Charge transfer spectra of organometallic complexes—IX. Evaluation of solvent effects on the electron donor—acceptor interactions between trimethyltinisothiocyanate and iodine

Charge transfer energies of trimethyltinisothiocyanate—iodine complexes in solution are found to depend on the nature of the solvent. The relationship of these solvent shifts with various solvent properties, and is discussed. Stabilization energies of the excited states in the different solvents are determined using the Onsager theory of dielectrics.     

Solvent interactions in the excited state of non-planar donor—acceptor molecules

In order to probe solute—solvent interactions in the intramolecular charge transfer (TICT) state of 2,6,N,N-tetramethylcyanoaniline (TMCA) fluorescence spectra, quantum yields and lifetimes of this compound were measured in binary mixtures of n-hexane with chlorinated hydrocarbons. An isoemissive point in the fluorescence spectra was observed as the composition of the solvent was varied. Evidence for both clustering of polar solvent molecules around the excited solute and for non-specific long-range interactions with the polar bulk of the solution was found. The properties of the solvent affect primarily the efficiency of non-radiative deactivation. Fluorescence quenching by saturated amines gives good evidence that TMCA emission arises from a highly polar state in both polar and non-polar solutions.     

Solvent effects on electronic absorption spectra of nitrochlorobenzenes,nitrophenols and nitroanilines—II. Studies in polar solvents

A general method for estimating the specific solute—solvent interaction energies (E_s) from analysis of solvent effects on electronic absorption spectra has been outlined. The E_s values for a number of mono- and disubstituted benzenes in a variety of solvents such as water, alcohols, chloroalkanes, ether and acetonitrile have been estimated and the results are discussed in relation to the interacting groups in the solute and solvent molecules. These interactions, which can be classified as H bonding or EDA type, are mainly electrostatic in nature. These studies indicate that, in the case of disubstituted benzenes, the intramolecular electronic interactions are stronger than the solute—solvent interactions.     

Solvent effects on electronic absorption spectra of nitrochlorobenzenes,nitrophenols and nitroanilines—I. Studies in nonpolar solvents

Estimation of dipole moments and polarizabilities in various excited states of o-, m- and p-nitrochlorobenzenes, nitrophenols, nitroanilines and the corresponding monosubstituted benzenes was carried out using solvatochromic shifts in electronic absorption spectra making use of equations based on McRae's and Abe's approaches. Comparison of the observed μ_es with those obtained from addition of group moments indicates that, in o- and m-nitrophenols and o- and m-nitroanilines, the electronic transitions have their origin in the donor groups. The excited states of p-nitrophenol and p-nitroaniline appear to have comparable contributions from the excited states of both the donor as well as the acceptor group due to the large extent of resonance interaction.     

On the extraction of spectra of components from spectra of mixtures. A development in factor theory—II

The theory of factor analysis developed in Part I [A. Muller and D. Steele, Spectrochim. Acta 46A, 817 (1990) [1] is extended to cases where m > 3, m being the number of factors. The effect of increasing the number of independent parameters by m(m-1) for T′ and the subsequent changes produced in the transformed eigenspectra, are investigated. Applications to actual spectra of mixtures of: (A) butan-2-one, ethyl ethanoate, cyclohexane and oct-1-ene (B) butan-2-one, ethyl ethanoate, cyclohexane and 2-methylpentane and (C) oct-1-ene, butan-2-one, ethyl ethanoate, cyclohexane and 2-methyl-pentane are presented. Using standard target techniques, an alternative approach is developed for the m> 3 case. This is based on transformation of the leading three eigenspectra, followed by identification and elimination of a component in a repetitive manner, until completion. The problems associated with the implementation of the Beer-Lambert Law are explored the need for accurate determination of a suitable wavenumber block to ensure the removal of the correct amount of each component, is examined. The ability to recognize at least one of the m component spectra per programme cycle is demonstrated.     

Tautomerism in ketomethylquinolines—IV. The ultraviolet spectra of 2-ketomethylquinolines

Ultraviolet spectral data for a series of 36 2-ketomethylquinolines have been recorded. Members previously shown to be exclusively keto tautomers had spectra closely similar to that of 2-methylquinoline. Most of the rest, which were largely or exclusively in the enaminone forms, showed strong long wavelength absorptions. These are shown to be consistent with cis—s—cis enaminone structures. In aqueous acid, most of the enaminones protonated on carbon and those with electron-withdrawing groups were deprotonated in molar aqueous sodium hydroxide.     

Charge transfer spectra of organometallic complexes—II. Determination of the donor site in trialkyltinhalides

The charge transfer spectra of several trialkyltiniodide- and bromide-iodine systems are presented. Interpretation of the blue shift, the charge transfer band maximum and the formation constant data leads to the conclusion that, on complexation with iodine, the halide atom is the preferred donor site in the trialkyltinhalide molecule.     

Intermolecular interaction in solution—IV. The influence of solvent on the association of proton donors and acceptors

Infrared spectroscopic studies of indole, diphenylamine and tertiary butanol with proton acceptors, diethylacetamide and ethyl acetate show that the solvent used has a strong directive influence on the association. From a consideration of band frequencies and frequency shifts due to association the solvents were arranged according to the effects produced, while a linear correlation was not observed between the spectroscopic measurements on dilterent donor-acceptor systems and the solvents present.     

The vibrational spectra,molecular structure and conformation of organic azides—IX. Azidoethane

A safe method for the synthesis of azidoethane from ethylbromide is given and ¹H and ¹³C NMR data are reported.The i.r. and Raman spectra of azidoethane have been recorded in the region 4000-40 cm⁻¹ and interpreted in terms of two conformers, anti and gauche, present in the vapour and in the liquid and of the gauche conformer in the crystalline solid. Matrix isolation studies reveal the gauche conformation to be the more stable in argon and in nitrogen matrices and probably also more stable in the vapour. The enthalpy difference between the conformers is calculated to be ΔH⁰_a→g (N₂ matrix) ≈ ΔH⁰_a→g (vap.) = −0.56(10) kJ mol⁻¹, and the barrier to rotational isomerism (anti → gauche) as 9.0(10) kJ mol⁻¹ in the nitrogen matrix and less than 6 kJ mol⁻¹ in the argon matrix. Careful Raman studies of the liquid at 140–290 K reveal the gauche conformation to be the more stable in the liquid phase as well, the enthalpy difference being ΔH⁰_a→g (liq.) = − 1.15 (5) kJ mol⁻¹.The majority of the fundamentals for both conformers have been assigned with the aid of normal coordinate calculations using previously developed scaled quantum mechanical force fields which are also presented.     

The vibrational spectra of complexes with planar monothio-oxamides—II. Complexes of N(s)-methylmonothio-oxamide

The new complexes Pd(SH₂)₂ · H₂O, M(SH) · H₂O (M = Ni, Pd, Pt) and M(SH) · 0.5H₂O (M = Cu, Zn), where SH₃ = N_(s)-methylmonothio-oxamide, have been prepared. The complexes were characterized by metal analyses, thermal methods and i.r., Raman and u.v./vis spectroscopic studies. The vibrational analyses of the complexes are given using NH/ND, CH₃/CD₃ and metal isotopicsubstitutions. The Ni(II), Pd(II), Pt(II) and Cu(II) compounds are square planar. The vibrational spectra show that in Pd(SH₂)₂ · H₂O the coordination occurs via the sulphur atom of the deprotonated thioamide group and the oxygen atom of the neutral primary amide group, in a bidentate chelated fashion. The doubly deprotonated SH²⁻ ion behaves as a bridging bis-bidentate ligand giving polymeric structures.     

Theoretical studies on the influence of molecular interactions on the mechanism of electron transfer in photosynthetic reaction center of Rps.viridis

Based on the QM/MM optimized X-ray crystal structure of the photosynthetic reaction center (PRC) of purple bacteria Rhodopseudomonas (Rps.) viridis, quantum chemistry density functional method (DFT, B3LYP/6-31G) has been performed to study the interactions between the pigment molecules and either the surrounded amino acid residues or water molecules that are either axially coordinated or hydrogen bonded with the pigment molecules, leading to an explanation of the mechanism of the primary electron-transfer (ET) reactions in the PRC. Results show that the axial coordination of amino acid residues greatly raises the ELUMO of pigment molecules and it is important for the possibility of ET to take place. Different hydrogen bonds between amino acid residues, water molecules and pigment molecules decrease the ELUMO of the pigment molecules to different extents. It is crucial for the ET taking place from excited P along L branch and sustains that the ET is a one-step reaction without through accessory bacterioc     

Donor and acceptor number effects for the solvatochromic behaviour ofbis-(2,2′-bipyridyl)-bis-cyanoiron(II) in binary aqueous mixtures

Summary Correlation with acceptor numbers was made for the solvatochromic behaviour ofbis-(2,2-bipyridyl)-bis-cyanoiron(II) in binary aqueous mixtures of acetonitrile andDMF. The relationship between isosolvation point and donor number of the organic cosolvent was proved to be linear. Preferential solvation occurs by water in the case of the binary acetonitrile mixtures and byDMF in the case of the binaryDMF, aqueous mixtures.

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Effekte von Donor- und Akzeptor-Zahlen auf die Solvatochromie vonbis-(2,2-Bipyridyl)-bis-cyanoeisen(II) in binären wäßrigen Lösungen

Zusammenfassung Es wurde eine Korrelation zwischen Akzeptorzahl und dem solvatochromen Verhalten vonbis-(2,2-bipyridyl)-bis-cyanoeisen(II) in binären wäßrigen Mischungen von Acetonitril undDMF durchgeführt. Die Beziehung zwischen Isosolvatisierungspunkt und Donorzahl der organischen Kosolventien erwies sich als linear. Bevorzugte Solvatisierung durch Wasser tritt im Fall der binären Acetonitrilmischungen auf, bei den wäßrigenDMF-Mischungen hingegen wird das Substrat bevorzugt durchDMF Solvatisiert.

     

The vibrational spectra of amides—II. The force field and isotopic shifts of N,N-dimethyl formamide

The effects of ¹⁶O → ¹⁸O substitution on the vibrational frequencies of N,N-dimethylformamide have been studied. To understand these and the effects of previously measured shift data due to ¹³C, ²H and ¹⁵N ab initio calculations of frequencies and intensities have been carried out at the 3-21G level. Accord between theory and experiment is generally good. A surprising result is the prediction of a weak band near 2000 cm⁻¹ in DMF due to in-plane interaction between the methyl umbrella modes and the anti-symmetric CN stretch. This abnormally high frequency is explained as arising due to the planar trigonal C₃N entity. Previous problems in reproducing isotope shifts are shown to be due to this mode being previously assigned near 1500 cm⁻¹. The effects of suppressing reference to one of a set of internal valence angles involved in a redundancy are explored. It is shown that the principal effect is to add the diagonal quadratic constant for that coordinate to all other quadratic terms involving pairs of the angles involved in the redundancy. This results in large, almost equal, interaction constants amongst this set. Such effects are seen in the present work. The ab initio field is shown to be compatible with ab initio fields of mono N-methyl amides extant in the literature.     

The vibrational spectra of germane and silane derivatives—XII. A reassignment of the dimethylhalosilanes

The i.r. and Raman spectra of the dimethylhalosilanes, Me₂SiHZ and Me₂SiDX (X = F, Cl, Br, I) have been recorded and the fundamental vibrations assigned. Analysis of the spectra of the deuterated compounds indicate that existing assignments for Me₂SiHX are in error.     

The influence of water on the isomerization of α-pinene in a supercritical aqueous-alcoholic solvent

The influence of water as a cosolvent and catalyst of the isomerization of α-pinene in a supercritical aqueous-alcoholic (ethanol) solvent was studied experimentally. At T = 657 K and p = 230 atm, an increase in the concentration of water in the reaction mixture was found to increase the rate of the reaction and its selectivity with respect to the desired product, limonene. Water exhibited the properties of an acid catalyst because of its ionization. Mathematical experimental data processing was performed to evaluate and separate the contributions of the radical and ionic paths to the total rate of the reactions that occurred during the thermal isomerization of α-pinene.     

On the extraction of spectra of components from spectra of mixtures. A development in factor theory—I

The theory of factor analysis is extended to permit the computer based extraction of the spectra of pure components from spectra of mixtures. A simultaneous linear, non-orthogonal transformation of the eigenspectra and eigenvectors is used to generate all positive absorbances and concentrations within noise level. Applications to actual spectra of mixtures of: (A) ethyl ethanoate, butan-2-one and oct-1-ene; (B) ethyl ethanoate, butan-2-one and cyclohexane; and (C) butan-2-one, cyclohexane and 2-methylpentane are presented. The effects of changes in signs of the constrained diagonal elements of the transformation matrix is investigated. To explore the ability of the software to cope with component spectra in which there are no wavenumbers at which one component dominates an artificial set of mixtures is examined. Recognizable spectra are extracted. It appears that, even when there are no wavenumbers at which one component dominates, the condition of finding “the sum of squares of negative absorbances/concentrations” near zero is adequate to yield useful spectra for library searches.     

Chemical effects of satellites on X-ray emission spectra—II. A general theory of the origin of chemical effects and its application to Cl Kα spectra

A theory is presented to predict the intensity of satellites in the compounds through second order in perturbation theory. It was found that the satellite intensity is proportional to the square of the orbital-relaxation energy. We have applied the theory to the interpretation of chemical effects of K_α parasites—satellites within the natural width of main lines—of Cl compounds. The relaxation energies of the compounds have been calculated with the use of an SCC-DV-X_α MO method. The theory is in good agreement with the experimental results except for CsCl and RbCl. A reason for the exceptions is also presented.     

Solvent effect on the stereoselectivity in cycloaddition of cyclopentadiene to unsaturated esters. Invalidity of the solvent polarity parameter Ω

Solvent effect on the ratio of the endo and exo isomers formed by the Diels-Alder reaction of cyclopentadiene with acrylic acid esters can be described by multiparameter equations involving solvent polarity and electrophilic solvating power as determining parameters. The solvent polarity parameter Ω based on the stereoisomer ratio in the reaction with methyl acrylate cannot be regarded as a universal measure of solvating power, which was demonstrated using a number of examples.     

The influence of the nature of the solvent on the crystal structure and the character of formation of hydrogen bonds inN′-(5-nitrofurfurylidene)isonicotinehydrazide

N(5-Nitrofurfurylidene)isonicotinehydrazide (1) was synthesized in the reaction of nicotinic acid hydrazide with 5-nitrofurfurol in anhydrous or aqueous ethanol. Crystals of different shape and color were obtained depending on the conditions of synthesis and the nature of the solvent. As was established by IR spectroscopy, compound1 in the crystalline state forms solvates of various types. An X-ray study of two different crystals, one obtained by recrystallization from methanol (1a), and the other obtained from aqueous acetic acid (1b), was performed. In the crystal structure of1a intermolecular hydrogen bonds (IMHB) of the NH...N(Py) type occur; the crystals1b are built of solvates with one molecule of acetic acid in which the components are bonded by the IMHB (Ac)O-H..N(Py). The solvates are linked in an infinite chain by the amidohydrate IMHB C=O...W...H-N.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2263–2268, September, 1996.