Hydrolyse acide du p-nitrophényl-diazométhane dans les mélanges H2O?D2O: analyse des effets isotopiques

The velocity of the hydrogen ion catalysed hydrolysis of p-nitrophenyl-diazo-methane (I) has been measured in H₂O? D₂O mixtures, giving an isotopic α_i = 0.49. The product isotope effect r = 5.1, determined from product analyses, combined with the (overall) solvent isotope effect k_H/k_D = 2.81, yields the primary kinetic isotope effect (k_H/k_D)^I = 3.8, and the secondary kinetic isotope effect (k_H/k_D)^II = 0.75. The CICH₂COOH-catalysed hydrolysis of I in H₂O? D₂O mixtures gave a straight-line plot of k_n/k_H versus the atomic fraction n of deuterium. With four carboxylic acids, as catalysts, values of about 4.3 for the kinetic (overall) isotope effects were observed.     

Influence de l'imidazole,de quelques sels métalliques et de mélanges imidazole/sel métallique sur des réactions de condensation «prébiotiques» induites par les polyphosphates en milieu aqueux

Influence of imidazole, metal salts and mixtures of imidazole/metal salt on ‘prebiotic’ condensation reactions induced by polyphosphates in aqueous solutions In the presence of imidazole, aqueous solutions 0.1 M in glycine and 0.1 M in sodium trimetaphosphate, at pH 8.0–8.6 and room temperature, yield after 14 days up to 3% of triglycine. Addition of Cd²⁺ or Zn²⁺ decreases the yields, while Mg²⁺ increases them slightly. The significance of the systems trimetaphosphate/imidazole and trimetaphosphate/imidazole/magnesium salt in the promotion of ‘prebiotic’ condensation reactions in aqueous solutions, especially the condensation of amino acids, is discussed.     

Polymérisation anionique des diènes. V. Configurations des oligopolyisoprènyl–lithium en milieu benzènique et en présence de dioxanne. Étude par résonance magnétique protonique: Haute résolution (RMP-HR)

By PMR, three dioxane–Li⁺ complexes have been detected for the oligopolyisoprenyl–lithium–dioxane mixtures in benzene solution. The (4-1) living end isomerizes into the cis configuration when the sample temperature or the dioxane concentration is increased, but the isomerization phenomenon is reversible only if dioxane/Li⁺ ratios are smaller than unity. The specificity of the vinyl addition (86%), mainly (4-3) (70%), due to the stronger negative charge at the C_γ carbon atom is effective only at low temperature (+15°C). At higher temperature, because of the steric hindrance of the methyl group, this stereospecificity decreases.     

Solvent effects on the rate of reaction of Cl2˙− and SO4˙− radicals with unsaturated alcohols

Rate constants have been measured in several aqueous/organic solvent mixtures for the addition reaction of Cl₂^˙? radicals with 2-propen-1-o1 and 2-buten-1-o1 as a function of temperature and with 2, 3-dimethyl-2-butene at room temperature. The rate constants were in the range of 10⁶–10⁹ L mol^?1 s^?1, the activation energies were relatively low (1–10 kJ mol^?1), and the pre-exponential factors varied over the range log A = 7.9 to 9.4. The rate constants (k) decreased (by up to a factor of 30) upon increasing the fraction of organic solvent and log k correlated linearly with the dielectric constant for a given water/organic solvent system, but the lines for the different solvent systems had different slopes. A better correlation of log k was found with a combination of the solvatochromic factor, E_T(30), and the hydrogen-bond donor acidity factor, α. This suggests that the rate of reaction is influenced by the solvent polarity and also by specific solvation of the ionic reactant and product. Solvent effect on the reaction of SO₄^˙? with 2-propen-1-o1 was studied for comparison. © 1993 John Wiley & Sons, Inc.     

Etude par Résonance Magnétique Nucléaire de dérivés anthracéniques: II—Anisotropie magnétique du phényle et effets steriques

The peri effect induced by the phenyl group has been studied in the anthracene series by means of ¹H and ¹³C n.m.r. The chemical shifts of overcrowded protons can be explained by a combination of magnetic anisotropy and steric effects. Steric contributions amount to c. 25% of the phenyl induced shift at the peri position. Amongst published ring-current theories, only the model of Johnson and Bovey is capable of describing correctly the shielding region of the phenyl group. The unexpected shieldings and deshieldings, observed by ¹³C n.m.r. in the case of very hindered derivatives, is probably due to distortions of the anthracene skeleton.     

Effect of the Media on the Quantum Yield of Singlet Oxygen (O2(1Δg)) Production by 9H‐Fluoren‐9‐one: Solvents and Solvent Mixtures

We have investigated the effect of a series of 18 solvents and mixtures of solvents on the production of singlet molecular oxygen (O₂(¹Δ_g), denoted as ¹O₂) by 9H‐fluoren‐9‐one (FLU). The normalized empirical parameter E derived from E_T(30) has been chosen as a measure of solvent polarity using Reichardt's betaine dyes. Quantum yields of ¹O₂ production (Φ_Δ) decrease with increasing solvent polarity and protic character as a consequence of the decrease of the quantum yield of intersystem crossing (Φ_ISC). Values of Φ_Δ of unity have been found in alkanes. In nonprotic solvents of increasing polarity, Φ_ISC and, therefore, Φ_Δ decrease due to solvent‐induced changes in the energy levels of singlet and triplet excited states of FLU. This compound is a poor ¹O₂ sensitizer in protic solvents, because hydrogen bonding considerably increases the rate of internal conversion from the singlet excited state, thus diminishing Φ_Δ to values much lower than those in nonprotic solvents of similar polarity. In mixtures of cyclohexane and alcohols, preferential solvation of FLU by the protic solvent leads to a fast decrease of Φ_Δ upon addition of increasing amounts of the latter.     

Stabilité dans le méthanol et propriétés thermodynamiques de transfert des cryptates de certains cations de transition et de métaux lourds

Stability in Methanol and Thermodynamic Transfer Properties of the Cryptates of some Transition Cations and Heavy Metals The nature and stability of the macrocyclic and macrobicyclic complexes of Ag⁺, Cd²⁺, and Pb²⁺ (Mⁿ⁺) with 21, 22, 211, 221 and 222 in anhydrous methanol 0.05M in Et₄N⁺ClO^?₄, at 25° (see Scheme) have been determined by potentiometry and spectrophotometry. Binuclear complexes M₂L²ⁿ⁺ have been observed in all cases, besides the mononuclear MLⁿ⁺ complexes. The macrobicyclic 1:1 complexes MLⁿ⁺ exhibit an important ‘cryptate effect’ with Mⁿ⁺=Ag⁺, Pb²⁺ and Cd²⁺, but not with Cu²⁺ and Zn²⁺; their stability is in all cases maximum with 221. The applicability to our results of the recent extrathermodynamic hypothesis involving MLⁿ⁺ cryptates is examined.     

Nitro- and fluoropolyformals. III. Copolyformals from mixtures of fluoro- and nitro-α,ω-diols

Polyformals of fluoro-, nitramine-, and C-nitrodiols show widely differing properties with respect to glass transition temperature, melting transition, and solubility. Polymers with desirable combinations of these properties, e.g., low T_g, high nitro content, and good solubility in polar solvents, were expected to result from acid-promoted copolycondensation of appropriate mixtures of diols with formaldehyde. A series of such condensations were carried out and the polymers obtained from binary mixtures of fluoro- and nitrodiols, different nitrodiols, and fluoro- or nitrodiols and carboranediols, were characterized by GPC, ¹H-NMR, and DSC analysis.     

Analyse isotopique de mélanges d'éthanols deutériés C2H5-nDnOH

The qualitative and quantitative isotopic analysis of mixtures of nuclear isomers of ethanol C₂H_5–nD_nOH is described. The samples are obtained by reduction reactions and in each of them an isomer is markedly predominant. After a mass spectrometric determination of the amount of isotopic species with the same overall deuteration, these species are identified by proton and deuteron NMR, by combining the spectral schemes of all the isomers which can be assumed until agreement is reached with experimental spectra; isotope effect on δ is taken into account. The importance of the isotopic varieties are then determined by integrating some characteristic lines, with variable accuacy. For each sample, the total intensities of methyl and methylene signals are also compared in proton and deuteron resonance. By elevating the temperature of the sample, one can see the fine structure of a methylene signal broadened by the deuteron quadrupole relaxation.     

Dérivés de sucres à groupement gem-dihalogénoéthényle

Carbohydrate Derivatives Bearing a gem-Dihalogenoethenyl Group Treated with the appropriate Wittig reagent, aldehydosugar derivatives ( 1–13 ) led in good to excellent yields to the expected gem-difluoro, gem-chlorofluoro-and/or gem-dichloroenoses ( 14–29 ). Examples of their dibromo analogues had been previously described (see e.g. [1]) but the diiodo derivatives could not be isolated, The influence of the conditions on the yields is reported as well as spectroscopic properties (particularly the long-range ¹³C, ¹⁹F- and ¹H, ¹⁹F-coupling constants) of these new enoses.     

Acid-catalyzed isomerization of caryophyllene in the presence of SiO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> impregnated with sulfuric acid

The conversion of caryophyllene upon contact with Al₂O₃ and SiO₂ impregnated with sulfuric acid was carried out, and the components of the resulting mixtures were identified. Having in hands such “standard” mixtures greatly facilitates identification of components of sesquiterpene fractions of essential oils and other mixtures of natural origin. The catalytic activity of silica gel impregnated with sulfuric acid (H⁺-SiO₂) in the acid-catalyzed isomerization of caryophyllene is significantly higher than that for H⁺-Al₂O₃ and is comparable with the activity of concentrated sulfuric acid.     

Substitution électrophile aromatique dans l'anhydride sulfureux liquide. Influence de la concentration en bromure et rôle du solvant sur la réactivité des anisoles au cours de la réaction de bromation

Electrophilic Aromatic Substitution in Liquid Sulfur Dioxide. Kinetic Dependance of Rate on the Bromide Concentration and Influence of the Solvent during the Course of the Reaction On the reported data for bromination of anisole and eleven of its derivatives in liquid SO₂, it was shown that, with a large excess of bromide, the rate of reaction, obeys a first-order law. Rate constants thus obtained do not discriminate between the two different forms of bromide, e.g. Br₂ and Br^?₃ present as the A⁺Br^?₃ form, and corrections were made by use of the apparent equilibrium constant K′ for tribromide formation. The variations of rate constants with initial concentration of bromide has been studied and the effect results in a retardation of the bromination rate. Moreover, the ratio [Br₂] [A⁺Br^?]_T, which is constant during an experiment, varies with initial bromide concentrations, this variation affecting the total rate. To account for the bromide effect on the reactivity, variations of k^o,p_g {1 + K′[A⁺Br^?]_T}VS[A⁺Br^?]_T were studied over a 0.01 to 1M range of bromide concentration. The mechanism proposed shows that liquid SO₂ helps the reactive intermediate to be deprotonated and because of solvation of reactive species this step would probably be rate determining. Bromination by molecular bromine is more sensitive to substituent effects in liquid SO₂ than in water. This result is ascribed to the +M effect of the methoxy group which increase the conjugation of ortho-substituted derivatives (p⁺_p = ?7.83; p⁺_o= ?10.47).     

Résonance Magnétique Nucléaire. V.—Etude de Chlorures Vinyliques par RMN 1H. Incréments spécifiques des radicaux alkyle

Twenty five geometrical isomers of vinylic chlorides have been isolated and studied by ¹H n.m.r. and g.l.c; some of these have been chemically reduced for identification. New values of alkyl substituent increments for the estimation of olefinic proton chemical shifts are listed. The effect of chlorine (down field shift) on vinylic allylic and homoallylic protons is described, as well as the solvent effect of benzene (high field shift).     

Une fonction d'onde autocohérente (self-consistent) sans restriction de symétrie pour 1′état X3Π de la molécule BN

We give the self-consistent wave functions for the BN molecule in the …(5 σ) (1 π⁺)² (1 π^?), X³ Π state. These wave functions are obtained as linear combinations of SLATER orbitals of the atoms. In this openshell case the π⁺ and π^? orbitals belonging to the same symmetry species but to different subspecies are allowed to vary independently. Their coefficients are found rather different from one another; this seems to mean that the effect of the usual symmetry restriction could be relatively important in such cases.     

Tétraazamacrocycles lipophiles: Extraction d'ions métalliques par une résine imprégnée

Lipophilic Tetraazamacrocyles: Extraction of Metal Ions by Impregnated Resin Extraction of Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and Ag⁺ by lipophilic tetraazamacrocycles dispersed on a solid matrix (Amberlite XAD7) is reported. Extraction efficiency is sensitive to the metal ion identity and the cavity size of the macrocycle. The influence of kinetic factors upon extraction efficiency is discussed.     

Photochimie d'hétérocycles azotés. IV. Transposition de type photo-fries des N-acétyl benzimidazolones

The photolysis of benzene or alcoholic solutions of N-acetyl-and N,N-diacetylbenzimidazolones gave mixtures of ortho- and para-rearrangements products accompanied to some extent with de-N-acylation. The different products have been identified by means of nmr, mass spectrometry and unambiguous synthesis.     

Etude par spectrométrie de masse de l'ionisation de benzonitriles,de phénylacétonitriles et de N,N-diméthylanilines substitués

Molecular ionization potentials for series of compounds of the type X? C₆H₄? CN, X? C₆H₄CH₂? CN and X? C₆H₄? N(CH₃)₂ have been measured using the retarding potential difference technique (RPD. technique). The effect of the various substituents X is better correlated through the electrophilic Brown σ_p⁺ constants than through Hammett's σ_p values. No meta-para orientation effect is observed. For all the disubstituted phenyl compounds studied, the effect of the second substituent is affected by the electron-releasing power of the original substituent. Ionization potentials calculated by using the semi-empirical method of equivalent orbitals are in good agreement with the experimental values.     

A <Superscript>1</Superscript>H NMR study of Nile Red solvation

In order to evaluate the capabilities of NMR spectroscopy for investigation of the solvatochromic effect in luminophore solutions, the ¹H NMR chemical shifts of Nile Red in mixtures of solvents with different polarities (benzene, toluene, methanol) has been determined. Their dependence upon the solvent mixture composition has been revealed and binding sites for luminophore and solvent component molecules have been determined. The results of the NMR study are consistent with data on the fluorescence of Nile Red solutions in toluene-ethanol mixtures.     

RMN 13C de cyclanones halogénées. Détermination et additivité des incréments du chlore en série cyclohexanique

The ¹³C n.m.r. spectra of fourteen chlorocyclohexanones have been recorded to examine the variation of the ¹³C chemical shifts as a function of the position and the number of the chlorine substituents. Additivity relationships were found which enable reasonable prediction of the chemical shifts of chlorinated cyclohexanones. Comparison between the observed and calculated chemical shifts of mono- and dichlorinated flexible molecules shows that the chlorine effects are additive.     

A field ionization and collisionally activated dissociation/charge stripping study of some [C9H10]+˙ ions

The extent of isomerization of [C₉H₁₀]^+˙ ions, with lifetimes of approximately 10^?11 and 10^?6 s has been investigated using field ionization, collisionally activated dissociation and charge stripping techniques. The [C₉H₁₀]^+˙ ions which were investigated included the molecular ions of α-methylstyrene, β-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, indan, cyclopropylbenzene, allylbenzene and the product of water loss from 3-phenylpropanol. The field ionization spectra of all the C₉H₁₀ hydrocarbons were different indicating that isomerization to a common ion structure had not occurred to a measurable extent for ions with lifetimes of approximately 10^?11 s. Collisionally activated dissociation and charge stripping results indicated that most of the [C₉H₁₀]^+˙ ions continued to maintain unique ion structures (or mixtures of structures) at ion lifetimes of 10^?6 s. Possible exceptions are the [C₉H₁₀]^+˙ ions from allylbenzene and cyclopropylbenzene which gave indistinguishable collisionally activated dissociation and charge stripping spectra.