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101.
Ultrasound effects on photochemical reactions, part 1: photochemical reactions of ketones with alkenes 总被引:3,自引:0,他引:3
Ultrasound considerably enhances and simplifies photochemical reaction of cyclohexanone with cyclohexene. The Paterno-Büchi reaction of acetone with ethyl vinyl ether is enhanced by ultrasound and yields a different ratio of cis/trans oxetanes under sonication by comparison with the silent reaction. Sonication appears to affect the first reaction by homogenization of excited intermediates and by quenching the excited triplet state at the second reaction. 相似文献
102.
The reaction of diphenylnitrile imine with 8-substituted-8-azaheptafulvenes is both site and regiospecific and resulted in a mixture of two [8+4]-adducts in high yield. The mechanism of the reaction was investigated. The [8+4]-adducts underwent easily a reversible thermal 1,7-sigmatropic shift involving an sp3 nitrogen centre. Diphenylnitrile imine reacted also with tricarbonyl(8-azaheptafutvene)iron complexes lo give adducts to the CN double bond, the degradative oxidation of which with trimethylamine-N-oxide was investigated. The specificity of the cycloadditions is briefly discussed on the basis of a simple perturbation theory approach. 相似文献
103.
V. Tomašić N. Filipović-Vinceković B. Kojić-Prodić N. Kallay 《Colloid and polymer science》1991,269(12):1289-1294
The precipitation boundary in aqueous mixtures of dodecylammonium chloride (DDACl) and sodium dodecyl sulfate (NaDS) was determined in the absence and in the presence of 1 mol dm–3 NaCl. The structure and the composition of the solid phase was characterized by x-ray and chemical analysis, respectively. Activities of Cl– and Na+ ions in the aqueous phase were measured by ion-selective electrodes. As determined by calorimetry, precipitation is an exothermic process.The DDA·DS precipitate was formed in the equimolar region of the precipitation components. Its crystallographic structure is described. In an excess of sodium dodecyl sulfate, the precipitate incorporated substantial amounts of NaDS, as detected by analyses of both solid and liquid phases. X-ray analysis of the dry sample showed peaks of crystalline NaDS. According to the polarization microscopy of wet samples, one may conclude that liquid crystals, containing an excess of NaDS, are incorporated in the solid DDA·DS phase. The same was found in the case of an excess of DDACl; mixed liquid crystals with an excess of DDACl were incorporated in the solid DDA·DS.Interpretation of the solubility boundary points to the presence of DDA+·DS– ion pairs. Formation of these species at low ionic strengths is characterized by the equilibrium constantK
a
0
106. However, in the 1 mol dm–3 NaCl, the association of DDA+ and DS– ions into pairs is inhibited (K
a
0
0). This finding can be explained in terms of ionic clouds around the charged surfactant heads: if these heads are not in close contact, but separated due to structural effects of the chains, the dense distribution of counterions around them at high ionic strengths may compensate for electrostatic attraction and, thus, inhibit ion-pairing. 相似文献
104.
Mária Mečiarová Janka Podlesná Štefan Toma 《Monatshefte für Chemie / Chemical Monthly》2004,135(4):419-423
Summary. Nucleophilic aromatic substitution reactions with imidazole of haloarenes having strongly electron-withdrawing groups were studied under ultrasonic and microwave irradiations. The course of the SNAr reactions was found to be strongly dependent on the electron-withdrawing properties of the substituents as well as on the leaving ability of the halogen atom. Microwave irradiation allowed to shorten the reaction time and to increase the yields compared with ultrasonic irradiation. 相似文献
105.
A method for determination of equilibrium constants in heme model systems is proposed, based on successive linear regression applied to spectrophotometric titrations. The method is illustrated for bis(dimethylglyoximate) iron(II) complexes with pyridine and 4-cyanopyridine ligands. 相似文献
106.
Francesco Nicotra Luigi Panzal Fiamma Ronchetti Giovanni Russo Lucio Toma 《Tetrahedron letters》1985,26(6):807-808
Methyl 3,4,6-tri-O-benzyl-α-D-glucopyranoside and methyl 3,4,6-tri-O-benzyl-β-D-mannopyranoside were directly obtained by m-chloroperbenzoic acid treatment of (Z)-(2R,3R,4R)-6-methoxy-1,3,4-tribenzyloxy-5-hexen-2-ol. 相似文献
107.
A new composite material constituted by mu-{5,10,15,20-tetra(4-pyridyl)porphyrinato cobalt(iii)}-tetrakis-{chloro-bis-(2,2'-bipyridine)ruthenium(ii)} complex (or CoTRP) and cobalt oxide, exhibiting high stability and sensitivity for the quantification of hydrogen peroxide, was obtained by the electrochemical polymerization of the tetraruthenated cobalt porphyrin in alkaline medium. The optimized experimental conditions for the preparation of the modified glassy carbon electrodes and for analysis of H2O2 were carefully determined. Fast sequential analysis (120 determinations h(-1)) in a wide linear dynamic range (5.0 x 10(-7) mol L(-1) to 2.0 x 10(-3) mol L(-1)), with high sensitivity and low detection limit (2.0 x 10(-7) mol L(-1)), was achieved by using these electrodes and the batch injection analysis (BIA) technique. Such characteristics allied to a good stability were explored for the specific determination of hydrogen peroxide in six commercial cosmetics and pharmaceutical product samples, giving results in excellent agreement with those obtained by the spectrophotometric method. 相似文献
108.
François Piriou Karl Lintner Hung Lam-Thanh Flavio Toma Serge Fermandjian 《Tetrahedron》1978,34(5):553-556
In order to analyze completely the ring conformation of [S]-Proline (l-thiazolidine-4-carboxylic acid) this compound has been synthesized with its Cδ atom enriched at 90% in 13C. The 1H-1H, 13C-1H, 13C-13C vicinal coupling constants measured at several pH values describe well the geometry of the thiazolidine ring. The results suggest that the ring has an average planar conformation only in a narrow range of pH close to the pK of the amine group. Above and below this pH the ring tends to adopt preferentially the Sγendo and Sγexo puckered conformations respectively. It is concluded that a good correlation exists between the value of the dihedral angle ø and the character Sγendo or Sγexo of the ring. 相似文献
109.
110.
Toma L Lescouëzec R Vaissermann J Delgado FS Ruiz-Pérez C Carrasco R Cano J Lloret F Julve M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(23):6130-6145
The preparation, X-ray crystallography and magnetic investigation of the compounds PPh4[Cr(bipy)(CN)4].2 CH3CN.H2O (1) (mononuclear), [[Cr(bipy)(CN)4]2Mn-(H2O)4].4H2O (2) (trinuclear), [[Cr(bipy)(CN)4]2Mn(H2O)2] (3) (chain) and [[Cr(bipy)(CN)4]2Mn(H2O)].H2O.CH3CN (4) (double chain) [bipy=2,2'-bipyridine; PPh4 (+)=tetraphenylphosphonium] are described herein. The [Cr(bipy)(CN)4]- unit act either as a monodentate (2) or bis-monodentate (3) ligand toward the manganese atom through one (2) or two (3) of its four cyanide groups. The manganese atom is six-coordinate with two (2) or four (3) cyanide nitrogens and four (2) or two (3) water molecules building a distorted octahedral environment. In 4, two chains of 3 are pillared through interchain Mn-N-C-Cr links which replace one of the two trans-coordinated water molecules at the manganese atom to afford a double chain structure where bis- and tris-monodenate coordination modes of [Cr(bipy)(CN)4]- coexist. The magnetic properties of 1-4 were investigated in the temperature range 1.9-300 K. A Curie law behaviour for a magnetically isolated spin quartet is observed for 1. A significant antiferromagnetic interaction between CrIII and MnII through the single cyanide bridge [J=-6.2 cm(-1), the Hamiltonian being defined as H=-J(SCr1.SMn+SCr2.SMn] occurs in 2 leading to a low-lying spin doublet which is fully populated at T <5 K. A metamagnetic behaviour is observed for 3 and 4 [the values of the critical field Hc being ca. 3000 (3) and 1500 Oe (4)] which is associated to the occurrence of weak interchain antiferromagnetic interactions between ferrimagnetic Cr2III MnII chains. The analysis of the exchange pathways in 2-4 through DFT type calculations together with the magnetic bevaviour simulation using the quantum Monte Carlo methodology provided a good understanding of their magnetic properties. 相似文献