Réactivité des cinnamoyl-3 pyrones-2 vis à vis des amines primaires

The reaction of primary amines (methylamine, isopropylamine, benzylamine) in neutral medium, on 3-cinnamoyl-2-pyrones gave 7-amino-3,5-dioxo-l,6-octadienes 2 . The formation of these compounds is presumed to occur via nucleophilic attack of amines with a ring opening reaction followed by decarboxylation. Their structures were determined unambiguously by ¹H, ¹³C nmr spectroscopy, elemental analysis and mass spectrometry.     

Addition dipolaire-1,3 aux olefines portant une substitution captodative: reactivite comparee des α et des β amino acrylnitriles vis a vis des arylazides.

Arylazides reacted with α amino-acrylonitriles $\text{1}$ to produce 1-aryl-5-amino-triazoles, and with β amino-acrylonitriles $\text{2}$ to give 1-aryl-4-cyanotriazoles. Kinetics showed the Hammett ρ to be > o and therefore, these reactions are controlled by LUMOazide-HOMOolefin interaction. Despite the captodative substitution in $\text{1}$ and $\text{2}$ (ΔΔ E^≠～ 500 cal.M^?1) does'nt agree with a diradical intermediate.     

Hydroboration d'amines insaturees: XI. Regio- et stereoselectivite des hydrures du bore vis a vis d'amines propargyliques N-phosphorylees

The regioselectivity and the stereoselectivity of the hydroboration of N-alkylallylphosphoramide was examined. This study shows the preferential formation of γ-boron derivatives (90 to 100%) and the excellent stereospecificity of the reaction (100% (Z) configuration).The P^IV-N bond hinders the nitrogen-boron coordination which is responsible for the anomalous behavior of N-propargylic amines towards hydroboration and allows the same regio- and stereo-selectivity as for alkynes. The iodination of boron derivatives leads, with good yields, to N-phosphoryl-β-ethylenic amines.     

Etude de la reactivite de lion azoture vis á vis de cations heterocycliques-IV comportement vis á vis de cations chromylium diversement substitues. Rearrangement thermique des azides covalents obtenus. Voie originale d'acces aux benz[f]heteroazepines

The study of the azide nucleophile reaction with substituted chromylium salts is presented. When heated, the azido 2H-and azido 4H-chromenes obtained give benz(f)oxazepins in very good yields. This is an easy preparation of these compounds.     

Reactivite des imines vis a vis d'alcenes gem disubstitues : Synthese d'aza-1 bicyclo (2,1,0) pentanes

Imines undergo 1,3 dipolar cycloadditions reactions as well as 3^- +2 polar cycloadditions reactions with alkenes substituted at the same carbon atom with an electron withdrawing group and a leaving group to give heterocyclic compounds.     

Reactivite de silanes propargyliques α-fonctionnels vis a vis des derives carbonyles : preparation d'alcools-ethers,de diols et de dioxannes alleniques.

Type 1 functional propargyltrimethylsilanes react with carbonyl derivatives, in the presence of titanium tetrachloride or tetra-n-butylammonium fluoride, to produce allenic alcohols-ethers, diols and dioxanes.     

Etude de la reactivite de l'ion azoture vis á vis de cations heterocycliques-III: Rearrangements thermiques et photochimiques des azides covalents resultant de l'attaque de l'ion azoture sur des cations pyrylium et thiopyrylium diversement substitues. nouvel acces à des heteroazepines

Azidopyrans rearrange at room temperature to 1,3-oxazepins but azidothiopyrans need heating to form unstable thiazepins. These intermediate thiazepins give the competitive formation of the corresponding pyridines after sulphur extrusion or of the corresponding thiophens after elimination of benzonitrile.Photochemical attempts to obtain thiazepins from azidothiopyrans were unsuccessful.     

Comportement d'esters α-ethyleniques vis a vis du systeme Me3SiCl/magnesium/HMPT

The action of the Me₃SiCl/Mg/hexamethylphosphoric triamide system on α-ethylenic esters can follow three pathways: C-silylation (on the carbonatom situated in the β-position with respect to the ester moiety), reductive duplication or simple reduction. Besides the C-silylation, the synthetic interest of this work consists in the facility of preparing, in numerous cases, ?-diesters and also ?-diacids, from the corresponding α-ethylenic monoesters.     

Calibration of UV–vis spectrophotometers for chemical analysis

The spectrophotometer has become the workhorse for high-throughput routine testing for a wide variety of analytes in chemical and biochemical analysis laboratories. It is important for accuracy and reproducibility in measurement that this instrument is correctly set up and calibrated, a task which is facilitated by an understanding of the principles employed. This presentation reviews the principal issues involved: absorbance calibration, wavelength calibration, and checks for both heterochromatic and isochromatic stray light. Methods and materials for making these checks are compared and discussed.Presented at the CITAC Workshop on Traceability and Uncertainty, Wellington, New Zealand, 3–5 May 2004.     

Electrode Kinetics and Complex Formation of [Zn‐Antibiotics‐Cephalothin] System vis a vis Kinetics of Electrode Reactions

Charge transfer reactions between a dropping mercury electrode and a [Mn‐antibiotics‐cephalothin] system were studied at pH = 7.30 ± 0.01, μ = 1.0 MNaClO₄ at 298 K. The antibiotics were doxycycline, chlortetracycline, oxytetracycline, tetracycline, minocycline, amoxicillin and chloramphenicol used as primary ligands and cephalothin as secondary ligand formed 1:1:1, 1:1:2 and 1:2:1 complexes with Zn². Electrode kinetics was discussed on the basis of kinetic parameters viz. transfer coefficient (α), degree of irreversibility (λ), diffusion coefficient (D) and rate constant (k). The values of α varied from 0.40 to 0.57 (0.50) confirm that ‘transition state’ behaves between reactant and product response to applied potential and it lies always between d.m.e. and solution interface. A small variation in potential affects the rate and rate constant greatly.     

Cytotoxic pyranonaphthoquinones from Melloa quadrival vis (Bignoniaceae)

Three new pyranonaphthoquinones: 5-hydroxy-6-methoxy-alpha-lapachone, 5,6-dihydroxy-a-lapachone and 4',5-dihydroxy-6-methoxy-alpha-lapachone, and two known compounds: lapachol and 5,5'-dihydroxy-3',4',7-trimethoxyflavanone, were isolated from the stem bark of Melloa quadrivalvis. Their structures were established by spectrometric data, mainly 1D- and 2D-NMR and mass spectra. The methylazoetetrazolium (MTT) method using viable cells of the strain Hep2 and the strain NCIH-292 demonstrated cytotoxic activity. The CI50 was also calculated. The chloroform extract and 5-hydroxy-6-methoxy-alpha-lapachone inhibited cell growth.     

Reactivite du tetraallyletain et d'allyltrialkyletains vis a vis d'aldehydes,de cetones et d'epoxydes

Tetraallytin reacts readily with non activated ketones and exothermically with aldehydes contrary to other allylic organotins such as allytributyltin. Homoallylic alcohols are obtained after acidolysis of the adducts. Upon extended heating, allylic organotins and epoxides form products which correspond to additon products of isomeric carbonyl compounds. However, starting from cis- and trans-1-phenyl-1,2-epoxypropanes, direct regiospecific but non-stereospecific ring opening is observed with poor yields.     

Reactivite d'organometalliques vis a vis des enynes conjugues α, α'-bifonctionnels: III. Enynes a groupement alcool en α de la triple liaison: Synthese d'allenes et de dienes mono- ou bifonctionnels

Organolithium, organomagnesium and organozinc compounds react with α,α'-difunctional enynes: HOCH₂CCCHCHCH₂Y (Y  OH, OCH₃, N(CH₃)₂). This reaction produces one or two derivatives, according to the nature of the metallic group: mono- or di-functional allenes, mono- or di-functional dienes.     

The rapid identification of organic colorants by UV/vis spectroscopy

A rapid UV/vis spectroscopic method for the identification of organic colorants by the use of Gaussian analysis is presented. Sets of parameters are obtained for the screening with a low number of data. An optical distance using line positions and intensities is defined as a measure for the similarity of UV/vis spectra.     

On the TD-DFT UV/vis spectra accuracy: the azoalkanes

Using an ab intio TD-DFT approach systematically accounting for the molecular surroundings effects, we have computed the n → π* absorption wavelength of 22 azoalkane derivatives. For the complete set of molecules, we propose a theoretical procedure able to reproduce the major auxochromic effects, and to deliver a mean absolute error of 5.8 nm (0.056 eV) with maximal deviations limited to 21 nm (0.20 eV). The impact of including in the model explicit solvent molecules is discussed as well. This contribution confirms that PCM-TD-PBE0 is a first-grade method for simulating the vertical absorption spectra of organic dyes.     

Ion-beam irradiation effects on polyimide-UV–vis and infrared spectroscopic study

Ion-beam irradiation effects on polyimide, Kapton™, were studied with respect to optical and electronic properties. Stack films of Kapton™ (12.5 μm thick) were irradiated to various ion beams in air or vacuo at room temperature and subjected to ultraviolet–visible (UV–vis) spectroscopy, and change in absorbance and energy gap is discussed. The UV–vis absorption spectrum, which is assigned to the transition of electrons in benzene rings from π to π* orbital, upon He²⁺ (6 MeV/u) irradiation in air, shifted towards longer wavelength direction for all cases, and the shift was more obvious for higher linear energy transfer (LET) ion beams. The energy gap of the transition was estimated, and the H⁺ and He²⁺ ion beams caused little change in the transition energy gap Eg, while the heavier ions such as C⁶⁺ and Si¹⁴⁺ caused more significant decrease. This decrease is assumed to the structural changes around benzene rings, and the infrared spectroscopy revealed breakage in imide groups next to benzene ring in the repeating unit of polyimide.     

Reproduction and interpretation of the UV–vis spectra of some flavonoids

The UV–vis spectra of 15 naturally occurring flavonoids, including flavones, flavonols, and isoflavones, were simulated and compared to literature experimental results. For this purpose, the TDDFT method in conjunction with the B3LYP-D3 and B3LYP functionals was applied. In spite of some discrepancy between the structural predictions, the differences between the TDDFT/B3LYP and TDDFT/B3LYP-D3 results are negligible. The performance of both functionals in reproducing the UV–vis spectra of the selected flavonoids is satisfactory. The NLMO clusters, i.e. molecular moieties characterised with distinguished electron density, were created. The combined results from the TDDFT and NLMO approaches were employed to perform deep analysis of the spectra. It was found that the transitions from the bonding NLMO clusters to the LUMO cluster are favoured at longer wavelengths, whereas the transitions from the HOMO and HOMO?1 clusters to the antibonding NLMO clusters are favoured at shorter wavelengths. All flavonoids show the HOMO → LUMO and HOMO?1 → LUMO transitions at long wavelengths, and majority of them show the HOMO → LUMO+1 transition at moderate wavelengths. This investigation confirms our earlier finding that the TDDFT and NBO approaches are complementary, implying that the results from the two theories can be combined to better understand the redistribution of electron density upon excitation.     

Imines et enamines stanniques : IV. Protolyse: synthese d'enamines secondaires; structure,isomerisation, reactivite vis a vis de l'acrylonitrile

The partial protolysis of organotin imines—enamines leads to organic secondary enamines, which we found to be stable in completely aprotic media.Their structure was determined by IR and NMR methods, and their reactivity towards acrylonitrile studied. The results show a much greater reactivity for enamines, as compared to that of the corresponding imine tautomers.     

Study of carbonaceous clusters in irradiated polycarbonate with UV–vis spectroscopy

The formation of carbonaceous clusters in ion‐irradiated polymer films was investigated extensively. Information about these clusters may be obtained with ultraviolet–visible (UV–vis) spectroscopy. The optical band gap (E_g), calculated from the absorption edge of the UV spectra of these polymers, can be correlated to the number of carbon atoms (N) in a cluster with the modified Tauc equation. The structure of the cluster is also related to E_g; for example, a six‐membered‐benzene‐ring‐type structure has an E_g of ≈5.3 eV, whereas a buckminsterfullerene‐type structure has an E_g of ≈4.9 eV. These clusters are responsible for the electrical conductivity in these films. In this work, polycarbonate films (20 μm thick) were irradiated with 45‐MeV Li ions at fluences of 1 × 10¹² to 1 × 10¹³ cm⁻² and were characterized with UV–vis spectroscopy and impedance measurements. The E_g values, calculated from the absorption edge in the 280–315‐nm region with the Tauc relation, varied from 4.39 to 4.35 eV for the pristine and various irradiated samples, respectively. The cluster size showed a range of 60–62 carbon atoms per cluster. The sheet conductivity (σ_dc) and loss (tan δ) values of 10⁻¹⁶ Ω⁻¹cm⁻¹ and 10⁻³ for the pristine sample changed to 10⁻¹⁵ Ω⁻¹cm⁻¹ and 10⁻², respectively, for the irradiated samples. This increase in the values of σ_dc and tan δ may be correlated to the increase in the size of the carbonaceous clusters. This study provides insight into the mechanism of electrical conductivity in irradiated polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1589–1594, 2000     

UV–vis photodegradation of dyes in the presence of colloidal Q-CdS

The interaction of the dyes Safranin-O (SO) and Orange II (OII) with aqueous colloidal Q-CdS clusters, which emit single fluorescence bands with maximum wavelengths at 481 nm (excitonic band) or 559 nm (trapped band), has been studied. This was carried out by monitoring both the photodegradation of the dye in the presence of the clusters and the quenching of the clusters fluorescence by the dyes. The photolysis experiments were carried out by excitation either at 520 nm (the wavelength at which the dyes, but not the clusters absorb light) or at 350 nm (the wavelength at which the clusters strongly absorb light, and the dyes have absorbance minima). At 520 nm, photodegradation of SO could be observed, which follows a first-order kinetics (for trapped-band clusters) and a second-order kinetics (for excitonic-band clusters). For the excitation wavelength of 350 nm, photodegradation of either of the dyes could not be observed. The Stern–Volmer plots for the quenching of the excitonic band-clusters fluorescence by SO show an upward curvature, pointing to the occurrence of more than one species acting as the fluorescence quencher, whereas the Stern–Volmer plots for the quenching of the trapped band-clusters fluorescence by SO are linear, indicating that only one species acts as a fluorescence quencher. Lambert–Beer type plots (absorbance vs. concentration) are linear for SO in water and in trapped band-clusters solutions, but a similar study of SO in excitonic band-clusters solution show the occurrence of a new band, which can be assigned to a ground-state dimer of the dye. The latter can be used to explain both the upward curvature of the Stern–Volmer plots and the second-order kinetics observed for SO photodegradation in the SO-excitonic band-clusters system. The Stern–Volmer plots for the quenching of both fluorescence bands by OII are linear.