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.     

Déplacements chimiques induits en RMN par un réactif lanthanidique: I—Application á l'analyse conformationnelle de sulfites cycliques

The chemical shifts induced by Eu(fod)₃ in several series of 6-membered cyclic sulfites give the parameters K_c and Δ_SR of the complexation equilibrium for an assumed 1:1 stoicheiometry. The equilibrium constant K_c decreases with increasing bulk of the C-4 and C-6 substituents and polarity of the C-5 substituent, which corresponds to the increase of the i.r. stretching frequency vS?O. Thus axial S?O will be more tightly complexed than equatorial S?O. It can be predicted that when a conformational equilibrium exists without shift reagent, displacement towards an axial S?O form will occur with the reagent. Use of the Δ_SR pseudocontact equation confirms the following: (i) ax S?O chair forms are stabilized; (ii) eq S?O chairs with two eq C-4 and C-6 substituents show an equilibrium with a few percent of the ax S?O flexible conformation, particularly in the absence of an ax C-5 substituent; (iii) twist forms with a 2–5 axis, intermediate S?O and trans-4, 6-di-tert-Bu substituents give a boat form with O at the prow and ax S?O; (iv) the conformational equilibrium of trans-5-tert-butyl-2-oxo-1, 3, 2-dioxathiane (chair with ax tert-Bu and S?O ? 70%) is completely displaced towards that form; (v) cis-4,4,6-trimethyl-2-oxo-1,3,2-dioxathiane, which exists as an equilibrium in which the three types of S?O occur, is complexed essentially in the twist form with a 1–4 axis and ax S?O. Most of these results are supported by the coupling constants analysis for the ratio R₀/S₀ = 1.     

Etude en Résonance Magnétique Nucléaire et Stéréochimie d'un Composé Cyclopropanique d'Intérět Thérapeutique. Résonance du Proton à 250 MHz avec Triple Irradiation

1-Pivaloyl-2-hydroxymethylcyclopropane is studied with nuclear magnetic resonance. The C-1? C-2 configuration is determined from the 250 MHz n.m.r. spectrum (triple irradiation experiments have been performed for this purpose). Rotational isomerism around the ring-carbonyl bond is studied from the ASIS effect. Rotational isomerism around the ring-hydroxymethyl bond is studied from vicinal coupling constants over a temperature range of ?20 to +125°C. From the J(HOCH) coupling constant (in CCl₄) rotamer populations of the hydroxyl group are examined and the overall conformational distribution can be established.     

Etude en Spectrométrie de Masse. IX—Fragmentation de Cyclopropanes Dicarboxylate de Méthyle-1,2 cis et trans Diversement Substitués,et des Homologues Cyclobutaniques,Cyclopentaniques et Cyclohexaniques non Substitués

A mass spectral study of cis- and trans-decarboxymethylcyclopropanes substituted on C-1, C-2, C-3 reveals that they show the same behaviour under electron impact. In every case, breaking of the carbocyclic ring is the first step giving the most important peaks. By comparing unsubstituted diesters of cyclopropane with those of the cyclobutane, cyclopentane and cyclohexane homologues, we have analysed the transmission of electronic effects by the different rings.     

Hétérocycles contenant du phosphore: XXVIII—Etude par Résonance Magnétique Nucléaire et analyse conformationnelle de quelques oxazaphosphorinanes-1,3,2 (II)

The ¹H n.m.r. spectra of some new 1,3,2-oxazaphosphorinanes are analysed. The stereochemistry and the ring conformation is discussed. The free energy and the torsional angle of the C-4? C-5 and C-5? C-6 fragments are calculated for some of these 1,3,2-oxazaphosphorinanes.     

Utilisation du 13C en Spectrométrie de Masse: Etude de la Fragmentation de Disaccharides

Twenty-nine α,β-(1 → 3) and (1 → 4) or β-(1 → 6) disaccharides, in the glucose series were analysed by electron impact mass spectrometry. In addition to the known mechanism, a few ¹³C labelled compounds led us to suggest that the ion c was formed from the reducing unit B and the C-1′ of the non-reducing residue A, while A was the starting point for rearrangement and fragmentation processes.     

Détermination par RMN 1H et 13C des Couplages J(CH) et J(CC) dans des Monomères Precurseurs de Lignine: Vanilline,Férulate d'Ethyle et Alcool Coniférylique Sélectivement Enrichis en 2H et 13C

Some monomer model compounds of lignin have been selectively ²H and ¹³C labelled: vanillin, ethyl ferulate, coniferyl alcohol and ethyl hydrogen malonate. Deuterium isotope effects on the ¹³C chemical shifts in [formyl-²H]vanillin, [5-²H]vanillin and [α,α,5-²H₃]coniferyl alcohol made the unambiguous assignment of the aromatic ¹³C signals possible. Absolute ^1,2,3J(CC) values have been determined on ¹³C spectra of [formyl-¹³C]vanillin, and of ethyl ferulate and coniferyl alcohol in which the vinylic C-γ and C-β carbons were ¹³C enriched. It has been possible to measure ⁴J(C?O, C-4) in vanillin and ⁴J(C-γ, C-4) in ethyl ferulate. The determination of ^1,2,3,4J (CH) absolute values was done by means of gated decoupled ¹³C spectra of the non-labelled compounds. When second order effects made the use of this technique impossible we determined certain J(CH) values and their signs either by analysing the ¹H NMR spectra of ¹³C labelled coniferyl alcohol [²J(C-β, H-γ), ²J(C-β, H-α), ²J(C-γ, H-β), ³J(C-γ, H-α)] or by a double irradiation experiment on the 250 MHz ¹H NMR spectrum of ethyl [β-¹³C] ferulate [for ²J(C-β, H-γ)].     

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.     

Un nouvel exemple de transposition: l'épimérisation en C(3) d'hydroxy-3-δ1-pyrazolines dérivées de sucres

A Novel Example of Reversible Ring Opening: The Epimerization at C(3) of Sugar 3-Hydroxy-Δ¹-pyrazolines Reaction of 1 (either geometrical isomer) with hydrazine followed by in situ Ag₂O oxidation led to two pairs of interconverting isomers 4 ? 5 and 6 ? 7 . By the same treatment, (Z)- 10 and (or) (E)- 10 gave the pair 11 ? 12 . Acetylation of 4 ? 5 led to a non interconverting mixture of 8 and 9 . This fact, and the lack of incorporation of ¹⁸O when the epimerization took place in the presence of H₂¹⁸O indicated that the most probable mechanism consisted in a reversible ring opening ( D ? E ? F ). The kinetic parameters of these reactions are given and structural assignments proposed for the new compounds.     

Stéréochimie en série aziridine: VI—Etude en Résonance Magnétique Nucléaire d'alcools aziridiniques primaires (configuration à l'azote,isoméries de rotation)

The PMR spectra of six primary aziridinyl carbinols are studied over a temperature range of ?30°C to +100°C. Nitrogen configuration is determined. When the inversion process is effective, kinetic parameters are evaluated. Rotational isomerism about the ‘ring? CH₂OH’ bond is studied from vicinal coupling constants associated with the two diastereotopic protons on the ? CH₂OH group. From the J(HOCH) coupling constant (in CCL₄) rotamer populations of the hydroxyl group are determined in some cases and the overall conformational distribution can be established.     

Etude en Basse Tension de l'Androstane Dione-3,17—Application a la Localisation du Deuterium

The fragmentation mechanisms of (5α) 3,17-androstanedione have been studied in order to determine whether the deuterium is located at C-4 or C-6. This is possible at low voltage where a peak at m/e 216, arising from a A-ring cleavage allows the determination of isotope distribution between C-4 and C-6.     

Sur la Similitude des Déformations du Noyau Cyclohexanonique Induites par les Groupes Tertiobutyle et gem-Diméthyle

X-ray and NMR (250 MHz) data for chlorinated 4,4-dimethylcyclohexanones lead to the following conclusions: carbonyl and chlorine substituent effects on ²J and ³J coupling constants are similar to those observed for 4-tert-butylcyclohexanones. In other respects, the gem dimethyl and the tert-butyl groups induce on the ring similar large ⁴J coupling constants (H-3′? C-3? C-4? C-5? H-5′); the results can be interpreted in terms of local gemoetric deformations and additivity of these deformations. The determination of dihedral angles by Lambert's method and from X-ray data shows the identity of the structures in the solid state and the dissolved state and confirms the great structural similarity between 4-tert-butyl- and 4,4-dimethylcyclohexanone derivatives.     

Recherches en série diazépine-1,4 et triazépine-1,2,4. XV. Syntlièse d'halogéno-3(7)-s-triazolo[4,3-b] triazépinones

Halogenation of s-triazolo[4,3-b]triazepinones gas been accomplished by several methods. According to the agents used it has been possible to halogenate the triazepine ring (C-7 carbon) or (and) the triazole ring (C-3 carbon). Thus eighteen halogeno triazolotriazepines have been synthesized and their structures established from the spectral data.     

Etude Conformationnelle par Résonance Magnétique Nucléaire Protonique des Dérivés de la O-Isopropylidène-2′,3′ Adénosine

Conformational analysis using ¹H n.m.r. data (δ, ³J and NOE) has been carried out on several derivatives of 2′,3′,-O-isopropylideneadenosine bearing various substituents at positions C-5′, C-8 and N-6. Conformational modifications are assigned to specific interactions between the sugar and purine moieties and also to solvent effects.     

Analyse Conformationnelle par RMN du Proton des Oxo-2 Oxathiazannes-1,2,3 (Sulfinamates Cycliques) Diversement Substitués en 3, 4 et 6

In this study, carried out with 16 compounds, the chair form with an axial S?O group (CA) is found, in the absence of C-4, C-5 and C-6 substituents, to be the most stable (ΔG>8,4 kJ mole^?1), as previously reported for analogous cyclic sulfites. When methyl or tert-butyl substituents are present on the 4 and 6 carbon atoms, the conformation of the ring depends on their respective orientation towards the S?O group, and on the nature of the substituent of the nitrogen atom. For the trans isomers, the conformation remains anancomeric chair (CA) except when important gauche interactions exist: thus the strong Me/tBu gauche interaction in the 3-tert-butyl-4-t-methyl-2-r-oxo-1,2,3-oxathiazan induces a twist form with a 3,6-axis and an axial S?O group (CNA). When the 4- or 6-substituent is cis, the conformation of the sulfinamate may be either a chair form with an axial S?O group (CA), if the 4-substituent is a methyl, (even with a tert-butyl group in the 3-position which would be in the axial orientation) or a twist form with a 1,4-axis and an axial S?O group (COA) if the 4-substituent is a tert-butyl. Unlike cyclic sulfites, the equatorial SO chair form (CE) and the twist forms with a 2,3-axis and an isoclinal S?O group (CS, CS′) are rarely involved.     

Résonance Magnétique Nucléaire en phase nématique. Exploration de la barrière d'empêchement à la libre rotation de la monofluoroacétone

The NMR spectra of monochloro-, monobromo- and monofluoroacetone (CH₃? CO? CH₂X with X = Cl, Br, F) oriented in a nematic phase have been measured and the direct dipolar coupling constants determined. The barrier to internal rotation for the CH₂F group has been studied for fluorine compound using various hypotheses. The best agreement with IR data has been obtained using the potential equation V(θ) = Σ_n V_n × (1 – cos nθ)/2 and a Boltzmann distribution of the CH₂F group (V₁ = 250 ± 50 cal.mol^?1, V₂ = 1650 ± 100 cal.mol^?1, V₃ = ?1000 ± 100 cal.mol^?1).     

Constantes de couplage vicinales à travers deux hétéroatomes: III—Calculs théoriques et mesures expérimentales dans les hydrazides enrichies en 15N

Different calculations, among them those utilizing the finite perturbation theory with INDO wave functions, have been effected to calculate the value of the ³J(¹H ? N? N? ¹H ) coupling constant in hydrazides as a function of the dihedral angle. Experimental coupling constants have been compared with calculated ones in order to determine the conformation around the N? N bond. The first example of a ²J(¹H ? N? ¹⁵N ) coupling is described.     

Etude structurale de la bipyrimidine par RMN en phase nématique

The 240 MHz NMR spectra of bipyrimidine in the nematic phase of p-methoxybenzylidene-p-n-butylaniline is analysed. The para H,H inter-ring distance is determined. The barrier to internal rotation of the inter-ring C? C bond is studied. Excellent agreement between experimental and calculated spectra is obtained using potential function V(?) = ½ Σ_NV_n (1 – cosn ?) with V₁ = V₂ = V₃ = 0 cal mol^?1 and V₄ = 500 cal mol^?1.     

Dérivés Alléniques du Phosphore. Influence de l'État de Coordination du Phosphore et de la Nature des Radicaux Liés au Phosphore sur les Signes de J(P?H)

The signs of the phosphorus-proton coupling constants in various allenic organophosphorus compounds have been determined by either analysis of the AB₂X spectra or double resonance. Probable absolute signs have been obtained by taking ³J(P? H) as positive. In allenic phosphine oxides, the following signs are obtained: ²J(P? H) +ve, ³J(P? H) +ve, ⁴J(P? H) ?ve, ⁵J(P? H) +ve and the ⁴J(P? H) coupling constant varies mostly with the inductive effect of the substituents bound to the phosphorus atom. In allenic phosphines, these sings are: ²J(P? H) +ve, ³J(P? H) +ve, ⁴J(P? H) ?ve and +ve and the ⁴J(P? H) coupling constant varies with both the inductive and resonance effects to the substituents. This coupling constant is negative except when the phosphorus atom is bound to groups which are electron-donating by resonance effects. These results are discussed in relation to the pπ? dπ bonding in phosphine.     

Analyse Conformationnelle de Pseudoprotoberbérines Naturelles. II. Etude Structurale par RMN de 13C des Tétrahydropseudoprotoberbérines provenant de I'Isopyrum thalictroïdes

The four pseudoprotoberberins extracted from Isopyrum thalictroides L. were reduced with sodium borohydride to the corresponding tetrahydropseudoprotoberberins. Comparison between the ¹³C NMR spectra of these and of synthetic protoberberins allowed us to assign a trans-1 configuration to the four reduced alkaloids and also to provide for this particular configuration an unequivocal criterion for the differentiation (based on the chemical shift of C-8) between tetrahydroprotoberberins (9, 10 substituted) and tetrahydropseudoprotoberberins (10, 11 substituted).