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 of Tetrahydrothiophene 1,1-Dioxides Fused to Oxazolidin-2-one and Morpholin-2-one Fragments

While developing methods of synthesis of sulfolanes fused through the C³–C⁴ bond to oxazolidin-2- one and morpholin-2-one fragments, the reactivity of cis- and trans-isomeric amino alcohols of the sulfolane series toward a number of cyclizing agents was studied. The cis isomers reacted with dimethyl acetylenedicarboxylate and triphosgene to afford the corresponding morpholin-2-ones and oxazolidin-2-ones, whereas the trans isomers gave rise to open-chain aminofumarates and urea derivatives, respectively. The reactions of both cis- and trans-amino alcohols with oxalic acid derivatives (diethyl oxalate, oxalyl chloride) led to the formation of exclusively acyclic mono- and/or diamides.     

Determination of astaxanthin and astaxanthin esters in the microalgae <Emphasis Type="Italic">Haematococcus pluvialis</Emphasis> by LC-(APCI)MS and characterization of predominant carotenoid isomers by NMR spectroscopy

The oily product ZANTHIN® consists of natural astaxanthin, which is manufactured from the microalgae Haematococcus pluvialis by supercritical CO₂ extraction. An HPLC method was developed to separate all of the components of the complex astaxanthin extract using a C₃₀ column. The separation resulted in different isomers of astaxanthin accompanied by two other carotenoids. The main component consisted of astaxanthin singly esterified with several different fatty acids. C18:3, C18:2, C18:1 and C16:0 were identified as the most commonly occurring fatty acids. Doubly esterified astaxanthin was also found, although in lower concentrations compared to singly esterified astaxanthin. After performing a detailed fatty acid analysis by GC-MS, the peaks from the extract were assigned via HPLC-MS. A trans to cis transmutation of the all-trans compound was performed by thermal treatment in order to obtain an enrichment of cis isomers as the basis for unambiguous identification via NMR experiments. The all-trans as well as the 9- and 13-cis isomers of astaxanthin were characterized in detail by UV/Vis, ¹H, and ¹H,¹H COSY NMR spectroscopy.     

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.     

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 ).     

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.     

Modeling the structure,absorption spectra,and cis-trans isomerization of thiacarbocyanine dyes

The relative stability of the trans-and cis-isomers of 3,3′-diethylthiacarbocyanine (Dye1) and 3,3′-diethyl-9-methylthiacarbocyanine (Dye2)¹, as well as sections of the potential energy surfaces along the internal coordinate of the isomerization reaction, were studied using the density functional theory. Calculation of the minimum energy pathway for the isomerization reaction showed that the barrier for rotation about the C₈–C₉ bond is higher for Dye1 than for Dye2. Local minimums were found for the singlet excited state of the 8,9-cis-and trans-isomers of the dyes. In the case of the trans-isomers, substantial changes in the dye structure do not occur and the local minimum of the excited state corresponds to the geometry of the starting trans-isomers, which favors efficient fluorescence. A search for the nearest local minimum of the singlet excited state of the 8,9-cis-isomers leads to structures, which differ significantly from the starting structures, and the intensity of the S₁ → S₀ transition in those structures appears to be practically zero. The results are in agreement with experimental data on the absorption, fluorescence, and fluorescence excitation spectra of the dyes.     

Influence of Linkage Stereochemistry and Protecting Groups on Glycosidic Bond Stability of Sodium Cationized Glycosyl Phosphates

Energy-resolved collision-induced dissociation (ER-CID) experiments of sodium cationized glycosyl phosphate complexes, [GP _x +Na]⁺, are performed to elucidate the effects of linkage stereochemistry (α versus β), the geometry of the leaving groups (1,2-cis versus 1,2-trans), and protecting groups (cyclic versus non-cyclic) on the stability of the glycosyl phosphate linkage via survival yield analyses. A four parameter logistic dynamic fitting model is used to determine CID_50% values, which correspond to the level of rf excitation required to produce 50% dissociation of the precursor ion complexes. Present results suggest that dissociation of 1,2-trans [GP _x +Na]⁺ occurs via a McLafferty-type rearrangement that is facilitated by a syn orientation of the leaving groups, whereas dissociation of 1,2-cis [GP_x+Na]⁺ is more energetic as it involves the formation of an oxocarbenium ion intermediate. Thus, the C1?C2 configuration plays a major role in determining the stability/reactivity of glycosyl phosphate stereoisomers. For 1,2-cis anomers, the cyclic protecting groups at the C4 and C6 positions stabilize the glycosidic bond, whereas for 1,2-trans anomers, the cyclic protecting groups at the C4 and C6 positions tend to activate the glycosidic bond. The C3 O-benzyl (3 BnO) substituent is key to determining whether the sugar or phosphate moiety retains the sodium cation upon CID. For 1,2-cis anomers, the 3 BnO substituent weakens the glycosidic bond, whereas for 1,2-trans anomers, the 3 BnO substituent stabilizes the glycosidic bond. The C2 O-benzyl substituent does not significantly impact the glycosidic bond stability regardless of its orientation.

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Reactions of Arylenedioxytrihalophosphoranes with Acetylenes: XV.<Superscript>1</Superscript> Reaction of 2,2,2-Tribromo-4,6-di-<Emphasis Type="Italic">tert</Emphasis>-butylbenzo-1,3,2λ<Superscript>5</Superscript>-dioxaphospholedioxaphosphole with Pent-1-yne

2,2,2-Tribromo-4,6-di-tert-butylbenzo-1,3,2λ⁵-dioxaphospholedioxaphosphole reacted with a terminal alkyne, pent-1-yne, to give a mixture of two isomeric 1,2-benzoxaphosphinine derivatives, 6,8- and 5,7-di-tert-butyl-2-bromo-4-propylbenzo-1,2λ⁵-oxaphosphinin-2-oxides, at a ratio of 5.9: 1. The regioselectivity of substitution of oxygen in the dioxaphosphole fragment by carbon differs from that observed previously in the reaction with 4,6-di-tert-butyl-2,2,2-trichlorobenzo-1,3,2λ⁵-dioxaphosphole: the minor isomer was formed as a result of substitution of the oxygen atom in the ortho position with respect to one tert-butyl group of the initial phosphole.     

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

The structural features of 39 mononuclear octahedral d ²-rhenium(V) monooxo complexes (I–ХХХIХ) with oxygen atoms of bidentate-chelating (O,O) acido ligands (Lig) are considered. In 21 complexes (I–ХХI), the O(lig) atoms are both in trans and cis positions to oxo ligands. In the other 18 complexes (XXI–XXXIX), both O(lig) atoms are in cis positions to the O(oxo) ligands.     

Crystal structure of two polymorphs of molybdenyl salicylidene-2-furfuriliminate (HL<Superscript>1</Superscript>) [MoO<Subscript>2</Subscript>(L<Superscript>1</Superscript>)<Subscript>2</Subscript>]

The crystal structures of two polymorphs of molybdenyl salicylidene-2-furfuryliminate [MoO₂(L¹)₂] have been solved by X-ray diffraction. Both complexes crystallize in centrosymmetric and non-centrosymmetric space groups (P2₁/c and Р2₁, respectively) of monoclinic system and have similar structures and close geometric parameters. The Мо atoms have a distorted octahedral coordination to two terminal oxo ligands in cis-positions to each other and two pairs of the oxygen atoms (cis- to О(oxo)) and the nitrogen atoms (trans- to О(oxo)) of two bidentate chelate ligands (L¹)^–.     

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.     

Cycloaddition and chlorotropic transformations in reactions of dichloromethylenetrifluoroacetamide with phosphites

Reactions of dichlormethylenetrifluoroacetamide with triphenyl phosphite, diethylchlorophosphite (o-phenylene)diethylamidophosphite, (o-phenylene)chlorphosphite, and 2-fluoro-3-isopropyl-5-tert-butyl-1,3,2-oxazaphospholine proceeded as cheletropic [4+1]-cycloaddition. The formed λ⁵-1,4,2-oxazaphospholines underwent 1,3-migration of the chlorine atom in C=N–C cyclic triad.     

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.     

Internal rotation potential functions of the acryloyl chloride molecule in the ground (<Emphasis Type="Italic">S</Emphasis><Subscript>0</Subscript>) and excited (<Emphasis Type="Italic">S</Emphasis><Subscript>1</Subscript>) electronic states

The internal rotation potential function of the acryloyl chloride molecule in the S ₀ and S ₁ electronic states was reproduced using systems of torsional vibration levels obtained for its trans and cis isomers by analyzing the vibrational structure of the UV spectrum of the molecule. The kinematic factor F in the S ₀ ground state was calculated including geometric parameter relaxation as a function of internal rotation angle. The torsional potential parameters in the S ₀ state obtained in this work were substantially different from those determined from the infrared Fourier-transform spectrum ignoring the resonance perturbation of the level with v = 3. The form of the internal rotation potential function and the higher stability of the trans isomer (the main isomer) were substantiated by high-level quantum-mechanical calculations.     

Dithiophosphorylation of nerol and geraniol trimethylsilyl derivatives

Reaction of tetraphosphorus decasulfide with О-(cis- and trans-3,7-dimethylocta-2,6-dien-1-yl)-trimethylsilanes affords О,О-bis(cis- and trans-3,7-dimethylocta-2,6-dien-1-yl) S-(trimethylsilyl)dithiophosphates.     

On <Emphasis Type="Italic">Trans</Emphasis>-Resveratrol in Aqueous Solutions

A thermodynamic study on aqueous solutions of trans-Resveratrol (3,5,4′-trihydroxy-trans-stilbene) at 25.00 ± 0.02 °C, in 0.5 mol·dm^?3 NaCl, has been conducted. The protolysis equilibria and the complex formation between trans-Resveratrol and a metal(II), namely Mn²⁺ and Cu²⁺, have been investigated. The experimental method consists of potentiometric, spectrophotometric (absorption and emission) acid–base titrations. The pH range investigated is 2.5 ≤ pH ≤ 13 for the binary system, while for the ternary system it is 2.5 ≤ pH ≤ 6. The results of the graphical and numerical methods adopted indicate, for all the systems investigated, the formation of a predominant Me(II)–trans-Resveratrol mononuclear complex. UV–Vis absorption spectra and desorption/ionization time of flight mass spectra show the occurrence of hydrolytic species exhibiting a higher molecular weight than the Resveratrol molecule, becoming more evident as the pH and the time increased. Moreover, high performance liquid chromatography analysis and infrared spectroscopy of aqueous cis/trans-Resveratrol solutions upon excitation at 300 nm have highlighted a highly fluorescent compound, with absorption maximum at 250 nm, and a blue shift in the fluorescence emission that have not previously been reported.     

Structural features of monomeric octahedral <Emphasis Type="Italic">d</Emphasis><Superscript>2</Superscript>-rhenium(V) monooxo complexes with the oxygen atoms of bidentate chelate (О,S and О,С) acido ligands

Some structural features of 12 mononuclear octahedral d ²-Re(V) monooxo complexes (I–ХII) with the oxygen atoms of bidentate chelate (О,S) acido ligands (Lig) and a similar complex with the oxygen atom of a bidentate chelate (О,С) monoanionic ligand (XIII) have been considered. The O(Lig) atoms are in trans positions to О(oxo) ligands in eleven complexes I–Х and XIII and in cis positions to oxo ligands in two complexes XI and XII. In all the cases, Re–O _trans bonds are longer than Re–O _cis (or Re–O_stand).     

Platinum(II) and platinum(IV) chloro complexes with (<Emphasis Type="Italic">RS</Emphasis>)-1-(4-chlorophenyl)-4,4-dimethyl-3-(1Н-1,2,4-triazol-1-ylmethyl)pentan-3-ol

Platinum(II) and platinum(IV) chloro complexes with (RS)-1-(4-chlorophenyl)-4,4-dimethyl-3-(1Н-1,2,4-triazol-1-ylmethyl)pentan-3-ol (L), namely, cis-[PtCl₂L₂], trans-[PtCl₂L₂], and trans-[PtCl₄L₂], were synthesized. The structures of their coordination cores and the coordination mode of the reagent to the metal ions via the N(4) atom of the triazole ring were determined by electronic, IR, and NMR ¹H and ¹³C spectroscopy. The ratio between treo and erythro diastereomers and the conformation of reagent L in the complexes were established from the complete assignment of signals in their NMR spectra.