Showing papers in "Polish Journal of Chemistry in 2007"

On the way to physical interpretation of hammett constants : How substituent active space impacts on acidity and electron distribution in p-substituted benzoic acid molecules

Abstract: Electron distribution was investigated in molecules ofp-substituted benzoic acids by means of Natural Population Analysis. The analysis offers a valuable insight into the impact of a given substituent on the individual atoms' charges in the molecules, on the excess of π electrons in the ring and on the uniformity of their distribution. The more uniform the distribution, measured by means of standard deviation of n electrons amounts localized on individual atoms in the ring, the more acidic is the molecule. On the other hand, an increase of the π electron number in the ring brings about an opposite effect. No correlation was found between the total substituent charges and the Hammett constants. However, a new variable, composed of charges of substituents, added to charges of the ring C ipso atoms, was highly correlated with charges of acidic hydrogens, with the π-electron populations on the individual ring atoms, and eventually, with the Hammett constants. On that basis a notion of the active substituent space was introduced, which comprises the substituent itself and the ring ipso carbon atom. It has been found that it is the charge of the active space, but not the charge of the substituent itself, which is well correlated with the acidity and other properties ofp-substituted benzoic acids.

Is the Aromaticity of the Benzene Ring in the (eta6-C6H6)Cr(CO)3 Complex Larger than that of the Isolated Benzene Molecule?

Abstract: The aromaticity of the benzene ring in the (η 6 -C 6 H 6 )Cr(CO) 3 complex is analyzed using several indicators of aromaticity based on different physical manifestations of this property. All indices used except NICS show that there is a clear reduction of the aromaticity of benzene upon coordination to the Cr(CO) 3 complex. The particular behavior of the NICS index has been analyzed in detail and we have concluded that the reduction of the NICS value in the benzene ring of the (η 6 -C 6 H 6 )Cr(CO) 3 complex is not a manifestation of an increased aromaticity but is due to the ring currents generated by the electron pairs that take part in the benzene-Cr(CO) 3 bonding.

Novel Nanomaterials for Prospective Biomedical Applications: Synthesis, Structure and Toxicity

Abstract: Magnetic nanoparticles, because of their unique properties, are expected to find many prospective applications including data storage, ferrofluids, catalysis, and biomedicine. In this critical review, synthesis methods as well as the characteristics of magnetic nanoparticles are presented. In addition, the benefits and drawbacks of using nanoparticles in biomedical applications are clearly presented.

Hydrogen Bonds in Boronic Acids and Their Complexes

Abstract: The structures ofarylboronic acids, ArB(OH) 2 , are reviewed. These structures are different depending on the substituents in the aromatic ring. The main types of such forms are hydrogen-bonded dimers and chains in which the second B-OH group forms a hydrogen bond with donor atom. Diboronic acids form two-dimensional networks. The presence of an electron donor group in ortho position usually leads to the formation of intramolecular hydrogen bond, but in some cases intermolecular interactions are also observed. Heterodimers with anions ofcarboxylic acids and with amino acids are the stable complexes, in opposite to the complexes with monofunctional Lewis bases.

Preparation and characterization of polysiloxane xerogels having covalently attached phosphonic groups

Abstract: Porous materials with residual phosphonic -P(O)(OH) 2 groups (2.6-3.5 5 mmol·g -1 ) were synthesized by acidic treatment of nonporous xerogels containing =Si(CH2) 2 P(O)(OC2H5)2 functional groups. Elemental analysis, IR and solid-state NMR data clearly show that the structure of the functional layer of such xerogels is stable against further destruction under boiling concentrated HCl for 24 h. Thermal analysis results testify that the functional layer is stable up to 150°C. An increase in the relative quantity of the structure-forming agent (tethraethoxysilane) during the synthesis of initial xerogels results in an increase of a specific surface area of the phosphonic acid-modified xerogels (till 720 m 2 /g). The 31 P CP/MAS NMR data indicate that a part of phosphonic acid groups forms -(HO)(O)P-O-Si≡ linkages during vacuum drying due to phosphonic-silanol groups reaction.

Investigation of the Ho2X3-Cu2X-ZX2 (X = S, Se; Z = Si, Ge) systems

Abstract: Phase equilibria in the Ho 2 X 3 -Cu 2 X-ZX 2 (Z = Si, Ge; X = S, Se) systems at 870 K were determined using X-ray single crystal and powder diffraction. The existence of the HoCuS 2 , HoCu 5 X 4 compounds and the Ho (2+x)/3 Cu 2-x S 2 (0 < x ≤ 0.61), Ho (2+x)/3 Cu 2-x Se 2 (0 ≤ x ≤ 1) solid solutions was confirmed in the Ho 2 X 3 -Cu 2 X (X = S, Se) systems. The Ho 3 Z 1.25 S 7 compounds exist in the Ho 2 S 3 -ZS 2 (Z = Si, Ge) systems. No compounds occur in the Ho 2 Se 3 -ZSe 2 (Z = Si, Ge) systems. The formation of the Cu 8 ZX 6 , Cu 4 GeS 4 and Cu 2 ZX 3 compounds was confirmed in the Cu 2 X-ZX 2 (Z = Si, Ge; X = S, Se) systems. The formation of the Ho 3 CuZX 7 (Z = Si, Ge; X = S, Se) compounds was observed in the Ho 2 X 3 -Cu 2 X-ZX 2 systems.

Gyrolite Formation in CaO–SiO2źnH2O–gamma-Al2O3–Na2O–H2O System under Hydrothermal Conditions

Abstract: The influence of γ-Al 2 O 3 and Na 2 O additives on the gyrolite formation process in the CaO-SiO 2 ·nH 2 O-H 2 O mixture has been examined It has been proved that γ-Al 2 O 3 is not recommended for the synthesis of gyrolite, because Al 3+ ions stimulate the formation ofC-S-H(I) and 113 nm tobermorite (where C - CaO, S - SiO 2 and H - H 2 O), Na 2 O positively affects the formation of gyrolite: this compound is formed already after 8 hours of isothermal curing at 200°C On the contrary, in the pure mixtures gyrolite formed after only 32 h at 200°C In order to compare the cation exchange activity of synthesized gyrolite with (Al+Na)-substituted tobermorite, the ion exchange experiments were employed as a test reaction

Synthesis and Characterization of Novel Phosphorictriamide Derivatives with Morpholine Substituents: Crystal Structures of Substituents: Crystal Structures of (CF3)C(O)NHP(O)(NC4H8O)2 and (p-Br-C6H4)C(O)NHP(O)(NC4H8O)2

Abstract: Using phosphorus pentachloride as a substrate, carbacylamidophosphates of the general formula (R)C(O)NHP(O)(NC 4 H 8 O)2, where R = CH 2 Cl I; CHCl 2 II; CCl 3 III; CF 3 IV; p-Me-C 6 H 4 V; p-Br-C 6 H 4 VI; p-Cl-C 6 H 4 VII, were prepared and characterized by 'H, 31 P and 13 C NMR, IR spectroscopy and elemental analysis. Different carboxylic amides attached to phosphorus nuclei affect on IR and NMR spectra. Three-bond coupling constants between phosphorus and carbon nucleus, 3 J(P,C aliphatic ) in the synthesized compounds, were greater than two-bond coupling constants, 2 J(P,C aliphatic ). The structures of IV and VI were determined by single-crystal X-ray diffraction techniques. The compounds IV and VI formed centrosymmetric dimers via intermolecular N-H···O=P hydrogen bonds.

Structure and Vibrational Spectra of the 1:1 Squaric Acid (H2SQ) – Tetramethylpyrazine (TMP) Adduct

Abstract: The crystal structure of the title complex was determined at 100 K by X-ray diffraction. It consists of double ionized dimeric (HSQ) 2 -2 species and protoned TMP·H + cations. Strong charge assisted (OHO) - and (NHO) + hydrogen bonds are the main factor of crystal packing. A wealth of unconventional C-H…O and C-H…N relatively short bridges should be emphasized. Particularly important are the latter ones binding two adjacent TMPH + cations. The structure is well manifested in the IR and Raman spectra, particularly in the region of v(OH) and v(NH) as well as of v(C=O) frequencies. The complexation ofTMP leads to a marked change in the low and high frequency vibrations of the methyl groups. An anomaly on the DSC runs has been found at 163/175 K (cooling/heating) which can be assigned to the freezing of the methyl group rotations. No change of the crystal symmetry is observed at this temperature.

Crystal and molecular structure of 1: 1 complex between piperidine-3-carboxylic acid and p-hydroxybenzoic acid studied by X-ray diffraction, FTIR, 1H and 13C NMR spectroscopy, and B3LYP method

Abstract: A 1:1 complex between the zwitterionic piperidinium-3-carboxylate (P3C) and/7-hydroxybenzoic acid (HBA), P3C·HBA, has been characterized by single crystal X-ray analysis. The crystals are orthorhombic, space group Pbca, with a = 11.913(1), b = 9.407(1), c = 22.124(2) A. There is a short O-H…O bridge (2.507(2) A) connecting P3C with HBA. The proton is located at the benzoic acid carboxylate but the O-H bond is elongated (1.08 A) and the geometry of the COO groups suggests a nearly equivalent participation in this strong hydrogen bond. The piperidine ring adopts a chair conformation. The bulky carboxylate substituent takes an axial orientation in which it is stabilized by an intramolecular N + -H…O bond (2.880(2) A). In the crystal packing, the P3C-HBA units are connected with crystallographic neighbors by hydrogen bonds that involve only molecules of the same type. In this system of interactions, a zwitterionic molecule attracts two zwitterionic neighbors via its two N + -H 2 donors (accepted by the alternate O atoms of the carboxylate group; 2.823(2) and 2.841(2) A), while an aromatic molecule is connected to another aromatic molecule via a hydrogen bond of length 2.655(2) A, involving the para-hydroxyl donor and the carbonyl acceptor of the carboxylic group. In a model optimized by the B3LYP/6-31G(d,p) method, P3C in its neutral form interacts via a C=O…HOOC hydrogen bond with HBA. The FTIR spectrum shows a broad absorption in the 3100-2400 cm -1 region attributed to vNH and vOH vibrations. The broad absorption in the 1495-910 cm -1 region is attributed to the short 0(3)-H…O(1) hydrogen bond (vOH andyOH). The 'H and 13 C NMR spectra have been analyzed to elucidate the complex structure in solution.

Oxygen solubility in ionic liquids based on 1-alkyl-3-methylimidazolium cations

Abstract: This work presents the results of oxygen solubility in ionic liquids based on l-alkyl-3-methylimidazolium cations. Solubility measurements have been carried out in gasometric apparatus at 22, 50 and 90°C under atmospheric pressure. We report the Henry's constants. In general the occurrence of carbon-fluorine bonds and carbon-hydrogen bonds in ionic liquids (ILs) which can create hydrogen bonds with dissolved oxygen, significantly affects the growth of value of solubility constant K H . Additionally, the stability of ILs towards molecular oxygen was tested. All ILs used in this study were stable in the presence of oxygen and free-radical initiator.

Aminoalkylphosphines, the water-soluble chiral phosphines

Abstract: Chiral water-soluble heterocyclic phosphines 2,2',2"-[1,3,5-diazaphosphinane-1,3,5-triyltris(methyleneimino)]tripropanoic acid (1), 2,2',2"-[1,3,5-diazaphosphinane-l,3,5-triyltris(methyleneimino)]tris(3-phenylpropanoic) acid (2) and 2,2',2"-[1,3,5-diazaphosphinane-1,3,5-triyltris(methyleneimino)]tris(4-methylpentanoic) acid (3) were obtained in reactions oftris(hydroxymethyl)phosphine with chiral amino acids: alanine, phenylalanine and leucine. Course of reaction of amino acids depends on the acidity of solution, at pH ≈ 6 mainly heterocyclic compounds were obtained, however in basic solutions products of Mannich-type condensation 2,2',2"-[phosphinetriyltris(methyleneimino)]tripropanoic acid (4), 2,2',2"-[phosphinetriyltris(methyleneimino)]tris(3-phenyl-propanoic) acid (5) and 2,2',2"-[phosphinetriyltris(methyleneimino)]tris(4-methylpen-tanoic) acid (6) are formed. The prepared compounds were characterized using spectroscopic methods.

UV-Vis and Raman Spectroelectrochemistry of Electrodeposited Polypyrrole in Hexafluorophosphate

Abstract: UV-Vis and Raman spectroscopy are very useful and powerful techniques to characterize the structure of conjugated polymers in various states. Spectroelectrochemical measurements were performed in a three-electrode cell containing polypyrrole (PPY) films as active layers in contact with NaPF 6 aqueous electrolyte. UV-Vis spectroscopy was used to characterize the neutral (undoped) and oxidized (p-doped) states of polypyrrole upon electrochemical p-doping. Raman measurements were done with the excitation wavelengths of 514, 633 and 780 nm. It is shown how the vibrational modes of PPY were influenced by the applied laser wavelength. The neutral form was found to be strongly resonance enhanced with the 514 nm excitation wavelength and the corresponding Raman bands dominate the spectra. Spectra obtained using the 633 nm excitation wavelength displayed a strong contribution of the neutral form, but noticeable bands due to the radical cation and dication were also visible. The spectra recorded using the 780 nm excitation line are dominated by Raman bands of the radical cation and dication.

Preparation of truncated triangular silver nanoparticles by a simple and rapid method in aqueous solution

Abstract: The paper brings details of a simple method for rapid synthesis of triangular silver nanoparticles and their characterization. The method presented proceeds with a simple reaction in aqueous solution at ambient temperature and nanotriangles are synthesized in a few minutes. The formation of triangular nanoparticles was investigated by UV-VIS spectroscopy. Transmission electron microscopy (TEM) images of nanoparticles show that resulting triangles are truncated. The concentration of reactants and pH were found to have influence on the shape of resulting nanoparticles. These results indicate that hydrazine and citrate are necessary for formation of triangular nanoparticles.

Monitoring structural transformations in crystals. Part 10. Monitoring molecular and crystal structures during a yang photocyclization reaction : Comparative studies

Abstract: Structural changes in a crystal, brought about by the Yang photocyclization of the 2-(4-carboxybenzoyl)-2-methyl-endo-bicyclo[211]hexyl salt with (S)-(-)-1-phenyl-ethylamine, were monitored by means of X-ray structure analysis The changes taking place in the reaction centre, as well as changes in molecular orientation and cell constants are discussed Analysis of the geometrical parameters describing the reaction centre enabled an evaluation of the possibility of formation of the opposite enantiomer in a crystal The results are compared with data for other intramolecular photochemical reactions

A Guaianolide Sulfate Conjugate and Other Constituents from Taraxacum alpinum

Abstract: The new guaianolide 8-deacetylmatricarin-8-O-sulfate conjugate in free acid and crystalline sodium salt forms, along with six known sesquiterpene lactones and three known phenolics were isolated from Taraxacum alpinum. The compounds were characterized by chemical and spectral methods. This is the first report on sulfated sesquiterpene lactones from Taraxacum species.

Lignans and Flavonoids from the Seeds of Centaurea bornmuelleri Hausskn. Ex. Bornm. and Centaurea huber-morathii Wagenitz

Abstract: The reversed-phase preparative HPLC purification of the methanol extracts of the seeds of two Turkish endemic species Centaurea bornmuelleri and Centaurea huber-morathii afforded several dibenzylbutyrolactone-type lignans and flavonoids. The lignans arctiin, matairesinol and matairesinoside, and the flavonoid, afzalin, were found in both species. While arctigenin and astragalin were only present in C. bornmuelleri, kaempferol was isolated from huber-morathii. A plant sterol, stigmast-4-en-3β-ol, was also isolated from the dichloromethane extract of C. bornmuelleri. The structures of the isolated compounds were determined by spectroscopic means. The chemotaxonomic significance of these compounds within the genus Centaurea has been discussed.

[2+3]-Cycloadditions of diazoalkanes with imines of hexafluoroacetone and chloral

Abstract: The reactions of N-arylimines 1 and 2 of hexafluoroacetone and chloral, respectively, with diazoalkanes at –60°C to room temperature led to the corresponding 4,5-dihydro-1H-[1,2,3]triazoles 4 and 5, respectively, in a regioselective [2+3]-cycloaddition. The structure of one example in each case has been established by X-ray crystallography. The thermal decomposition of these adducts yielded the corresponding aziridines, bearing two trifluoromethyl and one trichloromethyl group, respectively, at C(2).

Tautomeric Equilibria and pi-Electron Delocalization for the Substrate (Pyruvate) and Inhibitor (Oxamate) of Lactate Dehydrogenase - DFT Studies

Abstract: Keto-enol tautomerism for the substrate (pyruvate) of lactate dehydrogenase (LDH) and amide-iminol tautomerism for its inhibitor (oxamate) were studied at the DFT(B3LYP)/6-31++G(d,p) level. Both anions (and also both radicals) prefer the C=O forms, i.e. the keto and amide form, respectively. The OH forms (enolpyruvate and iminoloxamate) have higher Gibbs free energies. Their amounts in the tautomeric mixtures are larger than 0.01% for anions and lower than 0.001% for radicals. it-Electron delocalization for OCO fragments is greater than that for XCO fragments for both anions and radicals.

Gas-phase Enthalpies of Formation of Tri-, Tetra and Pentachloroanilines: Combined DFT and Experimental Study

Abstract: The gas-phase standard molar enthalpy of formation, at T= 298.15 K, of the 2,3,5,6-tetra-chloroaniline was derived as -(10.6 ± 3.2) kJ·mol -1 from the enthalpies of combustion of the crystalline solid, measured by rotating-bomb combustion calorimetry, and its enthalpy of sublimation obtained by Calvet microcalorimetry. The standard molar enthalpies of formation of all the isomers of the trichloro-, tetrachloro- and pentachloroaniline were calculated by computational thermochemistry based on a Density Functional Theory approach. The calculated values show a good agreement with the experimental results available for some of those isomers.

Synthesis of 1,3-Oxaselenan-2-imines from Isoselenocyanates

Abstract: The reactions ofaryl isoselenocyanates 1 with 3-chloropropan- 1-ol (8) in the presence of sodium hydride in dichloromethane at room temperature gave 1,3-oxaselenan-2-imines 10 in fair yield. A reaction mechanism via nucleophilic attack of the alcoholate at the isoselenocyanate 1, followed by an 6-exo-teτ cyclization, is most likely.

Nucleophilic Cleavage of Selenaheterocyclic Ring in Benzisoselenazol-3(2H)-ones and 1,3,2-Benzodiselenazoles

Abstract: The reactions of cyclic selenenamides: benzisoselenazol-3(2H)-ones and 1,3,2-benzo-diselenazoles 3 with living cell nucleophiles such as water and thiols were investigated. Both of them caused Se-N bond cleavage. The thiolysis of 1 led to selenosulphides 6, 9 or to products of their disproportionation the equimolar mixtures of diselenides 7 and disulphides 8. The hydrolysis of 1 and 3 as well as thiolysis of 3 resulted in formation of corresponding diaryl diselenides 7 or 10.

Cyclic Voltammetric, Chronoamperometric and Quartz Crystal Microbalance Study on Hydrogen Absorption into and Dissolution of Pd and Pd-noble Metal Alloys

Abstract: Hydrogen absorption into and electrochemical dissolution of thin Pd and Pd alloy (Pd-Au, Pd-Rh) layers have been studied in acidic solutions (0.5 M H 2 SO 4 ) with the use of cyclic voltammetry (CV) and chronoamperometry (CA) coupled with the electrochemical quartz crystal microbalance (EQCM). Currents due to hydrogen adsorption and absorption in α- and β-phase are distinguished on CV curves. The amount of absorbed hydrogen depends on electrode potential and increases with the potential decrease. Hydrogen absorbed in Pd-Au and Pd-Rh alloys is oxidized at a lower potential than in the case ofpure Pd. In the case of the Pd-Au system the potential region of phase transition is shifted positively in comparison with Pd indicating higher stability of the β-phase, while for the Pd-Rh system the potential region of phase transition is shifted negatively indicating lower stability of the β-phase. Hydrogen absorption is accompanied by stresses inside Pd crystal lattice, both phenomena affecting the EQCM response. EQCM experiments indicate that the magnitude and distribution of stresses are different for absorption and desorption processes, which seems to confirm the important role of the stress effect in the phenomenon ofabsorption/desorption hysteresis. Pd dissolves electrochemically during polarization to sufficiently high potentials in a CV experiment. The amount of dissolved metal increases with an increase in electrode potential and a decrease in scan rate. Due to Pd preferential dissolution during potential cycling of Pd-Au alloys both cyclic voltammogram and frequency-potential response transform towards curves typical ofAu electrode.

Synthesis, Characterization and Thermal Decomposition of Yttrium and Light Lanthanides with 4,4'-Bipyridine and Dichloroacetates

Abstract: A novel mixed-ligand complexes with empirical formulae: Ln(4-bpy)(CCl2HCOO) 3 ·H 2 O (where: Ln = Y, Ce, Nd, Pr and Eu, 4-bpy = 4,4'-bipyridine) were prepared and characterized by chemical and elemental analysis, IR spectroscopy and conductivity measurements (in methanol, dimethylformamide and dimethylsulfoxide). Analysis of the powder diffraction patterns showed that the obtained complexes are crystalline and isostructural compounds. The thermal properties of complexes in the solid state were studied under non-isothermal conditions in air atmosphere. During heating the complexes decompose via intermediate products to the oxides: Ln 2 O 3 (Y, Nd, Eu), Pr 6 O 1 and CeO 2 . A coupled TG-MS system was used to analyse principal volatile thermal decomposition (or fragmentation) products evolved during pyrolysis of Pr(III) and Nd(III) complexes. In air major profiles for ion currents are observed with m/z = 12, 18, 29, 30, 35, 36, 44, 47 amongst others.

Photophysical Properties of Derivatives of 1H-Pyrazolo[3,4-b]quinoline and 1H-Pyrazolo[3,4-b]quinoxaline

Abstract: The fluorescence behaviour of l,3-diphenyl-1H-pyrazolo[3,4-b]quinoline (PQ1), 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoxaline (PQX1) and 3-methyl-1-phenyl-1H-pyrazolo[3,4-b]quinoxaline (PQX2) has been compared. It has been established that these dyes form exciplexes with N,N'-dimethylaniline (DMA) and p-cyano N,N'-dimethyl-aniline (DMABN) in weakly polar dibutyl ether. The reduction potential of these compounds has been measured by cyclic voltammetry. The different behaviour with respect to intersystem crossing process in pyrazoloquinoline and pyrazoloquinoxalines has been explained in terms of larger energy gap between the first excited singlet state and the higher triplet state having a different symmetry in the former system. This is supported by quantum chemical calculations and it explains the lack of the triplet-triplet absorption bands in the flash photolysis experiments in pyrazoloquinoline system in any solvent.

D-Glucosamine Derivatives as Ligands in Highly Enantioselective Palladium-catalyzed Allylic Alkylations

Abstract: The rigid derivative of D-glucosamine bearing single diphenylphosphino benzoic acid moiety was synthesized and applied as the ligand for the enantioselective allylic alkylations. Best results were obtained for 1,3-diphenylpropenyl acetate (up to 96% ee).

Synthesis of Chiral Odoriferous Oxy-derivatives of 1,5,5-Trimethylcyclohexene

Abstract: Ten racemic and ten enantiomeric pairs of odoriferous compounds, mainly esters, were obtained from isophorone. The starting material, isophorone was reduced to racemic isophorol, which was resolved in pure enantiomers via the lipase catalyzed esterification. The next steps of syntheses, orthoacetic Claisen rearrangement, reduction of esters, esterification of alcohols or their oxidation were carried out with the racemic and enantiomerically enriched (above 98% ee) compounds. The propionates of isophorol (7, 7a, 7b) and 2-(l,5,5-trimethyl-2-cyclohexen-1-yl)ethanol (10, 10a, 10b) possess the most valuable odoriferous properties, useful for cosmetic and food industries.

Synthesis and characterization of copper(II) and nickel(II) complexes of isonitrosoacetophenone 4-aminobenzoylhydrazone

Abstract: Two types of copper complexes as well as an oximate bridged nickel complex with a new tridentate ligand containing a monoxime and hydrazone moieties have been prepared and characterized by elemental analyses, IR, 1 H NMR, UV-VIS and magnetic susceptibility measurements. The reaction of isonitrosoacetophenone 4-aminobenzoyl-hydrazone (H 2 L) with CuCl 2 ·2H 2 O gives the complex [Cu(H 2 L)Cl 2 ] where the ligand acts as a neutral O,N,N-tridentate and the coordination takes place in the keto form. The acylhydrazoneoxime ligand reacts with copper(II) and nickel(II) acetate in the presence of the strong base to produce common bimetal(II) oximato complex, [{M(L)} 2 ] in which two copper(II) and nickel(II) atoms are bridged through two N-O bridges of the oximato ligand to afford a binuclear structure. The effects of varying pH and solvent on the absorption behavior of both ligand and complexes have been investigated.

Tartaronitriles : the Derivatives of Tartaric Acid with a Bent Conformation

Abstract: Conformational preferences ofdinitrile derivatives of(R,R)-tartaric acid were studied by means of NMR, CD and X-ray diffraction techniques. Whereas other derivatives of (R,R)-tartaric acid exist predominantly in an extended (T) or bent (G - ) conformation, (R,R)-tartarodinitriles show pronounced tendency toward bent G + conformation. This is rationalized by the presence of the "gauche effect" involving maximum number of stabilizing interactions between the polar groups within the tartarodinitrile molecule.

Synthesis and properties of azoles and their derivatives. Part LVIII. DFT study on [2+3] cycloaddition of trans-nitroethenes to Z-C,N-diphenylnitrone

Abstract: DFT calculations indicate that the transition states of [2+3] cycloaddition of trans-2-phenylnitroethene to Z-C,N-diphenylnitrone led to 3,4-cis and 3,4-trans 4-nitroisoxazo-lidines are almost perfectly symmetrical. Asymmetry of the transition states appears for the reaction with more 71-deficient trans-2-(trichloromethyl)-nitroethene. Nevertheless, in both cases the formation of azolidine rings occurs in one step. The calculational results correlate well with experimental data.