Trans-cis photoisomerization and photoinduced electron transfer as competitive reactions of 9-etylthiacarbocyanine in binary mixtures

The effect of the composition of the dioxane-water mixture on the ability of 9-ethylthiacarbocyanine to participate in competitive reactions of trans-cis photoisomerization and photoinduced electron transfer was studied. An increase in the dioxane content in the range 0–50 vol % leads to a shift of the equilibrium between the dye dimers and monomers toward the monomers (cis-monomers), which is accompanied by a drop in the yield of the triplet dimer molecules, which appear under the action of a laser flash, and electron-transfer products that are formed via the triplet state of dimers in the presence of methylviologen. With growing the dioxane content in the range 50–80 vol %, a shift of the equilibrium between the cis-and trans-monomers toward the trans-monomers occurs, which is accompanied by an increase in the fluorescence intensity. At the dioxane content above 80 vol %, a further shift of the equilibrium toward the trans-monomers occurs, which is accompanied by a substantial increase in the fluorescence intensity and an appearance under the action of a laser flash of the band of the triplet-triplet absorption of the trans-monomer and the absorption band of the cis-monomer as a result of trans-cis photoisomerization. The trans-monomers in the triplet state participate in the electron-transfer reaction with methylviologen. The intersystem crossing process competes with fluorescence and the trans-cis isomerization reaction, which occurs via the excited singlet state of the trans-monomers.     

Localization of Failures in Structural Order of <Emphasis Type="Italic">trans</Emphasis>-1,4-Butadiene Units in Interdefective Regions of a Butadiene-Nitrile Elastomer Matrix

The fractional free volume of chains passing and incorporated into the ordered structures of segments in trans-1,4-configuration in the copolymers of butadiene and acrylonitrile at different content of acrylonitrile units is calculated in order to determine the localization of order disturbances of butadiene trans-1,4-units. Amorphization of the structure occurs in the immediate vicinity of structural defects of acrylonitrilebutadiene rubbers formed by alternating acrylonitrile and trans-1,4-units of butadiene as well as cis-1,4-and 1,2-isomers of butadiene.     

Kinetic and thermodynamic parameters of hydrogen release during the heterogeneous catalytic dehydrogenation of <Emphasis Type="Italic">cis</Emphasis>- and <Emphasis Type="Italic">trans</Emphasis>-isomers of perhydro-m-terphenyl

Comparative studies on the temperature dependence of the dehydrogenation of cis- and trans-isomers of perhydro-m-terphenyl are performed in a flow catalytic reactor. Rate constants and equilibrium constants of all elementary acts of this reaction are calculated on basis of experimental data using the KINET 0.8 program for the mathematical modeling of the kinetics of complex reactions. The resulting data indicate that perhydro-m-terphenyl cis- and trans-isomers structural differences have no appreciable effect on dehydrogenation.     

Potential function of the internal rotation of a methacrolein molecule in the ground (<Emphasis Type="Italic">S</Emphasis> <Subscript>0</Subscript>) electronic state

The structural parameters of s-trans- and s-cis-isomers of a methacrolein molecule in the ground (S₀) electronic state are determined by means of MP2 method with the cc-pVTZ basis set. Kinematic factor F(φ) is expanded in a Fourier series. The potential function of internal rotation (PFIR) of methacrolein in this state is built using experimental frequencies of transitions of the torsional vibration of both isomers, obtained from an analysis of the vibrational structure of the high-resolution UV spectrum with allowance for the geometry and difference between the energy (ΔH) of the isomers. It is shown that the V_n parameters of the potential function of internal rotation of the molecule, built using the frequencies of the transition of the torsional vibrations of s-trans- and s-cis-isomers of the methacrolein molecule, determined from vibrational structure of the high-resolution UV spectrum and the FTIR spectrum, are close.     

An analysis of the vibrational structure of the UV absorption spectrum of methacryloyl chloride vapor

An analysis of the vibrational structure of the UV spectrum of methacryloyl chloride vapor was performed. The spectrum contained unique information about the torsional vibration levels of the trans and cis isomers in the ground (S ₀) and excited (S ₁) electronic states. 136 absorption bands were revealed, and ～85% of them were assigned. The 0-0 transition frequencies of the trans and cis isomers were found. Several Deslandres tables were constructed for torsional vibrations from 0-0 transition frequencies and “local origins” corresponding to fundamental and combined frequencies of both isomers. Systems of torsional levels up to high quantum number values (v ≈ 6–8) were determined, and the ω_e harmonic frequencies and χ ₁₁ anharmonicity coefficients were calculated for both isometric forms in the ground (S ₀) and excited (S ₁) states. The results were substantially different from those obtained in an analysis of Fourier-transform IR spectra.     

Conformational analysis of 2,4,5-trimethyl-1,3,2-dioxaborinane individual stereoisomers

The study of the conformational isomerization of cis- and trans-isomers of 2,4,5-trimethyl-1,3-dioxaborinane I by means of RHF//STO-3G, 3-21G and 6-31G(d) quantumchemical methods led to the conclusion that its route includes equilibrium between sofa conformers with a different steric orientation of substituents at the C-4 and C-5 ring atoms. These conformers are interconverted through the maxima, the conformations of equatorial and axial 2,5-twist-forms. A comparison between experimental ¹H NMR and theoretical vicinal spin-spin coupling constants was used to determine the quantitative conformational composition of stereoisomers and a value of ΔG ⁰ for conformational equilibrium.     

Synthesis of azamacrocyclic compounds by cyclocondensation of aliphatic α,ω-diamines with acetone

Cyclocondensation of 1,4-diaminobutane and 1,6-diaminohexane with acetone afforded the corresponding 18- and 22-membered trans-azamacrocyclic Curtis compounds in high yield, which contain two azomethine and amine nitrogen atoms. A complex mixture of the products formed containing less than 25% of 16-membered azamacrocyclic cis- and trans-isomers when reacting 1,3-diaminopropane with acetone.     

Synthesis and structure of 1-(buta-1,3-dien-2-yl)pyrazoles and their behavior in Diels-Alder reactions

A convenient procedure has been developed for the synthesis of cis-and trans-isomeric 1-(buta-1,3-dien-1-yl)-1H-pyrazoles by reaction of the corresponding pyrazoles with β-methylacrolein diethyl acetal and subsequent 1,4-cleavage of the nucleophilic substitution products. The behavior of the title compounds in Diels-Alder reactions with maleic anhydride has been studied. According to the ¹H NMR data, 1-(buta-1,3-dien-1-yl)-1H-pyrazole is a mixture of cis and trans isomers. Butadienylpyrazoles having methyl groups in the pyrazole ring do not react with maleic anhydride.     

Calculations of the intrinsic constants of the complexation between Cu(II) and halide ions in solution

Experimental curves of spectrophotometric titration for systems containing mononuclear homoleptic complexes were interpreted in an alternative way involving calculation of the intrinsic constants of binding of the ligand by a central ion with fixed coordination sites. This matrix approach allows one to reduce the number of variables in least-squares optimization of titration curves, describing the formation of complexes [MX _n ] (n = 1–4) via three independent variables (\(\bar K\), ω _cis and ω _trans ) for a square planar geometry and via two variables (\(\bar K\) and ω) for a tetrahedral geometry. Differences in the mutual cis-and trans-influences of coordinated ligands were quantitatively estimated for labile complexes in solution. The method proposed was used to calculate the intrinsic constants of complexation between Cu²⁺ and the chloride ion in methanol from spectrophotometric titration data.     

Analysis of the Vibrational Structure of the <Emphasis Type="Italic">n</Emphasis>–π* Transition in the High-Resolution UV Absorption Spectrum of Methacryloyl Fluoride in the Gas Phase

The UV absorption spectrum of methacryloyl fluoride molecule in the gas phase is obtained in the wavenumber range of 32300–35900 cm^?1. The resolved vibrational structure of this spectrum consists of 153 absorption bands. The assignment of all bands has been made for the first time. Values ν_00trans = 35670.0 сm^?1 and ν_00cis = 35371.1 cm^?1 are determined. The fundamental frequencies for isomers in the S₀ and S₁ states are found. Several Deslandres Tables (DTs) are constructed for the torsional vibration of the s-trans- and s-cis-isomers of the investigated molecule using the NONIUS program. The origins in these DTs correspond to bands attributed to ν₀₀, and to the fundamental frequencies of each isomer in states S₀ and S₁. These DTs are used to determine harmonic frequencies ω_e, anharmonicity coefficients х₁₁, and the frequencies of torsional vibration 0–v transitions up to high values of vibrational quantum number v for s-trans- and s-cis-isomers in both electronic states. The frequencies of torsional vibrations for the s-trans-isomer and the s-cis-isomer in the S₀ state are ν″₁ = 80.9 сm^?1 and ν″₁ = 59.8 сm^?1, respectively. The frequencies for the s-trans- isomer and the s-cis-isomer in the S₁ state are ν′₁ = 134.1 сm^?1 and ν′₁ = 103.6 cm^?1, respectively.     

Comparative reactivity of substituted 1,3-and 1,4-thiasilinane <Emphasis Type="Italic">S</Emphasis>-oxides in the sila-Pummerer rearrangement and inversion of the thiocarbonyl group

The thermal sila-Pummerer rearrangement of diastereomeric 2,3,3-trimethyl-1,3-thiasilinane S-oxides was studied. Introduction of the methyl group in the 2 position of 3,3-trimethyl-3-thiasilinane S-oxide slows down the rearrangement. When heated in CCl₄, the trans isomer (2-Me_eq, SO_eq) converts into the cis isomer (2-Me_eq, SO_ax) which rapidly rearranges into 2,2,7-trimethyl-1,6,2-oxathiasilepane. On the contrary, the isomeric 2,4,4-trimethyl-1,4-thiasilinane S-oxide is thermally stable up to 160°C in DMSO. The inversion at the sulfur atom in 2,3,3-trimethyl-1,3-thiasilinane S-oxides and 2,4,4-trimethyl-1,4-thiasilinane S-oxides under the action of triethyloxonium tetrafluoroborate was studied. The trans isomer of 2,3,3-trimethyl-1,3-thiasilinane S-oxide (2-Me_eq, SO_eq) forms with Et₃O⁺BF ₄ ^? a salt which decomposes in two ways. The first involves recovery of the starting sulfoxide due to Sn2 substitution at the carbon atom of the ethoxy group, and the second, convertion into the cis isomer (2-Me_eq, SO_ax) which rearranges into 2,2,7-trimethyl-1,6,2-oxathiasilepane. Under the same conditions, the cis isomer of 2,3,3-trimethyl-1,3-thiasilinane S-oxide (2-Me_eq, SO_eq) decomposes to form siloxanes. trans-2,4,4-Trimethyl-4-thiasilinane S-oxide (2-Me_eq, SO_eq) under the action of Et₃O⁺BF ₄ ^? convers into the cis isomer (2-Me_eq, SO_ax). The B3LYP/6-311G(d,p) theoretical analysis showed that the thermal inversion at the sulfur atom in the compounds studied has a high energy barrier.     

Synthesis and infrared spectra of stereoisomers of some 2-substituted <Emphasis Type="Italic">p</Emphasis>-(vinyl)phenylcyclopropanes

The IR spectra of the synthesized cis-and trans-stereoisomers of 2-ethoxycarbonyl-(I), 2-carboxy-(II), and 2-hydroxymethyl p-(vinyl)phenylcyclopropane (III) are analyzed. On the basis of the data obtained, the geometric structure of the isolated stereoisomers has been established.     

The internal rotation potential functions of the methacryloyl chloride molecule in the ground and excited electronic states

The systems of torsional vibration levels of the trans and cis methacryloyl chloride isomers in the ground (S ₀) and excited (S ₁) electronic states obtained by analyzing the vibrational structure of the gas-phase UV spectrum were used to reproduce the internal rotation potential functions of the molecule in both electronic states. The kinematic F factor in the S ₀ and S ₁ electronic states was calculated taking into account the relaxation of geometric parameters depending on the internal rotation angle. The internal rotation potential function parameters in the S ₀ state are substantially different from the parameters obtained using the torsional levels of the IR Fourier transform spectrum; at the same time, they are substantiated by quantum-mechanical calculations.     

DFT Study of the Molecular Structure,Conformational Preference,HOMO, LUMO,and Vibrational Analysis of 2-, and 3-Furoyl Chloride

Molecular structure, conformational stability and vibrational wave numbers for the rotational isomers of 2-furoyl chloride and 3-furoyl chloride have been computed using the B3LYP method with the 6-311++G(d,p) basis set. From computations, 2-furoyl chloride was predicated to exist predominantly in cis conformation with cis–trans rotational barrier 40.40 kJ·mol^?1, and 3-furoyl chloride was predicated to exist predominantly in the trans conformation with cis–trans rotational barrier 30.17 kJ·mol^?1. The effects of solvents on the conformational stability of all the molecules in nine different solvents (heptane, chloroform, tetrahydrofuran, dichloroethane, acetone, ethanol, methanol, dimethylsulfoxide and water) were investigated. The integral equation formalism of the polarizable continuum model was used for all solution phase computations. The vibrational wave numbers and the corresponding vibrational assignments of the molecules in C₁ symmetry were examined and the simulated infrared spectra of the molecules are reported. The geometrical parameters, highest occupied and lowest unoccupied molecular orbitals, Infrared intensities, and molecular electrostatic potentials results are reported.     

Excited States of Weak Interacting Complexes of Formaldehyde and Alkali Metal Ions

The electronically excited states of formaldehyde and its complexes with alkali metal ions are investigated with the time-dependent density functional theory (TD DFT) method. Vertical transition energies for several singlet and triplet excited states, adiabatic transition energies for the first singlet and triplet excited states S₁ and T₁, the adiabatic geometries and vibrational frequencies of the ground state S₀ and the first singlet and triplet excited states S₁ and T₁ for formaldehyde and its complexes are calculated. Better agreement with the experiment than that of the CIS method is obtained for CH₂O at the TD DFT level. The nonlinear C=O?M⁺ interaction in the excited states S₁ and T₁ is weaker than the linear interaction in the ground state. In the S₀ and S₁ states, the C=O bond is elongated by cation complexation and its stretching frequency is red-shifted, but in the T₁ state the C=O bond is shortened and its frequency is blue-shifted.     

Spectral and kinetic investigation of interaction of 3,3′-diethyl-9-chlorothiacarbocyanine perchlorate with DNA

Interaction of the meso-substituted carbocyanine dye 3,3′-diethyl-9-chlorothiacarbocyanine (DCTC) perchlorate with DNA in phosphate buffer solutions (pH 7) was studied by spectral and kinetic methods. It was shown that the dye mainly exists in the cis-isomer form in water and aqueous-alcoholic solutions. The interaction with DNA leads to the formation of a trans-DCTC complex, which gradually (over a few tens of minutes) converts into the complex of the dye cis-isomer. It was revealed that the reactant concentration and ionic strength of solution have a considerable effect on the kinetic characteristics of trans-cis-reorganization of DCTC complexes, thus indicating a complex character of the process.     

Structural features of monomeric octahedral <Emphasis Type="Italic">d</Emphasis><Superscript>2</Superscript>-rhenium(V) monooxo complexes with oxygen atoms of bidentate-chelating neutral and acidic ligands (O,P)

The structural features of 38 mononuclear d ²-Re(V) octahedral monooxo complexes (I–XXXVIII) with oxygen atoms of bidentate-chelating (O, P) ligands (L ⁿ ) are considered. The atoms O(L ⁿ ) are mostly in trans positions to O(oxo) ligands. In three compounds of general formula [ReO(L_mono)(L ⁿ )₂] (XXXVI–XXXVIII), the O atoms of two L ⁿ ligands occupy both trans and cis positions to oxo ligands. In one complex, namely, in [ReO(L ⁿ )(L _tri ¹¹ )], n = 3 (XXXV), the atom O(L³) is in the cis position to the oxo ligand; the trans position to O(oxo) is occupied by the atom O(L _tri ¹¹ ).     

<Emphasis Type="Italic">Ab initio</Emphasis> quantum-chemical calculations of the energies and structures of 1,2-acetylenedithiol isomers

Ab initio quantum-chemical calculations of 1,2-acetylenedithiol isomers were carried out. The MP2(full), DFT(B3PW91, MPW1PW91), G3, G3B3, and CBS-Q methods were used. According to the calculations, the most stable isomers were 1,2-dithiet, thiiranethione, and trans-1,2-dithioglyoxal. The necessity of including basis set functions with a large angular momentum in calculations was confirmed. The relatively high stability of 1,2-dithiet was attributed to the aromaticity of its four-membered ring. It was noted that the carbon-carbon bond in the three-membered rings of the cis- and trans-isomers of thiirenethiols was unusually short.     

Specifics of deactivation processes of excited states of thiacarbocyanine dyes adsorbed on cellulose

Spectral and kinetic study on deactivation processes of electronically excited states of molecules of cationic (Dye1, Dye2 and anionic (Dye3–Dye5) thiacarbocyanine dyes adsorbed on cellulose was performed. Adsorption of the dyes leads to an increase in the concentration of dimers. The dimers of adsorbates of Dye3–Dye5 exhibit only phosphorescence, whereas the monomers of the adsorbates are capable of both phosphorescence and delayed fluorescence. Adsorbates of Dye3–Dye5 prepared from water and methanol exhibit phosphorescence of cis-monomers. Adsorbates of Dye1 from water and ethanol as well as adsorbates of Dye2–Dye5 from chloroform exhibit delayed fluorescence of trans-monomers. Phosphorescence and delayed fluorescence are observed at room temperature in the presence of air oxygen.     

Vibronic spectra,ab initio calculations,and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part V: Oxalyl chloridefluoride (COCl–COF)

The structure and conformational dynamics of the COCl–COF molecule in the ground and lowest excited electronic states were investigated theoretically by the CASPT2/cc-pVTZ method. The equilibrium geometric parameters, harmonic vibrational frequencies, potential functions of internal rotation, and adiabatic transition energies were obtained. According to the results of calculations, the molecule in the ground electronic state exist as the trans and gauche (dOCCO ~30–40°) conformers with a low potential barrier to gauche–gauche transition therefore it is impossible to exclude existence of the cis conformer (instead of gauche) with a very broad and flat potential minimum. For all the investigated excited electronic states of oxalyl chloridefluoride molecule calculations predicted the trans and cis conformers. The strong coupling of internal rotation around the C–C bond and non-planar vibrations of carbonyl fragments was found for the excited electronic states. The results of calculation were utilized for reanalysis of experimental \( \tilde{A}^{1} A^{\prime \prime} \leftarrow \tilde{X}^{1} A^{\prime} \) and \( \tilde{a}^{3} A^{\prime \prime} \leftarrow \tilde{X}^{1} A^{\prime} \) vibronic spectra reported in Kidd and King (J Mol Spectrosc 50:209–219 (1974), and ibid. 48:592–599 (1973)). The vibrational assignment that does not contradict the vibrational spectroscopy data and results of calculations was obtained.