Transferts Protoniques de Sels d'Ammonium Substitues—VIII: Sels de Pyridinium 4-Substitues

The deprotonation rate 1/τ of the title compounds, [4 – R – Py H]⁺, where R = NH₂, t-Bu, Me, Cl, Br or CN, is measured using the coalescence of the pyridinic α-protons, in a mixture CF₃COOH/H₂O/HClO₄ of variable acidity Ho, at 38°C. 1/τ is a linear function k/ho of the acidity 1/ho. k is approximately proportional to the water content and independent of the salt concentration, which seems to be evidence for an exchange with an intermediate pyridine hydrate, according to: . After a preliminary ionisation step: k values, like K_A, fit a Hammett relationship (ρ = 5,05), except for R ? NH₂, and are very sensitive to the nature of R (k = 3,44 × 10² for R = NH₂ and k = 3,14 × 10⁸ M^?1 s^?1 for R ? CN), while k_H values (10¹⁰ s^?1) are not.     

Transferts Protoniques de Sels D'ammonium. Substitues—II: Vitesse D'inversion a L'azote Par la Methode de ‘Protonation Competitive’

Nitrogen in version rate of an amine may be brought to within the NMR time-scale by use of an acidic medium of variable pH, in which it is almost completely prevented through protonation. Rigorous equations are derived for computing this rate from the mean lifetime of the ammonium cation determined by NMR spectroscopy. The validity of Saunders and Yamada's approximate formula is discussed: the protonation rate of the amine must be far larger than its nitrogen inversion rate, while the rate at which the salt loses its acidic proton is immaterial. If in version occurs between two different isomers, the equilibrium ratio of the isomeric cations is also derived.     

Le Spectre de L'Alcool Propargylique en Fonction du pH. Un Exemple de Transferts Protoniques Complexes sur un Diacide Organique

Dimethyl sulphoxide (DMSO) is used as a solvent to investigate the kinetic acidity of very weak organic diacids by ¹H d.n.m.r. An inspection of the spectrum of propargyl alcohol as a function of the pH allows the assignment of various proton transfer mechanisms:      

Etude de la Réaction d'Hydrolyse de l'Anion PO3F2− en Solution Aqueuse

Investigation of the Hydrolysis of the PO₃F^2? Anion in Aqueous Solution Hydrolysis of monofluorophosphate solutions has been studied by ionic chromatography. We have shown that pH is the leading factor. The rate constant is indeed fourty times more important at pH 2, compared to pH 4, independent on the temperature. Hydrolysis is only little dependent on the cation involved in the solution and on the acid added to reach the desired pH. The activation energy determined for this first order hydrolysis reaction is 24 kcal/mole.     

Etude de la Volatilisation de Quelques Sels de Sodium en Spectro-photometrie d'Absorption Atomique Sans Flamme

Abstract

The non-atomic absorption signals obtained from 9 sodium salts from a graphite atomizer are examined. The influence of nitric, sulfuric and phosphoric acids on NaCl matrix as well as the influence of Ca, Ba, Sr, Mg and Pt salts on Na₂SO₄ matrix are studied. The elimination of NaCl and Na₂SO₄ matrix has been obtained.

En spectrophotométrie d'absorption atomique sans flamme la présence d'une matrice se traduit dans de nombreux cas lors de l'atomisation d'un élément par l'existence d'une absorption non spécifique qu'il convient de différencier avec exactitude de l'absorption spécifique. Différents procédés ont été développés (arc deutérium, effect Zeeman.) permettant de réaliser une correction avec une justesse en règle générale d'autant meilleure que les variations d'amplitude sont moins rapides. Dans la pratique, il èest très rare que le mode opératoire utilisé ne se traduise pas par de faibles surcorrections ou mème sous-corrections perturbant gravement l'exactitude d'un dosage au voisinage des limites de sensibilité de la méthode, ce quel que soit le mode de correction employé.

Parallèlement, la présence d'une matrice peut induire des phénomènes physico-chimiques provoquant des interférences génératrices de variations de sensibilité et de sources d'erreurs conséquentes, lors de l'emploi d'une méthode d'addition standard par exemple, notamment au voisinage des limites de détection.

Il est donc toujours préférable d'éliminer la matrice dès lors que cela peut être effectué sans perte du métal [Agrave] doser.

Si cette élimination n'est pas possible, il est intéressant d'étudier la substitution de la matrice initiale par une autre matrice permettant de réaliser le dosage dans des conditions plus favorables.

La connaissance des spectres et massifs d'absorption liés [Agrave] la volatilisation des différentes matrices, et de leurs variations par addition de modifieurs permet dans certains cas d'accéder [Agrave] des substitutions intéressantes notamment pour deux matrices sodées: NaCl et Na₂SO₄.     

Etude en Serie as-Triazine. XIX—Fragmentations Principales de s-Triazolo-as-Triazinones en Spectrometrie de Masse

The mass spectra of s-triazolo[4,3-b]-, -[3,4-c]- and -[3,2-c]as-triazine-7-ones and their N-methyl derivatives are described. The elucidation of fragmentation pathways is made easy by observation of the changes in m/e values on changing position of the methyl substitution. In all cases a triazine ring fragmentation with initial loss of CO, RCN or RCNCO was observed. This result is characteristic of the different isomeric structures of triazolotriazine-7-ones. The comparison of the spectra of these compounds with those of their N-methyl derivatives shows the occurence of a tautomeric equilibrium, as found from u.v. spectroscopy.     

Etude en RMN de l'Association des Sels de Lanthanides avec des Phénols; Application à la Détermination de Structure de Polyphénols Naturels

Interaction of lanthanide salts with phenols in DMSO solution was investigated as a tool for ¹H NMR structure determination in the field of naturally-occurring polyphenolic compounds. Intermolecular competition experiments evidenced reactivity differences with respect to the nature and position of substituents. Empirical rules of reactivity are suggested from which variations observed in the PMR chemical shifts on addition of lanthanide salts to natural polyphenols (flavones, xanthones) were rationalized.     

Sels d'atdp—20 : Relations reactivite-structure dans les cinetiques de decomposition de sels d'atdp substitues. hypersensibilite a des substituants en position 3 de la

The kinetics of decomposition of various propyloxy phosphonium chlorides, the chain of which is substituted with non polar groups in position 2 and polar groups in position 3, have been measured in pyridine and in DMF. The validity of Taft correlation with σ^* parameters have been ascertained within each of the three linear, branched and neopentylic series, using Exner's criterion. In both solvents, it appeared that the sensitivity parameter ?^* for the neopentylic series varies considerably with the temperature and may reach unusually high values. This phenomenon is interpreted by a proximity effect between the substituent and the seat of the reaction, due to steric constraints.     

Sels d'atdp—19: Cinetique de decomposition d'un chlorure d'atdp en chlorure d'alkyle et HMPT. Effet de solvant et effet de sel

The kinetics of decomposition of the 2-methyl-1-pentyloxy(trisdimethylamino)phosphonium chloride, was measured in several solvents. The experimental kinetic order towards the chloride anion was in the range from 2, in a dissociating solvent, to 1 in non dissociating solvents. Hence we afford experimental confirmation of an earlier prevision in the literature. A linear correlation of log k with the dielectric constants of the solvents was found in the case of the systems exhibiting first order kinetics, contrasting with the classical correlation in $\text{1}\text{?}$, generally observed for the reactions between ions of opposite charge. The salt effect has been measured and interpreted. It allows the performance of kinetic runs for non hindered, very labile ATDP salts, by their replacement by a mixture of an ATDP perchlorate and an aryloxyphosphonium chloride, both of which are stable.     

Sels de Pyrylium. XVIII. Etude par RMN du Carbone-13 de Sels d'Aminopyrylium et des Barrières de Rotation dans quelques Cations N,N-Diméthylaminopyrylium

The C-2—N bond of 2-N,N-dimethylaminopyrylium cations has a partial π character due to the conjugation of the nitrogen lone-pair with the ring. The values of ΔG^≠, ΔH^≠, ΔS^≠ parameters related to the corresponding hindered rotation have been determined by ¹³C NMR total bandshape analysis. This conjugation decreases the electrophilic character of carbon C-4 so that the displacement of the alkoxy group is no longer possible. Such a hindered rotation also exists in 4-N,N-dimethylaminopyrylium cations and the corresponding ΔG^≠ parameters have been evaluated. Comparison of these two cationic species shows that hindered rotation around the C—N bond is larger in position 4 than in position 2. Furthermore, the barrier to internal rotation around the C-2? N bond decreases with increasing electron donating power of the substituent at position 4. ΔG^≠ values decreases from 19.1 kcal mol^?1 (79.9 kJ mol^?1) to 12.6 kcal mol^?1 (52.7 kJ mol^?1) according to the following sequence for the R-4 substituents: -C₆H₅, -CH₃, -OCH₃, -N(CH₃)₂.     

Transposition de Cycles Satures en Spectrometrie de Masse III—Etude des Spectres en Basse Tension des Cyclanones

The fragmentation mechanism of cyclanones (cycloheptanone, cyclooctanone and some methylated or deuterated derivatives) was reinvestigated. All the peaks observed can be interpreted on the basis of a rearrangement of the molecular ion. This rearrangement is particularly important at low voltage.     

Etude en Spectrometrie de Masse: VI—Evaluation de l'Induction de la Fragmentation dans les amines β Fonctionnelles

Mass spectra of 22 β-function amines are compared with those of corresponding non-substited amines. Spectral analysis shows that fragmentation is not induceed by the lone-nitrogen atom: keto, ester, amide or nitrile groups also induce this fragmentation and the ratio was evaluated. This very elementary approach, supported by the kinetics of unimolecular reaction is in good agreement with results based on ionisation potential measurements.     

Phosphates d'enols. XII—Etude en Spectrometrie de Masse de Derives Diethyliques et di-n-Butyliques

The mass spectrometric fragmentations of diethyl phosphates (1) and di-n-butyl phosphates (2) are influenced by the nature of the substituents R, R′ and R″ fixed on the double bond When R = H, the loss of ethylene or 1-butene is mainly observed. When R = CH₃, the double rearrangement process occurs with alkyl group participation of the enolic chain.     

Sels d'alkyloxyphosphonium—XVI: Activation de l'hydroxyle anomere des 2,3,4,6 tetra-o-acyl-d-mannopyranoses

The joint action of tris(dimethylamino)phosphine-carbon tetrachloride on a tetra-O-acyl-2,3,4,6-d-mannopyranose leads to one α anomeric oxyphosphonium chloride (ATDP salt). This salt is not isolable, but decomposes to yield an anomeric mixture of 1-chloro derivatives. The reaction with alcohols give rise to the formation of orthoesters while thiophenol reacts to yield only the β-thiomannoside. These results are discussed and interpreted.     

Sels de cobalticinium : II. Proprietes spectroscopiques et polarographiques de quelques derives du cobalticinium

The spectroscopic and polarographic behaviour of some cobalticinium derivatives have been studied. Due to their positive charge these compounds exhibit particular characteristics in comparison with ferrocene derivatives. They give two successive cathodic waves on a dropping mercury electrode. The first corresponds to the formation of cobaltocene whereas the second represents the reduction of the latter compound to give cobaltocene anion.     

Organomagnesien reactif reducteur : VII. Mise en evidence de l'influence des interactions donneur—accepteur au cours de la reduction de benzylidenemalononitriles

The reduction of benzylidenemalononitriles by chiral aromatic organomagnesium halides and the same kind of reduction where there is no or one phenyl group gives opposite stereochemistry. These results suggest the existence of a donor—acceptor interaction between the phenyl groups in one of the transition states.     

Stereochimie en Serie Aziridine—III Etude de l'Isomérie de Rotation d'un Aldéhyde Aziridinique

From the ASIS effect on chemical shifts and from solvent and temperature dependence of the vicinal spin-spin coupling constant of 1-tertiobutyl 2-formyl aziridine, the following conclusion is reached: the less polar rotamer is the s-trans rotamer, which is of lower energy than the s-cis rotamer.     

Sels de cobalticinium: I. Synthese des derives homo- et hetero-disubstitues

Unlike ferrocene, cobalticinium cation is chemically inactive towards electrophilic substitutions and for this reason the number of derivatives in this series is limited. Substituted cobalticinium salts are usually prepared indirectly from substituted cyclopentadienyl derivatives. These intermediates can be obtained by treating substituted cyclopentadienes with strong bases or by reducing fulvenes. Various homo- and hereto-substituted cobalticinium salts have been prepared using this type of reaction. Due to the remarkable stability of the metallocenic skeleton of cobalticinium ion, we have succeeded in obtaining new derivatives transforming ring-substituted cobalticinium salts by known reactions.     

Ionisation et fragmentation en spectrometrie de masse—I: Sur la répartition de la charge positive entre fragments provenant de mêmes ruptures

When a fragmentation takes place in mass spectrometry, the positive charge remains on the fragement with the lowest ionization potential. This criterion, which has been indicated previously for the alkane series is shown to be generally true.     

Recherches en Serie Azabenzodiazepine. III—Fragmentation en Spectrometrie de Masse de Quelques Pyrido,Pyrimido, Pyrazolodiazepinones,Triazino et Triazolotriazepinones

The mass spectra of several pyrido [2,3-b] and [3,4-b], pyrimido [4,5-b], pyrazolo [3,4-b] diazepinones-1,4 and as-triazino [4,3-b], s-triazolo [4,3-b]triazepinones-1,2,4 are reported and analysed. Five different fragmentation pathways of the molecular ion are generally observed, but the main one is an initial loss of CH₂CO which gives rise to 2-methylazabenzimidazole or 2-methyl azabenzotriazole ions. The behaviour of triazolotriazepines which have two further fragmentation pathways is described.