Solvent Acceptor Number Research Articles

Solvents effect on infrared spectra of trimethyl phosphate in organic solvents

Infrared spectroscopy studies of trimethyl phosphate (TMP) in 17 different pure organic solvents were undertaken to investigate the solvent–solute interactions and to correlate solvent properties such as the Kirkwood–Bauer–Magat (KBM) equation, the solvent acceptor number (AN) and the linear solvation energy relationships (LSER), respectively, with the infrared band shift. Poor correlation between dielectric constants and the frequencies showed that the KBM relationship was unsuitable for the investigated molecules. These frequencies exhibited a better correlation with the LSER than the solvent AN.

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 ν(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 ν(CO) of MHB in alcohols and the single one of that in non-alcoholic solvents were discussed. The shifts of ν(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 effects on infrared spectra of methyl 4-hydroxybenzoate in pure organic solvents and in ethanol/CCl 4 binary solvents

Infrared spectroscopy studies of methyl 4-hydroxybenzoate (MHB) in 17 different organic solvents and in ethanol/CCl 4 binary solvent were undertaken to investigate the solvent–solute interactions. The frequencies of carbonyl stretching vibration ν(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 ν(CO) of MHB in alcohols and the single one of that in non-alcoholic solvents were discussed. The shifts of ν(CO) of MHB in ethanol/CCl 4 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 Effects on Infrared Spectra of Methyl Methacrylate

Infrared spectroscopy studies of methyl methacrylate (MMA) in 20 different organic solvents were undertaken to investigate the solute–solvent interactions. The frequencies of carbonyl stretching vibration νC˭O of MMA were correlated with the solvent properties such as the KBM parameter, the solvent acceptor number (AN), and the linear solvation energy relationships (LSER). The solvent‐induced stretching vibration frequency shifts showed a better correlation with LSER than AN while the correlation with the KBM parameter was not good.

Solvent effects on infrared spectra of 2-acetylthiophene in organic solvents

Infrared spectroscopy studies of 2-acetylthiophene (ACTH) in 18 different organic solvents, both polar and non-polar, were undertaken to investigate the solvent–solute interactions. The frequencies of carbonyl stretching vibration υ(CO) of ACTH were correlated with the properties such as the solvent acceptor number (AN) and the linear solvation energy relationships (LSER). The solvent-induced stretching vibration frequency shifts showed a better correlation with the LSER than the AN. A six-membered ring-like hydrogen bonding structure was presented and the solvent effects of ACTH in alcohol solvents were investigated in detail.

Excited singlet state and photoionization of 8-methoxypsoralen. Picosecond transient absorption study.

Time-resolved pico- and nanosecond transient absorption measurements of 8-methoxypsoralen (8-MOP) were performed in different solvents at room temperature. The excited singlet state has two strong absorption bands with maxima at 430 and 630-690 nm. The lifetime of the first excited singlet state, tau(s), ranges from <10 ps up to 2.7 ns, being shorter in low-polar solvents (toluene, THF) and longer in highly polar water, TFE and HFIP. The rate of the singlet depopulation decreases exponentially with increasing solvent polarity as expressed by the Dimroth-Reichardt (ET(N)) or Gutmann solvent acceptor number (AN). In aqueous ethanol solution (H2O: EtOH 10:1), addition of the synthetic nucleobase 2-aminopurine slightly decreased the lifetime tau(s). The long-time (t > 5 ns) absorption spectrum remaining after the complete decay of the S1 state is due to the hydrated electron e(aq) and the radical cation 8-MOPF.+. Ionization is due to both, one and two-quantum excitation. In the intensity range I = 10(6)-10(9) W cm(-2) the quantum yield of electron ejection (ionization) phi(i) does not depend on the intensity of radiation, therefore the ionization is monophotonic, phi(i) = 0.03. At intensities 1> 5 x 10(9) W cm(-2) phi1 becomes larger due to two-quantum excitation followed by ionization.

Styrene Polymerization in Aprotic Solvents during the Electrogeneration of Radical Ketyl Anions

The voltammetry, ESR- and UV-spectroscopy methods and quantum chemical calculations (CNDO/2) are used to establish the nature of active centers and an anion mechanism of the polystyrene electrosynthesis during the reduction of 9-fluorenone (R) in a monomer–aprotic solvent–NaClO4 system. The higher the solvent's acceptor number, the lower the R·– generation potentials. The conversion of styrene increases with its donor number.

Solvent effects on infrared spectra of 5-methyl-7-methoxy-iso-flavone in single solvent systems

Infrared spectroscopy studies of 5-methyl-7-methoxy-iso-flavone in 20 different pure organic solvents were undertaken to investigate the solvent–solute interactions and to correlate solvent properties such as the Kirkwood–Bauer–Magat (KBM) equation, the solvent acceptor number (AN) and the linear solvation energy relationships (LSER), respectively, with the infrared band shift. Little linear relation between dielectric constants and the frequencies showed that the KBM relationship was unsuitable for the complicated molecules. These frequencies exhibited a better correlation with the LSER than the solvent AN.

An IR study on ion-specific and solvent-specific swelling of poly( N-vinyl-2-pyrrolidone) gel

Swelling degrees of poly( N-vinyl-2-pyrrolidone) (PVP) gel were measured in aqueous salt solutions and in water/organic solvent mixtures to find marked ion- and solvent-specificities. In order to investigate any correlation of those specificities with hydration or solvation of PVP, IR spectra band of the CO group was monitored by means of ATR method both for PVP gel and the relevant solution systems. Dependence of the peak frequency on the swelling ratio suggested that hydration of PVP carbonyl group in deswollen gel systems is different from that in the corresponding solution systems. In the solution systems, PVP carbonyl band showed a high-wavenumber shift for deswollen systems, which can be well correlated with changes in water proton charge through ionic hydration and with Gutmann's acceptor number of organic solvents. In the deswollen gel systems, the CO band showed a low-wavenumber shift, suggesting a strong hydration or doubly hydrated state. This unexpected behavior was interpreted by assuming an intermolecular hydrogen bond of two carbonyl groups intermediated by water molecules.

The synthesis and characterization of potassium 2,2'-bipyridinetetranitroruthenate.

We report a convenient synthesis of K(2)[Ru(bpy)(NO(2))(4)] via the thermal displacement of benzene from [(Bz)Ru(bpy)Cl]Cl (Bz = eta(6)-C(6)H(6); bpy = 2,2'-bipyridine) by nitrite ion in methanol solution. K(2)[Ru(bpy)(NO(2))(4)] has been fully characterized by elemental analysis, X-ray crystallography, and (1)H NMR, IR, UV-vis, and emission spectroscopy. Reaction of K(2)[Ru(bpy)(NO(2))(4)] with pyridine under mild or forcing conditions produces fac-K[Ru(bpy)(NO(2))(3)(py)] and cis-[Ru(NO(2))(2)(bpy)(py)(2)] (py = pyridine), respectively. We report full characterization data for these compounds, including crystal structures. The d pi(Ru) --> pi*(bpy) charge-transfer band in the electronic spectra of K(2)[Ru(bpy)(NO(2))(4)] and fac-[Ru(bpy)(NO(2))(3)(py)] displays a significant solvent dependence. The energy of the absorption band correlates linearly with the Gutmann solvent acceptor number. The solvatochromic response of these nitro complexes is essentially identical to that of the analogous cyanide complexes, indicating that the mechanism previously proposed to explain the solvatochromism of the cyanide complexes may need to be reexamined.

Solvent-dependent C-OH homolysis and heterolysis in electronically excited 9-fluorenol: the life and solvation time of the 9-fluorenyl cation in water.

The primary pathways of the photodecomposition of 9-fluorenol (FOH) were studied in polar and nonpolar solvents by use of laser flash-photolysis with a resolution time of 10 ps. In solvents of high polarity, that is, in 1,1.1,3,3,3-hexafluoroisopropanol (HFIP), 2,2,2-trifluoroethanol (TFE), formamide or water, the fluorenyl cation, F+, forms by heterolytic C-O bond cleavage. In H2O, the initial (10 ps) spectrum of F+ has lambdamax at <460 nm. This absorption red-shifts with T = 25 ps to the "classical" spectrum with lambdamax = 510-515 nm. This process is assigned to the solvation of the initial "naked" cation, or rather, the contact ion pair. The lifetime of the solvated fluorenyl cation in H2O (or D2O) and TFE was measured to be tau 20 ps and 1 ns, respectively. In solvents of lower polarity such as alkanes, ethers and alcohols, the long-lived (tau 1/2 1 micros) fluorenyl radical, F., (lambdamax = 500 nm) forms through homolytic C-O cleavage. In addition to the radical and the cation, the vibrationally relaxed excited singlet state of FOH is seen with its absorption at approximately 640 nm; its lifetime is strongly dependent on the solvent, from 10 ps for formamide to 1.7 ns for cyclohexane. The rate constant for singlet decay increases exponentially with the polarity of the solvent (as expressed by the Dimroth-Reichardt ET value) or with the Gutmann solvent acceptor number. The relaxation of S1 to S0 is accompanied by homolytic C9-O bond cleavage (except in HFIP, TFE, and water, where S1 is not seen).

Dependence of EXAFS (Extended X-Ray Absorption Fine Structure) Parameters of Iodide Anions in Various Solvents upon a Solvent Parameter

Abstract X-ray absorption spectra of I K-edge have been obtained for iodide ions dissolved in various solvents. Oscillation amplitudes of the extended X-ray absorption fine structure (EXAFS) evaluated from the peak intensities in the Fourier-transform spectra were found to correlate with the Mayer-Gutmann acceptor number (AN) of solvents studied. The correlation is quite similar to that for bromide ions, which has already been reported by the same authors (H. Tanida, H. Sakane, and I. Watanabe, J. Chem. Soc., Dalton Trans., 1994, 2321). Such results confirm that the EXAFS method is not only a tool to determine geometrical structures in liquids, but can also be used for evaluating solute-solvent interaction strength, similarly to AN. The I…O distances in protic solvents and I…C in aprotic solvents were determined to be 3.4—3.5 and 3.7—3.8 Å, respectively. In protic solvents, the larger the AN values, the shorter the I…O distances and the larger the co-ordination numbers of I-, which were determined to be 1—4. In aprotic solvents, the co-ordination numbers of I- were found to be 4—8. It seems that aprotic solvents having two methyl groups in a molecule are able to solvate I- through two methyl groups, which is similar to the conclusion reported for Br-.

Solvent‐ and counterion‐specific swelling behavior of poly(acrylic acid) gels

The collapse of alkali metal poly(acrylate) (PAAM) gels was investigated for various water/organic solvent mixture systems: methanol (MeOH), ethanol (EtOH), 2-propanol (2PrOH), t-butanol (tBuOH), dimethyl sulfoxide (DMSO), acetonitrile (AcN), acetone, tetrahydrofuran (THF), and dioxane. In order to ascertain the counterion specificity in the swelling behavior, four kinds of alkali metal counterions were used: Li+, Na+, K+, and Cs+. Remarkable solvent and counterion specificities were observed for every counterion species and every solvent system, respectively. For example, in aqueous EtOH the dielectric constants (Dcr) at which collapse occurred were in the order PAACs < PAALi < PAAK < PAANa. On the other hand, the Dcr at which PAALi gel collapsed increased in the order tBuOH < dioxane < THF < MeOH < 2PrOH < EtOH < acetone < AcN < DMSO, where the Dcr ranged from about 39 to about 67. This was in contrast to our previous observation for a partially quaternized poly(4-vinyl pyridine) (P4VP) gel, which collapsed in a much narrower Dcr region in similar mixed solvents. The present solvent- and counterion-specific collapses are discussed on the basis of solvent properties such as the dielectric constant and Gutmann's donor number and acceptor number of a pure solvent. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2791–2800, 2000

Isomer Distribution and Stereoselectivity in Electron Transfer Reactions of [Co(dien)2]2+ with Anionic Cobalt(III) Complexes

Abstract The product distribution of the three geometrical isomers and the stereoselectivity of the u-fac isomer in the oxidation of [Co(dien)2]2+ (dien = diethylenetriamine) by optically active anionic cobalt(III) complexes were significantly influenced by the geometrical arragement of the coordinated atoms in the oxidants, reflecting the differences in the stabilization of the precursor assemblies due to the hydrogen bonding interactions between the reactants. Solvent effects on the isomer proportions and the stereoselectivity were examined in water, methanol, ethanol, formamide, dimethylformamide, and dimethyl sulfoxide. The results are explained in terms of the differences in the degree of oxidant-solvent interactions depending on acceptor number of solvents.

Synthesis and properties of [Ru(tpy)(4,4′-X 2bpy)H] + (tpy=2,2′:6′,2″-terpyridine, bpy=2,2′-bipyridine, X=H and MeO), and their reactions with CO 2

A novel type of hydrido complex [Ru(tpy)(4,4′-X 2bpy)H] + (X=H and MeO) was synthesized. The stronger hydridic character of the complexes compared with [Ru(bpy) 2(L)H] + type complexes (L=CO, PPh 3 and AsPh 3) was demonstrated by the relatively high chemical shifts of RuH in the 1H NMR spectra and by higher reactivities with CO 2. The reactions of [Ru(tpy)(4,4′-X 2bpy)H] + with CO 2 occurred at second-order rate constants varying from (4.69±0.02) to (5.51±0.04)×10 −3 M −1 s −1 depending on both solvent and X, giving the formato complexes [Ru(tpy)(4,4′-X 2bpy)(OCHO)] + quantitatively. The rate constant was increased with the increase of solvent acceptor number, and the reaction of [Ru(tpy){4,4′-(MeO) 2bpy}H] + with CO 2 was found to be 3.6 times faster than that of [Ru(tpy)(bpy)H] +. These results suggest that nucleophilic attack of the hydride ligand to the carbon atom of CO 2 is the rate determining step for the formation of the formato complex. The structure of the formato complex [Ru(tpy)(bpy)(OCHO)](PF 6) was determined by X-ray crystallographic analysis.

Solvent- and counterion-specific swelling behavior of poly(acrylic acid) gels

The collapse of alkali metal poly(acrylate) (PAAM) gels was investigated for various water/organic solvent mixture systems: methanol (MeOH), ethanol (EtOH), 2-propanol (2PrOH), t-butanol (tBuOH), dimethyl sulfoxide (DMSO), acetonitrile (AcN), acetone, tetrahydrofuran (THF), and dioxane. In order to ascertain the counterion specificity in the swelling behavior, four kinds of alkali metal counterions were used: Li+, Na+, K+, and Cs+. Remarkable solvent and counterion specificities were observed for every counterion species and every solvent system, respectively. For example, in aqueous EtOH the dielectric constants (Dcr) at which collapse occurred were in the order PAACs < PAALi < PAAK < PAANa. On the other hand, the Dcr at which PAALi gel collapsed increased in the order tBuOH < dioxane < THF < MeOH < 2PrOH < EtOH < acetone < AcN < DMSO, where the Dcr ranged from about 39 to about 67. This was in contrast to our previous observation for a partially quaternized poly(4-vinyl pyridine) (P4VP) gel, which collapsed in a much narrower Dcr region in similar mixed solvents. The present solvent- and counterion-specific collapses are discussed on the basis of solvent properties such as the dielectric constant and Gutmann's donor number and acceptor number of a pure solvent. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2791–2800, 2000

Solvent effect on kinetics of the chloride ion cleavage from anion radicals of 4-chlorobenzophenone

Formal potentials (expressed on the ferrocene scale) for the formation of 4-chlorobenzophenone anion radicals ERX/RX−o as well as for the Cl/Cl− couple increase with the solvent acceptor number but the second dependence is at least twice as strong. However, the rate constant for CCl bond cleavage in these radicals decreases with solvent acidity, indicating that solvation of the leaving anion does not determine the kinetics of cleavage. It is shown that solvent effects on the intrinsic rate constant are dominant and can be described by the Pekar factor, as proposed in the Savéant model.

Design of Long-Lived Ru(II) Terpyridine MLCT States. Tricyano Terpyridine Complexes.

The photophysics of Ru(tpy)(CN)(3)(-) and Ru(ttpy)(CN)(3)(-) (where tpy = 2,2':6',2"-terpyridine and ttpy = 4'-(p-tolyl)-2,2':6,2"-terpyridine) has been studied in detail. The complexes exhibit strongly solvatochromic behavior. Emission energies correlate linearly with solvent acceptor number, consistent with the metal-to-ligand charge transfer (MLCT) nature of the emission and the occurrence of second-sphere donor-acceptor interactions at the cyanide ligands. On the other hand, the correlation of emission lifetimes is clearly biphasic, with a sharp maximum found for solvents of intermediate acceptor number. Such a behavior is explained in terms of competition between a direct deactivation channel and an indirect, thermally activated decay pathway, with relative efficiencies depending strongly on MLCT state energy. A gain of 2 orders of magnitude in lifetime is obtained using the tricyano complexes (Ru(tpy)(CN)(3)(-), tau = 48 ns in DMSO; Ru(ttpy)(CN)(3)(-), tau = 40 ns in CH(3)CN) instead of the corresponding bis-terpyridine species (Ru(tpy)(2)(2+), tau = 250 ps in CH(3)CN; Ru(ttpy)(2)(2+), tau = 860 ps in CH(3)CN). This shows how an appropriate choice of ancillary ligands can be used to improve the properties of photosensitizers containing the Ru(II)-terpyridine chromophoric unit.

Solvent effects of 1,4-benzoquinone and its anion radicals probed by resonance Raman and absorption spectra and their correlation with redox potentials

Resonance Raman (RR) and absorption spectra and cyclic voltammograms were measured for 1,4-benzoquinone (BQ) and its anion radical (BQ-•) in various solvents. The absorption maxima of BQ-• around 440 and 320 nm exhibit a good linear correlation both with acceptor numbers (AN) of solvents and the standard reduction potentials of BQ. The wavenumbers of ν8a (Wilson’s notation, C=C stretch) and ν9a (C–H in-plane deformation) of BQ show linear correlations with the polarizabilities and dielectric constants of solvents, respectively. The ν8a and ν7a (C=O stretch) wavenumbers of BQ-• can be linearly correlated with solvent AN. In addition, the standard reduction potentials of BQ also show good linear correlations with both solvent AN and wavenumbers of ν8a of BQ-•. These results cannot be interpreted by simple hydrogen bonding interactions of carbonyl oxygen with solvent but rather suggest that the π-electrons of BQ-• and BQ serve as an H-bond acceptor, forming novel H-bonds with the solvent. The magnitude of the novel H-bond interaction is estimated to be ca. 7 and ca. 3.5 kcal mol-1 or less for BQ-• and BQ in water, respectively. © 1998 John Wiley & Sons, Ltd.

Solvent effects of 1,4-benzoquinone and its anion radicals probed by resonance Raman and absorption spectra and their correlation with redox potentials

Resonance Raman (RR) and absorption spectra and cyclic voltammograms were measured for 1,4-benzoquinone (BQ) and its anion radical (BQ-•) in various solvents. The absorption maxima of BQ-• around 440 and 320 nm exhibit a good linear correlation both with acceptor numbers (AN) of solvents and the standard reduction potentials of BQ. The wavenumbers of ν8a (Wilson’s notation, C=C stretch) and ν9a (C–H in-plane deformation) of BQ show linear correlations with the polarizabilities and dielectric constants of solvents, respectively. The ν8a and ν7a (C=O stretch) wavenumbers of BQ-• can be linearly correlated with solvent AN. In addition, the standard reduction potentials of BQ also show good linear correlations with both solvent AN and wavenumbers of ν8a of BQ-•. These results cannot be interpreted by simple hydrogen bonding interactions of carbonyl oxygen with solvent but rather suggest that the π-electrons of BQ-• and BQ serve as an H-bond acceptor, forming novel H-bonds with the solvent. The magnitude of the novel H-bond interaction is estimated to be ca. 7 and ca. 3.5 kcal mol-1 or less for BQ-• and BQ in water, respectively. © 1998 John Wiley & Sons, Ltd.