Spectres de masse des composés organiques. 5e communication. Perte de méthane et d'éthylène à partir des ions butyle

The loss of methane and ethylene in the mass-spectrometric fragmentation of different isomeric butyl ions which originate from butyl halides has been studied. The different carbon atoms in n-butyl are already equivalent after 10^?7 s, whereas the statistical distribution of the hydrogen atoms within the molecule can only be observed for the metastable peaks. A protonated cyclobutane structure is proposed as an intermediate product in the fragmentation of the n-butyl ion. The fragmentation of this model has been simulated by a computer. This allows prediction as to the time-scale of fragmentation. The comparison of this model fragmentation with that of isomeric butyl ions shows that, even in the decay of the tertiary butyl ion, the formation of the proposed rearranged cyclic structure competes favorably with the direct fragmentation.     

Spectrométrie de Masse de Benzylidène—Acétals d'Hexopyranosides

The electron impact fragmentation is reported for 46 benzylidene acetals of hexopyranosides of the allo, altro, galacto, gluco, gulo and manno series and some of their mono-oxidation products. Besides the molecular ion, which is always present and is usually part of a triplet the previously reported ion formed by cleavage of C-1? C-2, C-4? C-5 and the benzylic C? O(C-4) bond is observed. Evidence is given for two complementary ruptures (C-1? C-2, C-3? C-4; C-1? O-5, C-2? C-3, fragmentations whose intensities depend on the substituents or functional groups present in the molecule. In most cases these fragmentations allow an assignment of the substitution mode of these 1,3,6-trioxa-bicyclo-[4.4.0]decane systems. The limitations of this method are discussed.     

Effets Isotopiques dans la Fragmentation par Impact Électronique de Méthanols Deutériés

The mass spectra of the CH₃OH, CH₂DOH, CD₃OH, CH₃OD and CD₃OD methanols have been recorded at nominal electron energies ranging from 11 to 35 eV. Curves are given for the variation of the isotope effects related to the molecular ion stability and bond cleavage probabilities as a function of the electron energy, and are compared with a priori calculations. A simple distribution function and a value for the number of oscillators equal to half the theoretical figure give fairly satisfactory agreement, except as concerns the molecular ion stability. The form of the curves for the latter could be explained by the existence of an electronic state of the molecular ion other than the ground state.     

Recherches dans la série des cyclitols XXXVII Etude par spectrométrie de masse

Low resolution mass spectra of cyclohexane-triols, -tetrols, -pentols and -hexols and of some of their deuterium labelled derivatives have been measured. The results indicate that for some geometrical isomers quantitative differences between ion intensities are significant, allowing to deduce the stereochemistry of the molecule from its mass spectrum. In all these compounds the electron impact induced elimination of water occurs mainly by interaction between OH groups. There is a correlation between the relative abundance of (M – H₂O)⁺ and (M ?2 H₂O)⁺ ions and the number of axial hydroxyls in the more stable conformation of the molecule. Difficulties encountered in deducing fragmentation patterns, and determination of number and position of deuterium atoms in the molecule of ms-inositol are discussed.     

Fragmentation de la Méthyl-2 Indolizine sous Impact Electronique: perte de H˙ à partir de l'Ion Moléculaire; perte de HCN à partir de l'Ion [M?H˙]+

The origin of the hydrogen radical lost in the ionization chamber from the molecular ion of 2-methylindolizine has been studdied by examination of the spectra of four specifically deuterated species. Hydrogen loss involves preferentially a hydrogen from the methyl substituent but also one of the hydrogens of either ring, especially those of the 5-membered ring. The HCN elimination from the metastable [M? H^˙]⁺ ions was studied using a linked scan method; the results are consistent with loss of identity of all the hydrogen atoms of the precursor ion, which implies an extensive reorganization prior to fragmentation.     

Analyse des spectres de vibration infrarouge et Raman de benzothiazolines et de 2H-chromènes, éléments constitutifs de spiropyrannes benzothiazoliniques. Aspect synthétique

Study of infrared and Raman spectra of benzothiazolines and 2H-chromenes, constitutive parts of benzothiazolinic spiropyrans. Synthetic aspect. We have synthesized some benzothiazolines and some substituted 2 H-chromenes as models of the two halves of benzothiazolinic spiropyrans with the aim of interpretation of infrared and Raman spectra of spiropyranic structure. While doing that, we have been able to improve the synthesis method of chromenes obtained from coumarins and we have prepared new nitro-chromenes. By studying IR. and Raman spectra of the two halves of spiropyranic molecule, we could propose a rather good attribution of fondamental modes of vibration. This attribution will used as base for the interpretation of IR. and Raman spectra of a series a benzothiazolinic spiropyrans.     

Alcoylation d'acridanone-9. Premiers exemples de O-alcoylation dans cette série de composés

The results of nucleophilic substitution of the 2-methoxy-9-acridone are discussed in terms of competition between both ionic sites N^? and O^?, of the molecule. They are the first examples of O-alkylation of substituted 9-acridone.     

Chimie et pharmacologie de l'apiose III. Synthèse et propriétés de l'hydrate de l'O-isopropylidène-1, 2-tétrosulo-3-furannose

Ruthenium tetroxide oxidation of 1, 2-O-isopropylidene-β-D -threofuranose affords, besides the known 1, 2-O-isopropylidene-α-L -glycero-tetros-3-ulofuranose, a lactone. The tetrosulose is easily hydrated to the corresponding gem-diol whose dehydration on molecular sieves leads to a branched-chain dimer. Lead tetraacetate oxidation of 1, 2-O-isopropylidene-α-L -glycero-tetros-3-ulofuranose p-nitrophenylhydrazone leads quantitatively, to a gem-azoacetate, a new synthetic intermediate in carbohydrate chemistry. The 3-O-acetyl-1, 2-O-isopropylidene-α-L -glycero-tetr-3-enofuranose is easily obtained from the gem-diol. A highly stereoselective procedure is described to prepare the 3-O-acetyl-1, 2-O-isopropylidene-α-L -3, 4-exo-D₂-erythrofuranose.     

Etude par spectrométrie de masse du cyclopentanediol-trans-1,2

The electron impact induced fragmentation of trans cyclopentane-1, 2-diol has been investigated using derivatives specifically labelled with deuterium and high-resolution mass spectral data. The elimination of the elements of water from the molecular ion involves at least three mechanisms whose relative importance has been evaluated. A fragmentation scheme based upon metastable peaks and labelling is presented.     

Sur le mécanisme de la réaction de meth-cohn-tarnowski de préparation des thiocoumarines

Reaction of 2-t-butylthiobenzaldehyde with N-(2-dialkylaminoethyl)-cyanacetamides followed by heating of the resulting 3-(2-t-butylthiophenyl)-2-cyanoacrylamides in polyphosphoric acid leads to the formation of 3-carboxamido-2-imino-2H-benzo[b][l]thiopyrann intermediates which afford thiocoumarins on hydrolysis. The authors postulate the intermediate formation of a thiophenate ion by an electronic mechanism involving six centers.     

The [CH2CHOH.+, CH3CHO] solvated enol radical cation

The bimolecular reaction of the CH₂CHOH^.+ enol ion (m/z 44) with acetaldehyde gives a strongly dominant product,m/z 45, formed mainly by proton transfer from the ion to the molecule. The abundance of the product coming from a H^. abstraction reaction from the neutral, albeit more exothermic, is negligible. In order to explain this result, the long lived [CH₂CHOH^.+, CH₃CHO] solvated ion was generated by reaction of the CH₂CHOH^.+ enol ion with (CH₃CHO) _n in the cell of a Fourier transform ion cyclotron resonance mass spectrometer. The structure of this solvated ion was clearly established. Labeling indicates that [CH₂CHOH^.+, CH₃CHO], upon low energy collisions, reacts by H^. abstraction more rapidly than by H⁺ transfer to the neutral moiety. This shows that the entropic factors are determinant when the enol ion reacts directly with acetaldehyde.     

Tautomerism and proton transfer in photoionized acetaldehyde and acetaldehyde–water clusters

Understanding the gas‐phase chemistry of acetaldehyde can be challenging because the molecule can assume several tautomeric forms, namely keto, enol and carbene. The two last forms are the most stable ionic forms. Here, insight into the gas‐phase cluster ion chemistry of homogeneous acetaldehyde and mixed water–acetaldehyde clusters is provided by mass spectrometry/vacuum ultraviolet photoionization combined with density functional theory calculations. (AA)_nH⁺ clusters (AA = acetaldehyde) and mixed (AA)_nH₃O⁺ clusters were detected using tunable vacuum ultraviolet photoionization. Barrierless proton transfers were observed during the geometry optimization of the most stable dimer structures and helped to explain the cluster ion chemistry induced by photoionization, namely the formation of deprotonated tautomers and protonated keto tautomers. Water was found to catalyze the keto–enol and keto–carbene isomerizations and facilitate the proton transfer from the ionized enol or carbene part of the cluster to the neutral keto part, resulting in protonated keto structures. The production of protonated keto structures was identified to be the main fragmentation channel following ionization of the homogeneous acetaldehyde cluster and a channel for ionized mixed clusters as well. These findings are significant for a broad range of fields, including current atmospheric models, because acetaldehyde is one of the most prominent organic species in the troposphere and ions play a crucial role in aerosol formation. Copyright © 2014 John Wiley & Sons, Ltd.     

Etude de la fragmentation par impact électronique en ions positifs et négatifs de dérivés nitrés de l'amino-2-benzothiazole

Study of Positive and Negative Ions Electron Impact Fragmentation of 2-Amino-benzothiazole Nitro Derivatives The positive and negative ions mass spectra of 2-amino-4,6-dinitrobenzothiazole ( 1 ), 2-amino-4-nitrobenzothiazole ( 2 ), 2-amino-6-nitrobenzothiazole ( 3 ) are reported and discussed. These compounds give an intense molecular ion and show interesting fragmentations in both positive and negative ions spectra. Specific ¹⁵N-labelling was used in order to confirm the fragmentation patterns.     

Mécanisme de solvolyse des cis- et trans-(p-toluènesulfonates) d'aryl-2-cyclopentyle I. Etude de la première étape de la solvolyse: effets isotopiques de l' atone de deutérium en position 2, effets de sel basique et effet spécial de sel

Solvolysis Mechanism of cis - and trans-2-Arylcylopentyl p-Toluenesulfonates. The Step: 1-Deuterium Isotope Effects, Basic Salt Effects, and Special Salt Effect We have studied the first step of the solvolysis of cis and trans-2-arylcyclopentyl p-toluenesulfonates in HCOOH, AcOH, and EtOh. All substrates show a high kinetic 1-deuterium isotope effect (k_H/k_D(1) >1.15). This fact indicates that first step leads to classical intimate ion-pair Which dissociates to a solvet-separated ion-pair, without participation either of solvent, the 2-aryl group, or a H-atom at C(2). The slight influence of added basic ions on reaction rate allows us to exclude any direct solvent attack on the covalent substrate even in the most favorable case, i.e. ethanolysis of 2-(p-nitrophenyl)cylopentyl-p-toluenesulfonates. Furthermore, solvent-separated ion pair formation is indicated by the special salt effect induced by LiClO₄.     

Nouvelle méthode de préparation d'éthers vinyliques à partir d'acétals

A new way to vinylic ethers from acetals Acetals react at low temperatures in presence of a Lewis acid (aluminium chloride or magnesium bromide) with tertiary amine to give in good yields the vinylic ethers corresponding to the elimination of one molecule of alcohol.     

Étude des Paramètres de Résonance Magnétique Nucléaire et de la Stéréochimie de Thiono-2 R-2 Dithiaphosphorinanes-1,3,2

The ¹H, ¹³C and ³¹P n.m.r. spectra of eleven 2-R-2-thiono-1,3,2-dithiaphosphorinanes with various R groups attached to the phosphorus atom have been recorded and analysed. In the compounds where R=Cl, OMe or N, the molecule adopts a chair conformation with the R group axially oriented. When the molecule adopts a chair conformation with equatorially oriented R. In the case of the derivatives with R=phenyl, Me, N(Me)₂ or NHt-Bu, a chair–chair conformational equilibrium was observed. The hindered rotation about the P? N bond was also examined in the derivative with      

Analogie Photochimique. II—Cyclisation des Aldéhydes δ,ε Insaturés sous Impact Electronique

The mass spectra of 4, 4-dimethyl δε-unsaturated aldehydes show an ion at m/e 126 which results from the elimination of a neutral olefin directly from the molecular ion. This fragmentation is shown to occur through a cyclohexanone intermediate involving a process whcih has its equivalent in the photochemistry of these aldehydes. The abundance ratios of the unimolecular metastable decompositions of these m/e 126 ions are in excellent agreement with the proposed mechanism.     

Utlisation d'ylides du phosphore en chimie des sucres. XIII. Synthèse de dérivés des hydroxyméthyl-3-D-glucose et-D-galactose et de composés voisins

The treatment of the 1, 2:5, 6-di-O-isopropylidene-α-D -ribo- and xylo-hexofuranos-3-uloses with cyanomethylenetriphenylphosphorane led in each case, and in almost quantitative yields, to a pair of geometrical isomers of C-cyanomethylenic sugars having respectively the ribo and the xylo configurations. Permanganate oxidation of these branched-chain unsaturated sugars afforded the corresponding gem-hydroxyformyl compounds bearing the formyl group on the more hindered face of the molecule. The formyl group of these sugars is easily derivatized to an oximino or reduced to a hydroxymethyl. The configuration at the new asymmetric carbon has been established by comparison with known compounds or by synthesis of a C(3) epimer by the classical route involving a Grignard reagent.     

Ionisation Chimique de Composés Aromatiques Nitrés

The collision induced dissociations of [MH – 30]⁺ ions observed in the chemical ionization (methane) mass spectra of some nitro aromatic compounds show that these ions are formed by reduction in the ion source with subsequent protonation and not by the previously reported losses of NO^· from the protonated molecular ions.