frequencies and bandwidths of the ν4 vibration of the series CH3MCl3, M  C,Si, Ge,Sn

The Raman spectra of the carbon—chlorine symmetric stretching mode, ν₄, of the Group IVA methylmetal trichlorides (CH₃MCl₃, M  C, Si, Ge, Sn) were acquired in a number of solvents of varying molecular properties. Non-linear curve fitting procedures were used to separate the four band components resulting from chlorine isotope splitting.The band maxima of the two lighter members of the series were observed to shift to lower frequency with increasing solvent polarizability, indicating the predominance of solute—solvent dispersion forces. In the germanium and tin compounds, on the other hand, the peak frequencies were correlated, instead, with solvent dipole moment. This result is in contrast to earlier studies on the ν₁ (CH₃ symmetric stretching) vibration, for which dispersion interactions are the dominant frequency displacement mechanism in all four compounds.The bandwidths of the ν₄ vibration were found to depend on dipolar interactions in the germanium and tin compounds. However, this correlation was not observed for the two lighter series members, nor for the carbon—chlorine antisymmetric stretching vibration in CH₃SnCl₃.     

Investigation of the solvation's processes of the ions in non-aqueous solutions by IR spectroscopy

IR spectra of solutions of LiCIO₄ (1), NaCIO₄ (2), LiI (3), NaI (4) in binary acetone — acetonitrile solvent were investigated in the region of CN (1–4), CC (1,3) and CH (3,4) stretching vibration bands of acetonitrile and CCC group (1) asymetric stretching vibration band of acetone at the wide range varying of the composition of the binary solvent. Infrared studies were also carried out on solutions of LiCIO₄ and NaCIO₄ in CH₃CNC₂H₅OH mixtures. The C N (1,2) and CC (1) stretching bands of acetonitrile were measured for 0.7–1.0M of CH₃CN. The observed intensities of IR bands allowed to calculate the solvating abilities of used solvents and to estimate the change of solvation sphere composition.     

Multi-wavelength spectrophotometric determination of the protolytic constants of tetracycline hydrochloride in some nonaqueous-water mixed solvents: a solvatochromism study

Annihilation of the contribution of one chemical component from the original data matrix is a general method in rank annihilation factor analysis (RAFA). However, RAFA is not applicable for studying the protonation equilibria of multiprotic acids but in this study two-rank annihilation factor analysis (TRAFA) was used as an efficient chemometrics algorithm for determination of the protolytic constants (pKa) of tetracycline hydrochloride (TCHC) in some nonaqueous-water mixed solvents such as acetonitrile (AN)-water and methanol (MeOH)-water from the spectral pH-absorbance data. The spectral data was obtained from spectrophotometric acid-base titrations of different solutions of TCHC at (25.0±0.10)°C and an ionic strength of 0.10 M. In TRAFA algorithm the pKa values were obtained with relationship between residual standard deviation (R.S.D.) and hypothetical pKa values. In the case of TCHC, the spectra were divided in two consecutive subdivisions according to their pH range having two pKa and TRAFA was run twice. The validity of the obtained pKa values was checked with well-known chemometrics algorithms such as DATAN, EQUSPEC, SPECFIT/32 and SQUAD. The effects of changing solvent composition on the protolytic constants were explained by linear solvation energy relationships (LSER) utilizing solvatochromic parameters.     

Solvent dependence of absorption intensities and wavenumbers of the fundamental and first overtone of NH stretching vibration of pyrrole studied by near-infrared/infrared spectroscopy and DFT calculations

Near-infrared (NIR) and IR spectra were measured for pyrrole in CCl(4), CHCl(3), and CH(2)Cl(2) to study solvent dependence of absorption intensities and wavenumbers of the fundamental and first overtone of NH stretching vibration. It was found that the wavenumbers of the NH fundamental and its first overtone decrease in the order of CCl(4), CHCl(3), and CH(2)Cl(2), which is the increasing order for of the dielectric constant of the solvents. Their absorption intensities increase in the same order, and the intensity increase is more significant for the fundamental than the overtone. These results for the solvent dependence of the wavenumbers and absorption intensities of NH stretching bands of pyrrole are quite different from those due to the formation of hydrogen bonds. Quantum chemical calculations of the wavenumbers and absorption intensities of NH stretching bands by using the 1D Schr?dinger equation based on the self-consistent reaction field (SCRF)/isodensity surface polarized continuum model (IPCM) suggest that the decreases in the wavenumbers of both the fundamental and the overtone of the NH stretching mode with the increase in the dielectric constant of the solvents arise from the anharmonicity of vibrational potential and their intensity increases come from the gradual increase in the slope of the dipole moment function.     

Solvent effects on OH stretching frequencies for 1-arylallyl alcohols

A series of 1-arylallyl alcohols were prepared and its OH stretching frequencies measured in 20 different non-HBD solvents at room temperature. It is noticed that the observed stretching bands were highly sensitive to the nature of the solvents. Multiple parameter equations were applied to investigate the solvent effects on the O-H stretching frequency. The most significant solvent parameters were the nucleophilicity measuring parameter (B) and Gutmann donor number (DN), whilst the electrophilicity measuring parameter (E) is not significant.     

Solvent effect on stretching vibration frequencies of the N-H and O-H groups of diphenylamine and phenol in complexes with various proton acceptors: Cooperative effect

Solvent effect on the stretching vibration frequencies of the O-H and N-H groups in complexes of phenol and diphenylamine with bases in aprotic and proton-donor solvents was studied by IR spectroscopy. Linear correlations of high quality were obtained between the frequencies of hydrogen-bonded O-H and N-H groups in these complexes in aprotic solvents and a new solvent parameter, S _VW. The cooperative effect of a proton-donor solvent on the strength of hydrogen bonds in complexes of phenol and diphenylamine with bases was evaluated. It was demonstrated for the first time that the cooperative effect in the examined systems can lead to both strengthening and weakening of hydrogen bonds.     

Raman spectroscopic study on solvation of diphenylcyclopropenone and phenol blue in room temperature ionic liquids

We investigated the solvation of several room temperature ionic liquids by Raman spectroscopy using diphenylcyclopropenone (DPCP) and phenol blue (PB) as probe molecules. We estimated acceptor numbers (AN) of room temperature ionic liquids by an empirical equation associated with the Raman band of DPCP assigned as a C=C stretching mode involving a significant C=O stretching character. According to the dependence of AN on cation and anion species, the Lewis acidity of ionic liquids is considered to come mainly from the cation charge. The frequencies and bandwidths of the C=O and C=N stretching modes of phenol blue are found to be close to those in conventional polar solvents such as methanol and dimethyl sulfoxide. The frequencies of these vibrational modes show similar dependence upon the electronic absorption band center as is observed in conventional liquid solvents. However, peculiar behavior was found in the Raman bandwidths and the excitation wavelength dependence of the C=N stretching mode in room temperature ionic liquids. Both the bandwidth of the C=N stretching mode and the extent of the excitation wavelength dependence of the Raman shift of the C=N stretching mode tend to decrease as the absorption band center decreases, in contrast to the case of conventional solvents. This anomaly is discussed in terms of the properties of room temperature ionic liquids.     

Solvent effect on SiH stretching bands of substituted silanes

Infrared frequencies of SiH stretching vibration bands of dimethyl naphthoxy silane and dimethyl quinoxy silane have been measured in a number of solvents. The results have been used to examine the importance of the bulk dielectric effect and specific solute—solvent interactions. The deviation from the Kirkwood—Bauer—Magat relationship produced by polar, as well as by non-polar, solvents is analysed in terms of the formation of molecular complexes.     

Hydrogen bonding effects on the wavenumbers and absorption intensities of the OH fundamental and the first, second, and third overtones of phenol and 2,6-dihalogenated phenols studied by visible/near-infrared/infrared spectroscopy

Visible, near-infrared (NIR) and IR spectra in the 15600-2500 cm(-1) region were measured for phenol and 2,6-difluorophenol, 2,6-dichlorophenol, and 2,6-dibromophenol in n-hexane, CCl(4), CHCl(3) and CH(2)Cl(2) to study hydrogen bonding effects and solvent dependences of wavenumbers and absorption intensities of the fundamental and the first, second, and third overtones of OH stretching vibrations. A band shift of the OH stretching vibrations from a gas state to a solution state (solvent shift) was plotted versus vibrational quantum number (v = 0, 1, 2 and 3), and it was found that there is a linear relation between the solvent shift and the vibrational quantum number. The slope of solvent shift decreases in the order of phenol, 2,6-difluorophenol and 2,6-dichlorophenol. For all of the solute molecules, the slope becomes larger with the increase in the dielectric constant of the solvents. The relative intensities of the OH stretching vibrations of phenol in CCl(4), CHCl(3), and CH(2)Cl(2) against the intensity of the corresponding OH vibration in n-hexane increase in the fundamental and the second overtone but decrease in the first and third overtones; the relative intensities show so-called "parity". The parity is more prominent for phenol that has an intermolecular hydrogen bonding than for 2,6-dihalogenated phenols that have an intramolecular hydrogen bond. These observations suggest that the intermolecular hydrogen bond between the OH group and the Cl atom plays a key role for the parity and that the intermolecular interaction between the solutes and the solvents (solvent effects) does not have a significant role in the parity.     

On the origin of ionic liquid‐induced variations in hydroxypropyl methacrylate propagation rate coefficients

Pulsed laser polymerizations were used to study the propagation kinetics of hydroxypropyl methacrylate (HPMA) in ionic liquids (ILs) and common organic solvents. The functional monomer was chosen to investigate the complex interplay of all interactions between monomer molecules and between monomer and solvent molecules and to obtain a deeper understanding of the impact of these interactions. The solvent effect on the HPMA propagation rate coefficient (k_p) was examined using a linear solvation energy relationship (LSER) based on Kamlet‐Taft solvatochromic parameters π*, α, and β. The results suggest that dipolarity/polarizability, associated with π*, and hydrogen bond–donating ability of the solvents, accounted for by α, majorly contribute to variations in k_p. Hydrogen bond–accepting (electron pair donating) ability of the solvents (β parameter) is of much lesser importance. In addition, LSER enables the prediction of HPMA k_p based on solvatochromic parameters of the solvents. The results suggest that interactions between the hydroxyl group of the monomer and the anion are dominant compared with classical hydrogen bonding between carbonyl and hydroxyl groups of the monomer units. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3188–3199, 2010     

Solvatation preferentielle dans les systemes ternaires polyvinylpyrrolidone/solvant halogene/solvant donneur de proton—II: Etude,par spectroscopie infra-rouge,des interactions hydrogene

We have studied, for dilute solutions of polyvinylpyrrolidone in halogenated solvent/protondonor solvent mixtures, the spectroscopic perturbations of the stretching vibration band v(CO) of the polymer and those of the stretching vibration band v(OH) in the particular case of trifluoroethanol. These measurements indicate a hydrogen-bond association polymer/proton-donor solvent, increasing with the proton-donor concentration in the mixture. The interaction with solvents such as trifluoroethanol and phenol is much stronger than that due to ethanol. Hydrogen-bond complexes are of $\text{1}\text{1}$ type. However, study of the v(CO) and v(OH) bands leads, in the case of trifluoroethanol, to the proposal of a complex of $\text{1}\text{2}$ type the structure of which is suggested.