bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tris(dipivaloylmethanato)europium induced shifts of proton resonances in π‐deficient nitrogen heterocycles
Authors: Armarego W. L. F. , Batterham T. J. , Kershaw J. R. 
Published: May 2005

AbstractTris(dipivaloylmethanato)europium [Eu(DPM)3]induced shifts of the proton resonances of pyridine and its 2‐methyl, 3‐methyl, 2,3‐dimethyl and 2,5‐dimethyl derivatives, pyridazine, pyrimidine, pyrazine, quinoline, isoquinoline, 1,6‐, 1,7‐ and 1,8‐naphthyridine, cinnoline, phthalazine, quinazoline, quinoxaline, 1,4,5‐ and 1,4,6‐triazanaphthalene, pteridine, acridine, phenanthridine and 1, 10‐phenanthroline, have been measured for solutions containing 0·1, 0·3 and 0·5 molar equivalents of Eu(DPM)3. Differences in the behaviour of these heterocycles are discussed in terms of the steric relationship between the heterocycle and the complex. The 3 cos2 ϕ term, present in the expression for calculating pseudo‐contact shifts, is shown to be important. The order of basicity of these heterocycles, as measured by their pKa values, cannot be used to predict the order of Eu(DPM)3 induced chemical shifts.
Proton magnetic resonance spectrum of thiophen dissolved in a nematic solvent
Authors: Dereppe Jean‐Marie , Morisse Jean‐Pierre , Van Meerssche Maurice 
Published: May 2005

AbstractThe PMR spectrum of thiophen dissolved in a nematic phase is reported. This spectrum has been analysed iteratively. The ratios of the various inter‐proton distances determined in this study are in good agreement with those previously reported.
14N chemical shifts in the enamino ketone quaternary ammonium salts
Authors: Dąbrowski Janusz , Kamieńska‐trela Krystyna , Sadlej Andrzej J. 
Published: May 2005

AbstractThe 14N chemical shifts were measured for a series of quaternary ammonium salts of enamino ketones. An upfield shift of the 14N resonance signals upon quaternization has been observed. The interpretation in terms of the approximate theory of nuclear magnetic shielding is given. The calculations for some model systems result in a general agreement with the experimental data.
Spectroscopic studies on N, N‐dimethylamides—IV An NMR total line shape study of substituent effects and medium effects on amide‐rotational barriers of N,N‐dimethylbenzamides and ‐cinnamamides
Authors: Spaargaren K. , Korver P. K. , Van Haak P. J. Der , de Boer Th. J. 
Published: May 2005

AbstractAmide‐rotational barriers obtained with a total line shape analysis of a series of para‐substituted N,N‐dimethylbenzamides and ‐cinnamamides are correlated with the result of an H. M. O. (Ω = 1·4) calculation. There is no difference in the activation parameters at a concentration of 0·25 M and 1 M in CDCI3 as a solvent.Despite the lower solvent polarity of chloroform (ε = 4·7) compared with acetonitrile (ε = 37·5) the rotational barriers in both solvents are about equal, probably due to hydrogen bonding in chloroform.The amide rotation rate appears to be very sensitive to traces of hydrochloric acid in a non‐basic solvent like chloroform.
Conformational analysis of 1,2:5,6‐diepithio‐3,4‐di‐o‐acetyl‐hexitols
Authors: Sohár P. , Kuszmann J. 
Published: May 2005

AbstractConformational studies of acetylated open chain hexitol derivatives, possessing similar structures but differing in their configuration have been made by analysing their NMR spectra. It is shown, that the carbon chain of all three (manno‐, ido‐and gluco‐) isomers is present in a non planar non zig‐zag conformation, containing the acetoxy groups at C‐3 and C‐4 in a trans relation.
Constantes de Couplage en Serie Pyridinique. Application de la Theorie des Orbitales Moleculaires
Authors: Dorie J. P. , Martin M. L. , Barnier S. , Blain M. , Odiot S. 
Published: May 2005

AbstractLes constantes de couplages relatives à un ensemble de 35 pyridines substituées sont discutées en relation avec les propriétés électroniques des substituants et le mécanisme du couplage. Un calcul de J est réalisé, sur la base de la théorie de Pople, à l′aide des valeurs de polarisabilités mutuelles obtenues par la méthode CNDO/2 et la méthode d'Hoffmann. L'influence d′une inclusion des intégrales bicentriques est examinée.
Carbon‐13 chemical shifts of monosubstituted cyclohexanes
Authors: Pehk T. , Lippmaa E. 
Published: May 2005

AbstractThe carbon‐13 chemical shifts of monosubstituted cyclohexane derivatives are compared with those of aliphatic compounds. The polar substituents exert a similar influence on the α‐, β‐ and γ‐carbons in both series of compounds. The δ‐effect is shown to be characteristic mainly to the cyclic compounds, however. The appearance of a δ‐effect is discussed as a possible consequence of electron delocalization in alicyclic molecules. A correlation of these δ‐effects with inductive parameters of the substituents is presented.
A new N‐alkylation reaction—V: NMR investigations
Authors: Sohár P. , Reiter J. , Toldy L. 
Published: May 2005

AbstractThe structure elucidation of some isomeric imidazo(1,2‐a)pyrimidones by NMR spectroscopy is described. The tautomerism of the compounds with non‐substituted nitrogen is also discussed.
Dimers from α‐alkoxybenzyl radicals. An NMR study
Authors: Goh S. H. , Ong S. H. , Sieh Iling 
Published: May 2005

Abstractmeso and dl Dimers (ArCHOR)2 where R is Me, Et, iPr, tBu, cyclohexyl and 1‐adamantyl may readily be differentiated by their NMR spectra; the benzylic protons of the meso isomer always absorb at a slightly higher field than those of the dl isomer in each of the solvents used. Differences in chemical shift are discussed in terms of preferences in conformer distribution. The formation of equal amounts of both dimers from the corresponding radical ArCHOR shows that steric and polar factors are not important in influencing the dimerization. Magnetic non‐equivalence due to the presence of asymmetric centres was found in some of the compounds discussed above.
The accidental equivalence of protons in 3‐hydroxy‐3‐methylbutyrolactone: Solvent and temperature dependence
Authors: Firth Bruce E. , Singh S. P. , Kagan Jacques 
Published: May 2005

AbstractThe temperature or the nature of the solvent selectively affects the NMR equivalence of the protons at C‐2 and C‐4 in 1.
Hindered rotation in thioamides—II
Authors: Ramey Kermit C. , Louick David J. , Whitehurst Philip W. , Wise William B. , Mukherjee Rabindranath , Rosen John F. , Moriarty Robert M. 
Published: May 2005

AbstractThe NMR spectra for a series of amides and thioamides of type magnified image where R = CH3, C6H5 and C6H5CH2, were investigated from −60° to 150°C. The Arrhenius activation energies, Ea, for the normal amide equilibration were determined by the W½ method and the values range from 15.4 to 20.9 Kcal/mole.The three thioamides, compounds (2), (4) and (6) yield spectra showing a second, low temperature, equilibration. This exchange was first studied by Siddall and co‐workers and they interpreted the spectral changes in terms of population changes of the conformational isomers about the NCH bonds. They assumed strong interaction of nitrogen alkyl groups which gave rise to three low energy dl pairs of isomers. Their results, however, as well as those obtained for similar compounds reported herein, show only two sets of patterns at low temperatures. These spectra suggest a first order, A⇄B, type equilibration where PA≠PB. An alternative assignment based upon the following classification of steric effects of S, R, R′ and R″, magnified image is suggested; (1) a strong interaction of the sulfur atom with the adjacent alkyl group on the nitrogen atom, R′, (2) a somewhat weaker interaction of R with the adjacent nitrogen alkyl group R″ and (3) a still weaker interaction of the two nitrogen alkyl groups, R′ and R″. This leads to four isomers, two dl pairs, C1T4, C6T3 and C1T6, C6T3, which are expected to have a lower energy than the rest and the first pair is preferred.The W½ method of measuring exchange rates was extended to cover A⇄B equilibrations, where PA≠PB. The results indicate an accuracy that is not significantly lower than that obtained by the more elaborate total line shape analysis.
The molecular structure and unusual orientation of phenol in a liquid crystal solevent as determined by NMR spectroscopy
Authors: Diehl P. , Henrichs P. M. 
Published: May 2005

AbstractThe NMR spectrum of phenol, dissolved in a nematic solvent, is explainable in terms of two averaging planar structures for each of which the principle axis of orientation in the ring is on the opposite side of the oxygen atom from the hydroxyl proton. External hydrogen bonding to the solvent seems to be an important factor in determining the orientation. The molecular structure obtained is compared with those found by microwave spectroscopy and X‐ray diffraction.
Chemical polarization of nuclei. Proton polarization during thermal decomposition reaction of dimethyl perdiglutarate
Authors: Ignatenko A. V. , Kessenikh A. V. 
Published: May 2005

AbstractProton chemical polarization was observed in methyl butyrate, γ‐butyrolactone and in some other products of the dimethyl perdiglutarate decomposition reaction. The polarization pattern of the α‐CH2 and β‐CH2 groups in butyrolactone is just as one would expect in the products of the CH3OCH2CH2ĊH2 radical which has left the pair of identical radicals. Thus butyrolactone is formed from the CH3OCH2CH2ĊH2 radical by means of intramolecular cyclization and elimination of the methyl radical.
Determination of the rate of intramolecular exchange between two complex spin systems from the NMR spectra
Authors: Derendyaev B. G. 
Published: May 2005

AbstractReversible 1,2‐shifts of the ethyl group in the 9‐ethyl‐9, 10‐dimethylphenanthrenonium ion lead to a reversible change of the ring hydrogen states (A′B′C′D′ ⇄ A″B″C″D″). Line shape analysis for the determination of the exchange rate was performed for this case of intramolecular exchange between the two multi‐spin systems. The calculations are based on density matrix formalism.
AB‐based NMR systems. Choice of bounds for θ in trigonometric forms of co‐factors in mixed wave‐functions
Authors: Batterham T. J. , Bigum C. J. 
Published: May 2005

AbstractLabelling problems associated with the choice of bounds for the angle θ in the trigonometric forms of the co‐factor expressions for levels in AB‐based NMR spectra have been investigated. It has been shown that any pair of octants within the 0 → 2π range can be specified as bounds, provided that appropriate linear combinations of wave functions are chosen. The range 0 ⩽ θ ⩽ π/2 is preferred for simplicity in calculation.
NMR‐spectra of 1‐[2,4,5‐triphenylcyclopentenyl] phenyl ketones
Authors: Wawzonek S. , Bennett W. E. 
Published: May 2005

AbstractNMR‐Spectra of 1‐[2,4,5‐triphenyl‐2‐cyclopentenyl]phenyl ketone and 1‐[2,4,5‐triphenyl‐1‐cyclopentenyl]phenyl ketone indicate that the coupling constants of vicinal hydrogens in the cyclopentene ring vary with structure.
Barriers to internal rotation in 1,3,5‐trineopentylbenzenes—II: Unsymmetrically halogen‐substituted compounds
Authors: Nilsson Bertil , Carter Robert E. , Dahlqvist Kjell‐Ivar , Márton József 
Published: May 2005

AbstractThe temperature dependence of the three different methylene AB spectra due to the 1‐, 3‐ and 5‐neopentyl groups in 2‐chloro‐4‐iodo, 2‐bromo‐4‐iodo and 2‐bromo‐4‐chloro‐1,3,5‐trineopentyl‐benzene was studied by proton magenetic resonance measurements at 60 MHz. The identification of the lines of the AB quartets at low temperature was carried out on an HA‐100 spectrometer by means of the INDOR technique. The activation parameters for all three barriers in each compound were found to be approximately the same, which perhaps reflects the interdependence of the rotations, with the smaller of the two halogens determining the size of the barrier. An explanation in terms of magnetic nonequivalence induced in the 1‐ and 5‐methylenes by the 3‐neopentyl group is considered to be most plausible.
Conformational effects in cyclic imino acids—I: The NMR spectra and conformations of l‐azetidine‐2‐carboxylic acid and its N‐acetyl derivative
Authors: Thomas W. A. , Williams M. K. 
Published: May 2005

AbstractThe complete analysis of the PMR spectrum of azetidine‐2‐carboxylic acid is reported and conclusions made regarding the conformation of the molecule in aqueous solution. the effect of N‐acetylation on chemical shifts, coupling constants and hence conformation is investigated, and the geometric isomer ratio and energy barrier to rotation about the amide bond determined.
13C, 14N, 15N and 17O NMR spectra of the charged species of nitropyrroles and nitroimidazoles
Authors: Lippmaa E. , Mägi M. , Novikov S. S. , Khmelnitski L. I. , Prihodko A. S. , Lebedev O. V. , Epishina L. V. 
Published: May 2005

AbstractChanges in 13C and 14N chemical shifts of the nitro derivatives of nitrogen heterocycles upon ionization (anion or cation formation) are twofold—first a uniform paramagnetic or in the case of protonation, a uniform diamagnetic shift of all the ring resonances that parallels the changes in the respective ultraviolet spectra and must be caused by changes in the molecular excited states, and second—the influence of the conjugated nitro group. About one third of the total negative anion charge may be localized on the nitro group, which causes unusually large shifts of the ring 13C resonances in this case.
v‐Triazolines—IV: NMR configuration assignment of 5‐dialkylamino‐v‐triazolines
Authors: Stradi Riccardo , Pocar Donato , Bianchetti Giuseppe 
Published: May 2005

AbstractA series of 1‐aryl‐5‐amino‐4,5‐dihydro‐v‐triazoles bearing at least one hydrogen atom at the C‐4 position has been prepared. The NMR features of the above compounds have been studied with the purpose of differentiating the triazolines with a trans configuration from those with a cis configuration. It has been shown that the hydrogen atom at C‐4 lying on the same side of the amine group at C‐5 always resonates at lower field than the hydrogen atom on the opposite side. This rule can be applied for identifying the configuration of the 5‐amino‐v‐triazolines.
Conformational studies by nuclear magnetic resonance—III: ASIS and protonation studies of the rotational isomerism of enamino aldehydes and ketones
Authors: Kozerski Lech , Dąbrowski Janusz 
Published: May 2005

AbstractThes‐cis⇌s‐transequilibrium of several enamino ketones and aldehydes,equation imagehas been evaluated based on the results of aromatic solvent induced shift measurements and of protonation of the title compounds. In contrast to α,β‐unsaturated ketones bearing no heteroatom, the Δδ3,cisvalue but not the Δδ3,trans, proved to be useful in conformational assignments. Protonation, which occurs mainly on oxygen, enhances the rotational barrier, thus enabling the observation of both rotamers at room temperature. Steric hindrance to conjugation enhances the rate of protonation at the carbon C2.
C‐13 chemical shifts of the carbonyl group—VI: Transannular interactions in mesocyclic compounds
Authors: Nakashima Thomas T. , Maciel Gary E. 
Published: May 2005

AbstractThe utility of C‐13 NMR in detecting transannular interactions of a carbonyl group with O, S and N in eight‐membered ring compounds has been studied. The C‐13 carbonyl chemical shifts were determined in two solvents, employing frequency‐sweep and pulse/Fourier transform techniques. The results confirm earlier conclusions based upon other physical methods and indicate that C‐13 NMR should prove useful in studies of such interactions.
Chemical shift assignments in N,N‐disubstituted trifluoroacetamides
Authors: Graham Laurine L. 
Published: May 2005

AbstractDue to hindered rotation about the central CN bond in N,N‐disubstituted trifluoroacetamides, CF3CONR1R2, two resonance peaks are usually observed for each proton in R1 and R2. Chemical shift assignments are made for the following amides: 1, R1 = R2 = Me; 2, R1 = R2 = Et; 3, R1 = Me, R2 = 2‐Propyl; 4, R1 = Me, R2 = 1‐Butyl; 5, R1 = Me, R2 = Cyclohexyl; 6, R1 = R2 = 2‐Propyl; 7, R1 = 2‐Propyl, R2 = Cyclohexyl. Amides 6 and 7 show an inversion of the relative chemical shift for both the methine and methyl protons of the 2‐propyl group as compared with 3. For non‐fluorinated amides, aromatic solvents shift the trans alkyl peaks to higher field faster than those cis (to the carbonyl oxygen atom); however, this generalization does not apply to all trifluoroacetamide proton peaks.
Conformational studies by nuclear magnetic resonance—IV: Restricted rotation in vinylogous thioamides
Authors: Dabrowski Janusz , Kamieńska‐Trela Krystyna 
Published: May 2005

AbstractEnamino ‐thial and ‐thiones R1C(S)CHCHNR (R1 = H or alkyl; R2 = Me or Et) have been shown by NMR spectra to exist in two rotational forms, s‐cis and s‐trans, the populations of the latter being approximately the same as in the case of the parent oxa analogues. An increase of the order of 2 to 4 Kcal/mole in the heights of CC and CN rotation barriers (ΔG*) was found on comparing the title compounds with their oxa analogues. IR spectra failed as a tool to establish the rotational equilibrium. IR absorption bands of the νCC, νCH (in the NMe2 group) and γHCCH vibrations have been found, but the νCS band could not be assigned unambiguously. Anomalies concerning the frequency and intensity of the νCC band are discussed.
The conformation of meso and racemic 2,3,4‐trichloropentanes—model compounds for polymers derived from 1,2‐dichloroethylenes
Authors: Clifford R. P. , Ewing D. F. 
Published: May 2005

AbstractOn the basis of coupling constants and chemical shifts the conformation of meso and racemic 2,3,4‐trichloropentanes have been determined. The meso isomer exists as an equilibrium between the expected rotameric forms but the racemic isomer is anomalous and exists almost entirely as a distorted form of a rotamer which has parallel 1:3 interactions. The significance of these conformations is discussed in relation to the likely conformation and stability of the corresponding stereoregular polymers, which may be derived from cis‐ and trans‐1, 2‐dichloroethylene.
Barriers to rotation about CN bonds—I: Rotation about the CN bond in mono‐, di‐ and trifluoroacetamide, and deuterium isotope effects upon 19F shielding
Authors: Pendlebury M. H. , Phillips L. 
Published: May 2005

AbstractThe 19F NMR spectra of mono‐ and difluoroacetamide are used to derive the activation parameters for rotation about the CN bond; it is not possible to obtain useful results for trifluoroacetamide. A total line shape analysis is used.Unusually large deuterium isotope effects upon the shielding of the 19F nucleus are observed for N‐deuterated derivatives. The magnitude of the isotope effect is different for mono‐, di‐ and trifluoroacetamides, and in the mono‐deuterated species the isotope effect is different for cis and trans rotational isomers.
Lanthanide induced paramagnetic shifts—derivation of equilibrium constants and absolute shifts in Eu(DPM)3 systems
Authors: Mackie R. K. , Shepherd T. M. 
Published: May 2005

AbstractRelationships between the magnitude of induced 1H NMR shifts and the equilibrium conditions in solutions containing lanthanide shift reagents are discussed and applied to the shifts induced in several organic molecules by Eu(DPM)3. Evidence that monoadduct formation is the predominant equilibrium in these solutions, and values of absolute shifts and equilibrium constants are reported. The results indicate that a contact mechanism makes the major contribution to the observed shifts in 4‐methylpyridine. In the case of 2,4,6‐trimethylpyridine the observed shifts are largely pseudocontact in origin.
The decomposition of 1‐phenyl‐3‐chloro‐nortricyclene and 1‐phenylnortricyclene on reduction in 1,2‐dimethoxyethane. The EPR spectra of the radical ions
Authors: Eloranta Jorma , Paasivirta Jaakko , Moilanen Reijo , Vesterinen Raili 
Published: May 2005

AbstractRadical anions of 1‐phenyl‐3‐chloronortricyclene and 1‐phenylnortricyclene were produced by reduction with potassium in 1,2‐dimethoxyethane under a high vacuum. The initially formed radical anion of 1‐phenyl‐3‐chloronortricyclene was very unstable, and decomposed finally to the anions of naphthalene and biphenyl. The only product of the reduction of 1‐phenylnortricyclene was the biphenyl anion. The EPR spectra of the reaction mixtures were measured at temperatures from —80°C to room temperature.
Characterization of di‐ and trimethoxybenzaldehydes by analysis of deshielding gradients obtained with Eu(fod)3 shift reagent
Authors: Neville G. A. 
Published: May 2005

AbstractEu(fod)3 shift reagent was used to simplify PMR spectra from isomeric mono‐, di and trimethoxybenzaldehydes. Deshielding gradients, obtained by plotting induced shift vs. molar ratio of [Eu(fod)3]/[substrate] made it possible to assign methoxyl proton signals to the correct positional substituent in polymethoxylated benzaldehydes. Anomalous upfield shifts for the aldehydic protons of 2,6‐dimethoxy‐ and 2,4,6‐trimethoxybenzaldehyde were observed with Eu(fod)3 Various instances of long‐range (5J) proton coupling between the aldehydic proton and a meta‐proton provide insight to the geometry of the substrate in the complexed state with Eu(fod)3. Di‐ and trimethoxybenzaldehydes are important precursors for the synthesis of the correspondingly methoxylated amphetamines which are of pharmacological and forensic interest because of abuse and illicit manufacture.
Heterocycles Contenant du Phosphore—XII: Etude par Resonance Magnetique Nucleaire des Oxo‐ et Thio‐2 Phenoxy‐2 Trimethyl‐3,5,5 Oxazaphosphorinanes‐1,3,2. Un Cas Particulier de Systeme ABXY
Authors: Durrieu Josiane , Kraemer Raymond , Navech Jacques 
Published: May 2005

AbstractLes deux oxazaphosphorinanes‐1,3,2 étudiés ici donnent des spectres de RMP qui, après élimination des couplages entre les protons et le phosphore, peuvent e'tre analysés comme des ABXY dans lesquels certaines constantes de couplage sont nulles. Le cas particulier de système ABXY où JAY = JBX = 0 est étudié et on donne l'expression des niveaux d'énergie E7, E8, E9 et E10 et de la fréquence des transitions qui leur sont liées. Des expériences d'INDOR permettent de déterminer le signe relatif des constantes de couplage 3JP–OCH et 3JPNCH. Les résultats expérimentaux permettent de montrer que ces deux oxazaphosphorinanes‐1,3,2 se présentent dans une conformation chaise et que, si équilibre il y a, cet équilibre est très nettement en faveur d'un conformère privilégié.
Nuclear magnetic resonance spectra of codeine and isocodeine derivatives
Authors: Jacobson Arthur E. , Yeh Herman J. C. , Sargent Lewis J. 
Published: May 2005

AbstractThe NMR spectra of a spiro oxirane (1) derivative of codeinone, codeine (2), isocodeine (3), 6‐methylcodeine (4) and 6‐methylisocodeine (5) were compared. NOE and double‐resonance experiments were used to confirm the conformation of 1, and the configuration about C‐6 of 6‐methylcodeine and 6‐methylisocodeine. An interchange of the chemical shifts of the olefinic protons in 1 was noted, as compared with those in all of the other compounds. This interchange could be attributed to the bond anisotropies of the oxirane moiety.
Two‐frequency spin echo in molecular crystals
Authors: Grechishkin V. S. , Shishkin E. M. 
Published: May 2005

AbstractThe two‐frequency pulse response of a multilevel system in NQR is investigated. Additional spin echo signals are shown to appear. The application of the two‐frequency spin echo method to some of the crystals is demonstrated. The method is of great value for the investigation of local fields in crystals.
Dioxidobutane: A comparison between high field and Eu‐shifted PMR spectra
Authors: Gatti G. , Demoarco A. 
Published: May 2005

AbstractComplete analysis of the high field spectrum of the title compound gives well determined parameters in all cases; the value of the CHCH coupling is in agreement with free rotation around this bond. In contrast, the Eu‐shifted spectrum does not allow such a complete analysis because of lack of resolution. Shift dependence on concentration and temperature is reported and discussed.