bluuebunny/crossref_metadata_2025_split huggingface dataset:
New tables of ‘ring current’ shielding in proton magnetic resonance
Authors: Haigh C. W. , Mallion R. B. 
Published: May 2005

AbstractA new theory6 for ‘ring current’ effects on the chemical shifts of protons in or out of the plane of a benzene ring is summarized, and pictorially compared with the predictions of the earlier semi‐classical theory of Johnson and Bovey.1 In the Appendix are presented extensive numerical tables of the predicted shieldings.
NMR studies of viomycin
Authors: Viglino P. , Franconi C. , Lai A. , Brosio E. , Conti F. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of antibiotic Viomycin sulphate and its constituent aminoacids in H2O and D2O were examined in a wide range of pH values. The spectra were analysed by proton spin‐spin decoupling experiments and measurements of the relative intensities of the resonance and chemical shift values. Exchange experiments were also carried out and an almost complete assignment of the resonances of the spectra was possible. The data obtained are discussed in terms of possible structures for Viomycin and the presence of intramolecular hydrogen bonds. Some information about the conformation of the molecule is also given. A tentative assignment of the 13C spectrum of Viomycin is given and the experimental 13C chemical shift values compare well with the theoretical ones evaluated by Grant's rule.
The proton chemical shifts of polychlorinated biphenyls
Authors: Welti D. , Sissons D. 
Published: May 2005

AbstractA 220 MHz NMR spectrometer has been used to identify the structure of polychlorinated biphenyls (PCBs). The proton chemical shifts and approximate coupling constants of PCBs fractionated from Aroclor 1254 are given in the text. The spectra of model compounds are included in the supplement. The chemical shifts are also tabulated according to the ring substitution pattern, when it can be seen that the shifts change systematically with the degree of both the total ring substitution and the substitution in the positions ‘ortho’ to the bridging bond between the rings.
A PMR investigation of organic cations—II: Mixed p‐tolyl‐thienyl carbonium ions
Authors: Lazzeretti P. , Schenetti L. , Taddei F. , Spagnolo P. , Tiecco M. 
Published: May 2005

AbstractThe PMR spectra of isomeric p‐tolyl‐thienyl carbonium ions and the corresponding carbinols were studied in order to compare the relative abilities of 2‐thienyl, 3‐thienyl and p‐tolyl groups to stabilize a carbonium ion. The low field shifts in the ions relative to the neutral molecules are discussed in terms of positive charge delocalisation, as seen by a comparison with calculated π charge densities. Additionally, vicinal coupling constants fit a correlation with π bond order, but this applies only to the thienyl groups in the ionic species.
The NMR spectra and conformations of dihydropyran derivatives—II: The conformational energies of carbomethoxy, hydroxymethyl and acetoxymethyl groups at c‐6 of the 5,6‐dihydro‐α‐pyran ring
Authors: Achmatowicz O. , Chmielewski M. , Jurczak J. , Kozerski L. , Zamojski A. 
Published: May 2005

AbstractThe sum of coupling constants of proton H‐6 for conformations H1 and 1H of the 6‐substituted 5,6‐dihydro‐α‐pyran derivatives have been determined with the aid of appropriate, conformationally biased compounds. With the use of these values and the PMR spectra of the title compounds, thermodynamic values of their conformational equilibria and the conformational preferences of the carbomethoxy, hydroxymethyl and acetoxymethyl groups, have been evaluated.
1H and 13C NMR spectra of benzyl compounds
Authors: Zetta L. , Gatti G. 
Published: May 2005

AbstractProton and carbon‐13 spectra of benzyl compounds of the general formula (C6H5CH2)nX with a large variety of X substituents have been measured. While a linear relationship between the CH2 chemical shift and the substituent electronegativity was found both for 1H and 13C, large deviations from linearity were observed for transition metals such as titanium and zirconium. These later results are correlated with the X‐ray studies of the latter compounds.
Transferts Protoniques de Sels d'Ammonium Substitues—VIII: Sels de Pyridinium 4‐Substitues
Authors: Delpuech Jean‐Jacques , Serratrice Guy 
Published: May 2005

AbstractLa vitiesse de déprotonation 1/τ de sels de pyridinium [4 – R –PyH]+, où R  NH2, t‐Bu, Me, Cl, Br or CN, est mesurée par la coalescence du spectre RMN des protons α‐pyridiniques dans un mélange CF3COOH/H2O/HCLO4, d'acidité variable Ho, à 38°C. 1/τ est une fonction linéaire kho de l'acidité 1/ho. La constante k est approximativement proportionnelle à la teneur en eau, et indépendante de la concentration en sel, ce qui semble prouver un échange sur un hydrate de pyridine intermédiaire, selon:
equation image
.Après une étape d'ionisation très rapide:
equation image
La constante k vérifie, comme KA, une corrélation de Hammett (ρ = 5,05), à l'exception de la 4‐aminopyridine. Elle varie done grandement avec la nature de R (de 3,44 × 102 à 3,14 × 102 M−1 s−1 pour R  NH2 et CN), trandis que kH (de l'ordre de 1010 s−1) y est peu sensible.
A study of the 220 MHz proton resonance spectra for a series of biologically important acridine‐type heterocycles
Authors: Angerman Neil S. , Danyluk Steven S. 
Published: May 2005

AbstractThe high resolution proton magnetic resonance spectra of acridine, phenazine, phenoxazine and phenothiazine have been measured at 220 MHz in various solvents and at several temperatures. Spectra for all four molecules were analyzed iteratively and good agreement was obtained between observed and calculated spectra.Significant differences are noted between the coupling constants and chemical shifts of acridine and phenazine on the one hand and phenoxazine and phenothiazine on the other. These differences are attributed to a nonplanar heterocyclic ring conformation for phenoxazine and phenothiazine in solution. Moreover, it is concluded from the temperature measurements that the heterocyclic rings of phenoxazine and phenothiazine are conformationally flexible in the range covered. Possible mechanisms are suggested for the chemical shift and coupling constant changes.
C‐13 magnetic resonance studies of some papaveraceae alkaloids
Authors: Nakashima Thomas T. , Maciel Gary E. 
Published: May 2005

AbstractThe natural abundance 13C magnetic resonance spectra of some Papaveraceae alkaloids have been determined at 22·628 MHz employing the pulse Fourier transform technique. Several techniques were employed to aid in spectral assignments and it has been possible to make self‐consistent assignments for all the resonances for these alkaloids. Evidence is presented for trans‐annular interaction between the amino group and the carbonyl group situated across the ten‐membered ring.
Proton and boron‐11 magnetic resonance studies of some potassium tetraarylborates
Authors: Vandeberg John T. , Moore Carl E. , Cassaretto Frank P. 
Published: May 2005

AbstractProton and boron‐11 magnetic resonance spectra for several potassium para‐substituted tetraarylborate compounds [KB(C6H4‐pX)4, where X is H, OCH3, CH3, Br, Cl, F, CF3] have been obtained. The chemical shift between the centers of the AA′ and XX′ multiplets for the ring proton multiplets, relative to a reference chemical shift of 0·39 ppm for potassium tetraphenylborate, correlated with the corresponding Hammett σ values for the para‐substituent. Additionally, the boron‐11 chemical shifts gave a good correlation with corresponding σ values for the substituents. Electronegativities of para‐substituted phenyl rings were calculated and found to be approximately 2·70 for all compounds studied. It was shown that electronic substituent effects do not greatly influence the electron density surrounding the central boron atom in the tetraarylborate ions.
Conformations of highly hindered aryl ethers—XVII. Hindered rotation and carbon–halogen bond magnetic anisotropy in benzyl phenyl ethers
Authors: Lehmann F. Pedro A. 
Published: May 2005

AbstractThe PMR spectrum of 3,5‐dibromo‐4‐methoxybenzyl 2′,6′‐dibromo‐4′‐methylphenyl ether shows two aromatic proton
equation image
signals at δ = 7·33 and 7·71. Comparison with related benzyl ethers and anisoles led to assignment of the upfield signal to the phenyl‐ring protons (H3′ and H5′) and the downfield signal to the benzylic aromatic protons (H2 and H6). In view of the nearly identical inductive effects to which they are subjected, their large shift difference must be due to long‐range effects in preferred conformations. Analysis showed that the anomalous shift observed for the benzylic aromatic protons is due to deshielding by both the other aromatic ring and by the carbon‐halogen bonds. The relation of this work to related biphenyls and diphenyl ethers is discussed.
Magnetic nonequivalences in 2,2,4‐trimethylpentane‐1,3‐diol diisobutyrate and diacetate
Authors: Fantazier Richard M. 
Published: May 2005

Abstract2,2,4‐Trimethylpentane‐1,3‐diol diisobutyrate (1) and diacetate (2) exhibit magnetic nonequivalence for both sets of geminal‐dimethyl groups adjacent to the asymmetric center, and nonequivalence of the methylene protons three bonds removed. Solvent and temperature studies indicate that one geminal‐dimethyl moiety is affected only by intramolecular influences, while the other is also subject to solvent effects. The behavior is rationalized in terms of a preferred conformation in which steric effects prevent the interaction of one moiety with solvent. An inverse temperature dependence for methyl nonequivalence is observed for 2 and an absence of a temperature dependence is noted for 1. The unusually large methylene nonequivalences, 23 Hz in 1 and 34 Hz in 2, are attributed to the proximity of an ester carboxylate.
On the alleged correlations between simple LCAO‐MO reactivity indices and proton chemical shifts in planar, condensed, benzenoid hydrocarbons
Authors: Mallion R. B. 
Published: May 2005

AbstractPrevious investigations into the proposed correlations between proton chemical shifts in conjugated hydrocarbons and the various LCAO‐MO ‘reactivity indices’ (at the corresponding carbon atoms to which the peripheral protons are bonded), are here reassessed in the light of more‐recently acquired experimental data, for the case of the planar, alternant, condensed, benzenoid hydrocarbons. A correlation coefficient of 0·73, statistically ‘significant’ at less than the ½% level, is obtained. Nevertheless, there are several unsatisfactory features of such proposed correlations (which are discussed), and, in the final analysis, no causative relation is expected between proton chemical shifts and reactivity indices in these molecules. Furthermore, the relative chemical shifts of the sterically unhindered protons in planar, alternant, benzenoid hydrocarbons can be accounted for by the ‘ring current’ effect alone, without the need to postulate a dependence of the proton chemical shifts on reactivity indices, which is in any case considered to be unlikely on physical grounds.
PMR configurational analysis of pinitol with the aid of lanthanide shift reagents and the homonuclear INDOR technique
Authors: Cavagna F. , Groebel A. 
Published: May 2005

AbstractThe PMR spectrum of the peracetylated O‐methyl‐chiro‐inositol (pinitol) could be analysed by employing lanthanide shift reagents and performing spin‐decoupling and INDOR experiments. The 100 MHz theoretical spectrum has been simulated and good agreement with the experiment has been achieved. Analysis of the vicinal HH‐couplings yields the relative configuration.
Etude de la Barrière de Rotation et du Couplage 5J d'α‐Formylpyrroles Stériquement Encombrés
Authors: Jaureguiberry C. , Fournie‐Zaluski M. C. , Roques B. , Combrisson S. 
Published: May 2005

AbstractLes α‐formylpyrroles substitués sur l'azote par des groupements d'encombrement croissant ne montrent aucune modification sensible dans la valeur du couplage stéréospécifique 5J. Dans les i.Pr‐1 et s.Bu‐1 formyl‐2 pyrroles on met en évidence l'existence d'une conformation préférentielle plane. L'examen des barrières de rotation des dérivés étudiés indique une torsion dans le seul cas du t.Bu‐1 formyl‐2 pyrrole. L'absence de modification de la valeur du couplage 5J dans ce dernier composé est interprêtée par un relais du mécanisme σ—σ par une transmission σ—π.
Transmission of substituent effects in 1,2,3‐selenadiazole derivatives—I
Authors: Caplin G. A. 
Published: May 2005

AbstractChemical shifts are reported for the heterocyclic ring hydrogen of a series of para‐substituted 4‐aryl‐1,2,3‐selenadiazoles and substituent effects are evaluated statistically by means of the Swain‐Lupton multiple correlation analysis. A satisfactory understanding of the various substituent effects is obtained by this approach. Excellent correlations were obtained for a number of varying aliphatic solvents, no serious hindrances to correlation being encountered. An approach was also made towards an understanding of aliphatic‐ and aromatic‐induced solvent shifts, as far as these are modified by substituents.
A comparison of classical and quantum‐mechanical ‘ring‐current’ theories
Authors: Rose P. I. 
Published: May 2005

AbstractThe proton resonance spectra of a series of 2,7‐disubstituted‐4,5‐bis(2‐pyridyl)phenanthrene‐3,6‐diols are examined with emphasis on the shielding effects produced by aromatic ‘ring currents.’ In this series, two pyridine rings are rigidly held less than 3.4 Å apart and with considerable overlap. The ‘ringcurrent’ shieldings found for above‐the‐plane positions are in good agreement with the Johnson‐Bovey theory, whereas a recently proposed quantum‐mechanical theory underestimates the shieldings by a factor of nearly three.
Über die Struktur der Thioamide und ihrer Derivate—XXIII:14N‐Entkoppelte H‐NMR‐Spektren und Messung der Rotationsbarrieren bei primären Amiden und Thioamiden
Authors: Walter W. , Schaumann E. , Rose H. 
Published: May 2005

AbstractDurch Sättigung der 14N‐Resonanz lässt sich in den H‐NMR‐Spektren der primären Amide (1a bis 1d) und der Thioamide (2a bis 2g) die behinderte Rotation um die CN‐Bindung des (Thio)Amid‐Systems nachweisen. Mit Hilfe von Kopplungskonstanten und der Benzolverdünnungsmethode gelingt es, die Signale der Amino‐Gruppe dem cis‐ und dem trans‐NH‐Proton zuzuordnen. Aus der Koaleszenz wird die freie Aktivierungsenthalpie der behinderten Rotation ermittelt und ihre Abhängigkeit von sterischen und elektronischen Effekten sowie vom Lösungsmittel diskutiert.
Diazoalcanephosphonates. Etude par RMN du proton de la configuration de Δ1‐pyrazolines dérivées du norbornadiène
Authors: Cohen Huguette , Benezra Claude 
Published: May 2005

AbstractLes spectres de RMN de onze pyrazolines 1 à 11 dériveés du norbornadiène sont interprétés et discutés. Les configurations des pyrazolines sont déduites du couplage vicinal PCCH10: celui‐ci est de ∼20 Hz dans les dérivés anti et de ∼6,0 Hz dans les dérivés syn. Le couplage à longue distance P,H9 est stéréospécifique, il est maximum pour les épimères syn.
Carbon‐13carbon‐13 coupling constants of 13C‐methyl labeled o‐ and p‐substituted toluenes
Authors: Marshall James L. , Ihrig Arthur M. 
Published: May 2005

AbstractFrom 13C‐7 labeled toluene the following 13C‐methyl o‐ and p‐substituted toluenes were synthesized: o‐NO2, ‐NH2, ‐I and CN; p‐NO2 and ‐NH2. Each of these labeled compounds was studied by carbon magnetic resonance to determine all carbon‐13carbon‐13 splittings involving the methyl carbon.
Electron spin emission phenomena
Authors: Atkins P. W. 
Published: May 2005

AbstractA brief review of a method that has been used to observe transient ESR signals from short‐lived radicals generated photolytically is presented. At short intervals emission spectra are observed, which in the cases studied (aromatic carbonyls in paraffins) show virtually no multiplet effect. One application of this observation is to the direct determination of electron spinlattice relaxation times in liquids. Some of the theoretical problems connected with the polarisation process are described, with particular reference to the role of radical re‐encounters. Some simple analytical expressions for the polarisation are presented.
Quantitative theory of chemically induced dynamic nuclear polarisation in high magnetic fields
Authors: Buchachenko A. L. , Markarian Sh. A. 
Published: May 2005

AbstractFurther development of the diffusional model of the radical pair is suggested. A function is proposed for the exponential distribution of the diffusional trajectories of the radicals in a radical pair. By this function, the differences in the populations of nuclear spin levels in the molecules are calculated for the S, T and U precursor pairs.The equations which express the relationship between the theoretically calculated population differences and the experimentally determined enhancement coefficients are derived.
Carbon‐13 chemical shifts of substituted nortricyclenes
Authors: Lippmaa E. , Pehk T. , Paasivirta J. 
Published: May 2005

Abstract13C NMR spectra of a series of substituted nortricyclene derivatives have been measured, and the 13C chemical shifts interpreted in terms of α, β, γ and δ‐effects. The nature of these substiuent shifts is discussed together with some analytical possibilities. The substituent shifts provide valuable data about the steric effects in strained molecules and can be used as increments for structural analysis, particularly for the determination of orientations of substituent groups.
Nuclear magnetic resonace spectra of substituted oxazoles and oxazolidinones
Authors: Deavenport Dennis L. , Harrison C. H. , Rathburn D. W. 
Published: May 2005

AbstractDuring the synthesis of 2,5‐disubstituted oxazoles and 4‐oxazolidinones, NMR spectroscopy was utilized to obtain information on the structure, bonding and geometric isomerism in the various compounds. Long range couplings between substituents attached at C2 and C5 in both ring systems was of particular utility in this respect. The aromaticity of the oxazole ring is substantiated by the ability of the π system to transmit long range coupling through the ring and by the chemical shifts of the ring protons. Geometric isomers of the 4‐oxazolidinones are identified by observing long‐range cis and trans couplings of the order of 1·8 to 2·4 Hz.
The effect of solute concentration on the chemical shift of aromatic compounds. Some studies using 1‐iodonaphthalene as a model compound
Authors: Ewing D. F. 
Published: May 2005

AbstractThe change in chemical shift with solute concentration (dilution effect) has been determined for a model compound—1‐iodonaphthalene—in cyclohexane and carbon tetrachloride. The data and assignments for this compound differ from those of previous work. A simple model is proposed to account for dilution shifts in aromatic solutes and their sensitivity to proton position. Solvent shifts are also discussed.
Chemical polarisation of electrons in redox reactions
Authors: Shuvalov V. F. , Stunzhas P. A. , Moravskii A. P. 
Published: May 2005

AbstractIn the system Ti(III)H2O2RH (RH is isobutyric acid or isopropanol) the concentration and polarisation of the β‐radical decreases during the reaction, while the polarisation of the α‐radical increases with the decrease of the α‐radical concentration. The second fact is not in accordance with Adrian's model of inducing the polarisation in redox systems during the radical recombination process.
Conformational studies by nuclear magnetic resonance—V:13C spectra and structural problems of enamino carbonyl compounds
Authors: Kozerski Lech , Dabrowski Janusz 
Published: May 2005

AbstractA 13C magnetic resonance investigation of 22 compounds of the general formula OC1(R1)C2(R2)C3(R3) NR4R4′ has been carried out in order to confirm the conformational assignments estimated previously by PMR and IR spectroscopy. The effects of nonplanarity and hindered rotation have been discussed based on chemical shifts and shapes of the C1, C2 and C3 signals.
Sur les conditions de formation des complexes des chloroalkylgallium (ClnR3−nGa) avec diverses bases de Lewis (R2O, R2S, R3N et R3P): étude par spectroscopie de RMN (1H)
Authors: Haran Raymond , Laurent Jean‐Pierre , Commenges Gérard 
Published: May 2005

AbstractUne étude des conditions de formation des complexes résultant de l'addition des bases de Lewis usuelles (R2O, R2S, R3Net R3P) sur les chloroalkylgallium (ClnR3−nGa) a été réalisée à l'aide de la spectroscopie de RMN.Il apparaǐt que les seuls composés à se former à la température ambiante sont des complexes mettant en jeu 1 mole de base et 1 mole d'acide. Leur stabilité est gouvernée par le nombre d'atomes de chlore fixés sur le gallium et par la nature de l'atome donneur.
An NMR study of some substituted 1,3‐ and 1,4‐bistrifluoromethylbenzenes
Authors: Bartle K. D. , Hallas G. , Hepworth J. D. 
Published: May 2005

AbstractContrary to an earlier report, the metallation of 1,3‐bistrifluoromethylbenzene with n‐butyllithium is found to take place at the 4‐ and 2‐positions. Lithiation of 1,4‐bistrifluoromethylbenzene and subsequent carboxylation gives exclusively the 2‐carboxylic acid. Structures are assigned on the basis of PMR data (100 and 220 MHz). The effects of coupling between aromatic protons and trifluoromethyl groups and the aromatic chemical shifts brought about by esterification are discussed for a series of bistrifluoromethylbenzoic acids.
Some aspects of anisochronism of geminal methyl groups in quaternised α‐dimethylamino esters (1H and 13C NMR)
Authors: Da̧browski Janusz , Ejchart Andrzej , Kamieńska‐Trela Krystyna 
Published: May 2005

AbstractThe magnitude of chemical shift nonequivalence (Δδ) in compounds having the general formula R1CH(COOR2)N+R3Me2X− is discussed from the viewpoint of selective shielding of one of the geminal groups by the ester group in the preferred rotamer. In addition, a novel example of the increase of Δδ with rise in temperature has been observed.
31P CIDNP in the reactions of phosphoranyl radicals
Authors: Levin Ya. A. , Il'yasov A. V. , Goldfarb E. I. , Vorkunova E. I. 
Published: May 2005

AbstractThe polarisation of phosphorus nuclei (31P CIDNP) during the free radical reactions of triakyl and triaryl phosphites proceeding via intermediate phosphoranyl radicals is discussed.
Etude par Résonance Magnétique Nucléaire de la thiamine (vitamine B1). Site de protonation‐équilibre de tautomérie
Authors: Fournier J. , Vincent E. J. , Chauvet A. M. , Crevat A. 
Published: May 2005

AbstractNous mettons en évidence l'existence d'un équilibre de tautomérie dans la thiamine et ses esters phosphoriques. Et nous évaluons la position relative de l'équilibre dans ces différents composés. Le calcul permet de relier un grand nombre d'observations expérimentales.
Cyclodimerisation reactions of conjugated dienes with aldehydes—I: Formation of tetrahydropyrans and their 300 MHz 1H NMR spectra
Authors: De Smet A. , Anteunis M. 
Published: May 2005

AbstractThe palladium catalysed reaction of butadiene with aldehydes yields 2‐substituted 3,6‐divinyl‐tetrahydropyrans.1–4 The reaction has been extended to isoprene and myrcene. With formaldehyde only 2,5‐substituted pyrans have been isolated. The isomeric tetrahydropyrans obtained were fully characterised by 1H NMR, and representative 300 MHz spectra are given. Attempts to react aldehydes with 2‐methoxybutadiene were unsuccessful.
Chemically induced dynamic nuclear polarisation in some SE and SN reactions
Authors: Beletskaya I. P. , Rykov S. V. , Buchachenko A. L. 
Published: May 2005

AbstractCIDNP has been found for the methylene protons in Ph3CR (R = C6H5CH2) from the reaction of RHg with Ph3CX. A weak CIDNP effect was observed in the product (CH3O)2C6H3CPh3 of alkylation of veratrol by Ph3CCl (an aromatic SE substitution) and in the Meisenheimer complex resulting from the reaction of (CH3COCH2)2Hg with trinitrobenzene in DMSO in the presence of iodide ions (an aromatic SN substitution).