bluuebunny/crossref_metadata_2025_split huggingface dataset:
New 2‐substituted pyrroline‐N‐oxides: An EPR solvent study of the radical spin adducts
Authors: Janzen Edward G. , Zhang Yong‐Kang , Haire D. Lawrence 
Published: May 2005

AbstractTen substituted 5,5‐dimethyl‐1‐pyrroline‐N‐oxides as well as the parent nitrene spin trap (DMPO) were prepared: 5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2,5,5‐trimethyl‐1‐pyrroline‐N‐oxide, 2‐tert‐butyl‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐phenyl‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐d5‐phenyl‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐phenyl‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide‐nitronyl‐13 C, 2‐(4‐fluorophenyl)‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐(4‐chlorophenyl)‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐(4‐tert‐butylphenyl)‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐(4‐methylphenyl‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide) and 2‐(2‐ methylphenyl)‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide. Analytical (i.e. EPR‐grade) samples of these novel cyclic nitrones were obtained and characterized by (among other methods) 1H NMR spectroscopy. Reduction of DMPO and these various 2‐substituted cyclic nitrones gave the corresponding cyclic N,N‐dialkylhydroxylamines, whose structures and conformations were also analyzed by 1H NMR spectroscopy. Air oxidation of these cyclic N,N‐dialkylhydroxylamines provided access to the EPR spectra of the hydrogen, methyl, tert‐butyl, phenyl, d5‐phenyl, nitronyl‐13C‐phenyl, 4‐fluorophenyl, 4‐chlorophenyl, 4‐tert‐butylphenyl, 4‐methylphenyl and 2‐methylphenyl cyclic aminoxyl (pyrrolidine N‐oxyl nitroxide) radical spin adducts of DMPO. The 14N, 13C (where applicable) and 1H hyperfine splitting constants of these aminoxyl adducts in ten solvents of widely different polarities (e.g., hexane to water) were measured and the solvent effect on these parameters was evaluated. It was found that for the various 2‐substituted DMPO‐type spin adducts both the nitrogen and β‐hydrogen EPR hyperfine splittings correlated linearly (r2 ⩾ 0.90) with typical solvent polarity parameters such as ET(30). The correlation between the nitrogen and β‐hydrogen hyperfine splitting constants were even more linear (r2 ⩾ 0.97).
First discrimination of enantiomeric cyclic hemiacetals and methyl acetals derived from hydroxamic acids and lactams of Gramineae by means of 1H NMR using various chiral solvating agents
Authors: Klein Jens , Hartenstein Holger , Sicker Dieter 
Published: May 2005

AbstractThe discrimination of enantiomeric cyclic hemiacetals and methyl acetals derived from hydroxamic acids and lactams with the 2H‐1,4‐benzoxazin‐3(4H)‐one and 2H‐1,4‐benzothiazin‐3(4H)‐one skeleton was investigated using (S)‐(−)‐phenylethylamine, (−)‐quinine, β‐cyclodextrin and, for the first time, (5R,11R)‐(+)‐2,8‐dimethyl‐6H,12H‐5,11‐ methanodibezo [b,f] [1,5]diazocine, a Troeger's base enantiomer, as chiral solvating agents (CSA). Conditions for the enantiomeric discrimination of six configurationally stable methyl acetals are reported. 2,4‐Dihydroxy‐2H‐1,4‐benzoxazin‐3(4H)‐one and its 7‐methoxy derivative, bioactive aglucones from Gramineae species, are the first cyclic hemiacetals that could be differentiated into enantiomers by means of 1H NMR, despite their oxo–cyclo tautomerization that prevented enantioseparation by chromatography or capillary electrophoresis. However, 2‐hydroxy‐2H‐1,4‐benzothiazin‐3(4H)‐ones (thiohemiacetals) could not be differentiated by the use of these CSA. The influence of the structure of the enantiomers, CSA, temperature and concentration on the size of the chemical shift anisochrony is discussed.
13C NMR Data for abieta‐8,11,13‐triene diterpenoids
Authors: Corral J. M. Miguel Del , Gordaliza M. , Salinero M. A. , Feliciano A. San 
Published: May 2005

Abstract13C NMR spectral assignments for a number of naturally occurring and hemi‐synthetic abieta‐8,11,13‐triene diterpe‐noids are reported. The most significant effects caused by common structural variations for this kind of compound are discussed.
Electric field effects on the shielding of protons in CH bonds
Authors: Grayson Martin , Raynes William Thomas 
Published: May 2005

AbstractThe coefficients which determine the electric field dependence at first and second order of the shielding of protons in CH bonds were calculated by a finite‐field SCF method for the molecules, CH4, C2H6, CH3F, CH3Cl, CH3CN, C2H4, H2CO, HCN and C2H2. Values are given for individual tensor components and for the rotationally averaged coefficients. Diamagnetic and paramagnetic parts of the coefficients are generally of the same order of magnitude. This differs from carbon, nitrogen, oxygen and fluorine shielding studied previously where the paramagnetic parts are often very much larger than their diamagnetic counterparts. The linear electric field coefficients Az (electric field along the CH bond from C to H) for the above molecules (except H2CO and HCN) are very similar in value, with a mean of 70.0 ppm a.u. This is very close to an empirical value of 72.2 ppm a.u. obtained by Zürcher in a classic study of steroids. It further appears that the value may be transferable among all C(sp3)H bonds. A representative value for the mean quadratic coefficient B is 68.0 ppm a.u. Empirical values of this vary widely.
High‐resolution solid‐state 23Na NMR of anhydrous sodium sulfite
Authors: Power William P. 
Published: May 2005

AbstractHigh‐speed magic angle spinning at high magnetic field was used to obtain high‐resolution solid‐state 23Na NMR spectra of anhydrous Na2SO3 (P3, Z = 2). Observation of the spinning sidebands of the 23Na satellite (± 3/2 ↔ ± 1/2) transitions allows the identification of the three crystallographic sites that could not be distinguished in the central transition region of the NMR spectrum. The 23Na sites in this salt were characterized by NMR for the first time and assigned to the crystallographic sites on the basis of a point‐charge model of the electric field gradient tensors at each site.
13C and 1H NMR studies of nitrogen inversion and molecular flexibility in the tricyclic antidepressant drug trimipramine maleate
Authors: Wilson Jennifer C. , Munro Sharon L. A. , Craik David J. 
Published: May 2005

AbstractThe solution conformations and dynamics of the antidepressant drug trimipramine maleate were investigated by 1H and 13C NMR spectroscopy. Of particular interest was an observed non‐equivalence of the N‐methyl groups in the aliphatic side‐chain of the drug, which is present in both 1H and 13C spectra under a range of aqueous and non‐aqueous solvent conditions when the terminal nitrogen is protonated. Although the inequivalence was first observed for the maleate salt, the nature of the counter ion is not a determining factor. The solution concentration of the drug does, however, modulate the observed inequivalence, with the two peaks coalescing at higher drug concentrations. The diastereotopic environments of the two methyl groups arise because of a chiral centre in the aliphatic side‐chain. Inversion of the terminal nitrogen produces exchange between the two environments, thereby destroying the inequivalence and leading to a single averaged resonance for the two methyl groups. The energy barrier for the exchange process was determined from variable‐temperature NMR experiments to be 16.3 kcal ml−1 (1 kcal = 4.184 kJ). This is higher than would be expected for simple inversion of a tertiary nitrogen, but reflects the fact that inversion can only occur for the small fraction of molecules which are not protonated. The barrier determined from the variable‐temperature experiments was in agreement with rates of interchange between the two methyl environments determined from saturation transfer experiments. These rates were measured for a series of different protonation states of the nitrogen, with the rate contant for interchange of environments decreasing with an increasing degree of nitrogen protonation. 13C spin‐lattice relaxation times and nuclear Overhauser enhancement effects were also measured to determine the degree of mobility in the aliphatic side‐chain of trimipramine maleate.
Correlation analysis of 31P NMR chemical shifts with substituent effects of phenols
Authors: Jiang Zhi‐Hua , Argyropoulos Dimitris S. , Granata Alessandro 
Published: May 2005

AbstractOver 60 lignin‐related model compounds were phosphitylated with 2‐chloro‐4,4,5,5‐tetramethyldioxaphospholane, a sterically hindered analogue of 2‐chloro‐1,3,2‐dioxaphospholane used in earlier work, and their 31P chemical shifts were recorded. Excellent resolution between the chemical shifts of phosphitylated carboxylic acids, phenols and aliphatic alcohols was obtained. The correlations of the phosphorus chemical shifts with the chemical environments of lignin‐related phenols using the Hammett principles provided an excellent linear relationship between the resonance substituent constant, σ, and the corresponding 31P NMR chemical shift values for para‐substituted lignin‐related phenols. In addition, a correlation between 31P NMR chemical shifts for ortho‐ and para‐substituted phosphitylated phenols was obtained. A set of empirical parameters that permits the accurate prediction of 31P NMR chemical shifts of lignin‐related phenolic compounds derivatized with 2‐chloro‐4,4,5,5‐tetramethyldioxaphospholane was thus obtained.
Determination of heteronuclear long‐range H,X coupling constants from gradient‐selected HMBC spectra
Authors: Willker Wieland , Leibfritz Dieter 
Published: May 2005

AbstractA gradient‐selected J‐HMBC experiment is presented. Coherence selection with magnetic field gradients results in HMBC spectra in which t1 noise is very low or completely eliminated. This makes it possible to detect unequivocally very small (<2 Hz) long‐range H,X coupling constants. With a slight modification, the HMBC experiment can be used for the quantitative measurement of these couplings. The signal amplitude of spectra with increasing coupling evolution time τ shows the characteristic sin (πJXHτ) dependence. By fitting a sine curve to the experimental data or by performing a 3D J‐resolved HMBC experiment, accurate nJXH coupling constants are obtained. This method is especially useful for estimating coupling constants between protons and unprotonated heteronuclei, e.g. quaternary carbons, 15N nuclei in labelled prolines or 31P in organophosphates.
NMR of terminal oxygen. 16—17O NMR of amide‐analogous N‐acyl derivatives of non‐basic nitrogen groups: The question of amide resonances
Authors: Dahn Hans , Van Toan Vien , Péchy Peter 
Published: May 2005

AbstractNatural abundance 17O NMR data for six classes of N‐acyl compounds RCONX are reported: acylazide, acylisocyanate, acylisothiocyanate, diacyldiimide, 1‐acylimidazole and N,N′‐carbonyldiimidazole. Compared with the normal amide group, they all show strong deshielding (Δδ ≈︁ 70–130 ppm), which is attributed to diminished resonance of the CO group with the weaker electron donor NX. The high shielding of isocyanate oxygen is attributed to symmetry‐based anisotropy effects.
NMR solvent effect study of pyrroline‐N‐oxide spin traps: Microenvironments in sodium dodecyl sulfate micelles
Authors: Haire D. Lawrence , Janzen Edward G. , Robinson Valerie J. , Zhang Yong‐Kang 
Published: May 2005

AbstractComplete 13C NMR assignments for ten five‐membered ring nitrone (pyrroline‐N‐oxide) spin traps in CHCl3 are presented. A good correlation between the nitronyl 13C NMR chemical shift (δ) and the substituent constant (σ) for the substituted phenyl DMPOs was found. The 13C NMR chemical shift of the nitronyl carbon of these 5,5‐dimethyl‐2‐phenylpyrroline‐N‐oxides (or phenyl‐DMPOs) exhibited a large solvent effect (14 ppm from cyclohexane to water) which could be correlated with the solvent polarity parameter ET(30). Using a paramagnetic relaxation agent, the weighted time‐averaged fast exchange of the nitrone between the interior of a sodium dodecyl sulfate micelle and the bulk aqueous phase could be determined. It was found that the 2‐phenylpyrroline‐N‐oxides reside in microenvironments with polarities close to that of ethanol, methanol and between methanol and water. The fraction of nitrone completely inside the micelle at any given time was found to be around 77 ± 0.05%. This is the first time that the paramagnetic relaxation enhancement method has been used with 13C NMR spin‐lattice relaxation time measurements.
Substituent‐effect additivity in 1‐X‐, 2‐X‐ and 1,2‐di‐X‐9,10‐anthraquinone series, a tool for 13C NMR chemical shift assignment
Authors: Danielsen Knut 
Published: May 2005

AbstractThe 13C and 1H NMR spectra of 1‐OH‐, 2‐OH‐, 1,2‐diOH‐, 1‐OAc‐, 2‐OAc‐ and 1,2‐diOAc‐9,10‐anthraquinone were assigned. The hypothesis that substituent‐effect additivity could be used as a chemical shift assignment tool was tested, with satisfactory results. For all compounds, errors were found in previous assignments. The NOE technique combined with SEFT, heteronuclear decoupling and 2D heteronuclear one‐bond correlation experiments were used for the assignment of the different resonances.
31P NMR—structure correlations for phosphonocarboxylic acids and esters
Authors: Olagnon‐Bourgeot Sabine , Chastrette Francine , Wilhelm Didier 
Published: May 2005

Abstract31P chemical shift‐structure correlations were established from methyl and ethyl esters of simple phosphonocarboxylic acids. The influence of solvent, acidity, function and neighbourhood of phosphorus was studied. The correlations could be extended and led to the identification of esters obtained when a series of phosphonocarboxylic acids were reacted with alcohols—reactions which were designed as models of cellulose cross‐linking by these acids.
A NMR study of phenol self‐association. The quasi‐chemical approximation
Authors: Kimtys L. , Mikulskis P. , Shape'ko N. N. 
Published: May 2005

AbstractThe NMR dilution chemical shifts of phenol in the cyclohexane, methylcyclohexane and carbon tetrachloride solutions at temperatures +10, +20, +40, +50, +60, +70 and +80°C have been interpreted applying the quasi‐chemical approximation. The interchange energies for the OH…O bonding and the chemical shifts of hydroxylic protons in associated phenol molecules have been determined and their temperature dependences studied.The obtained results are in good accordance with the equilibrium calculation data.
Kernresonanzuntersuchungen am 1,10‐Phenanthrolin und seinen Komplexverbindungen—V: Zum Ligandenaustausch an einigen diamagnetischen Phenanthrolin‐Komplexen
Authors: Bendorf G. , Rosenberger H. , Funk M. , Madeja K. 
Published: May 2005

AbstractDer Ligandenaustausch von 1,10‐Phenanthrolin zwischen der diamagnetischen, komplexgebundenen (mitden Zentralionen: [Zn]2+, [Fe]2+, [Co]3+) und der freien Lage wird mit Hilfe der Protonenresonanzspektroskopie untersucht. Die mittleren Aufenthaltsdauern des Liganden in den Systemen mit Zn bzw. Fe als Zentralatom konnten durch eine vollständige Linienformanalyse bzw. durch Näherungsformeln bestimmt werden. Aus der Temperaturabhängigkeit der Aufenthaltsdauern wurden die Aktivierungsenergie, die freie Aktivierungsenthalpie, die Aktivierungsenthalpie und die Aktivierungsentropie bestimmt.
Critical examination of the 1H NMR spectra of aryl epoxides
Authors: Lazzeretti P. , Moretti I. , Taddei F. , Torre G. 
Published: May 2005

AbstractThe proton chemical shift of several derivatives of styrene oxides have been obtained in different solvents in order to check the relative importance of different contributions to the shielding of oxirane protons. It seems likely that ‘ring current’ and electrostatic effects can explain differences within the several compounds examined. An investigation of the conformational requirements of the phenyl group in these systems shows that the preferred conformation present in styrene oxide is also likely to be maintained in other compounds, where groups cis and trans to the phenyl ring are present. A discussion of the possibility of employing ‘ring currents,’ obtained both in the Johnson and Bovey scheme and with an SCF treatment for conformational analysis is given and it seems that this contribution, when considered alone, can only give very approximate information regarding the geometrical pattern of the molecule.
Substituent effect on the 1H NMR Spectra of trans aryl methyl oxiranes and arylpropenes
Authors: Benassi R. , Lazzeretti P. , Moretti I. , Taddei F. , Torre G. 
Published: May 2005

AbstractThe 1H NMR spectra of 1‐aryl‐2‐methyl oxiranes substituted in the phenyl ring and of the corresponding vinyl derivatives have been analysed. The substituent effect on oxiran protons seems mostly polar in character, as shown by correlations with substituent constants, solvent effects and the fact that perturbation decreases with increasing distance from the substituent. The comparison with the corresponding vinyl derivatives, in which conjugation effects are present, confirms this point. The results also seem to exclude the possibility of substituents causing significant changes on the preferred conformation of the phenyl ring. Ring current contributions on oxirane protons, evaluated by SCF procedure, show that their change with substituents is very small and does not represent a significant part of the change of proton chemical shift with substituents.
Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—XXIV: The stereochemistry of octahydroimidazo [1,5‐a] pyridine and of some N‐acetyloctahydroimidazo [1,5‐a] pyridines
Authors: Crabb T. A. , Chivers P. J. , Newton R. F. 
Published: May 2005

AbstractOctahydroimidazo[1,5‐a]pyridine is shown to preferentially adopt the trans‐fused ring conformation in solution at room temperature. The NMR spectra of the rotational isomers of some N‐acetyloctahydroimidazo[1,5‐a]pyridines and N‐acetyloctahydro‐1H‐pyrido[1,2‐c]pyrimidine are described, and the stereochemistry about the N‐acetyl bonds and the cis or trans nature of the ring fusion defined.
Transmission of long‐range coupling through three‐membered rings: The cyclopropylcarbinyl σ‐π coupling
Authors: Lambert Joseph B. , Magyar Elaine Stedman 
Published: May 2005

AbstractSpin information should be passed most effectively from a carbon‐hydrogen bond to the p‐rich carbon‐carbon bond of an adjacent cyclopropane ring when the two bonds are parallel. The existence of such a mechanism is tested in a series of spiro hydrocarbons and epoxides in which four‐bond zigzag (W) couplings are absent. The structure is varied from the ideal parallel‐orbital geometry of spirohexane and the homologous epoxide to the unfavorable staggered‐orbital geometry of spiro[2·5]octane and its epoxide. In the parallel‐orbital situation, a four‐bond non‐W coupling of about 0·2 Hz is found; this coupling is absent in the other geometric situations. The meager ability of the cyclopropyl bonds to pass spin information, when compared to the π‐orbitals in alkenes, is discussed in terms of the electronic structure of cyclopropanes.
Determination of the optical purity of some substituted N‐phenylpropionamides by NMR spectroscopy
Authors: Snatzke Günther , Fox John E. , El‐Abadelah Mustafa M. 
Published: May 2005

AbstractThe NMR spectra of a series of chiral propionamides have been determined in D(+)1‐phenylethylamine solution. The α‐methine protons of the propionic acid moiety in the propionamide enantiomers were found to be anisochronous in this solvent. The sense of non‐equivalence of these protons was found to be the same for all members of a homochiral series. The chemical shift difference between their signals was demonstrated to be dependent upon the temperature and concentration of the solution. A method is described whereby the enantiomeric purity of the amides could be calculated from these signals in cases where the position of the baseline in their spectra was unknown.
Phosphorus–nitrogen rotation barriers: Further studies
Authors: Distefano S. , Goldwhite H. , Mazzola E. 
Published: May 2005

AbstractPhosphorus–nitrogen rotation barriers have been determined by low temperature NMR methods in a variety of compounds of the type RP(X)NR2′. The observed activation parameters are concentration and solvent independent. Increasing the bulk of substituents on nitrogen increases the barrier. Phosphonamidous fluorides (X = F) have lower barriers than the corresponding chlorides (X = Cl). Increasing the bulk of substituents on phosphorus decreases the barrier.
Nuclear magnetic resonance studies of internal rotation: IV—rotational barriers and conformation of phthalic amides
Authors: Spassov S. L. , Dimitrov V. S. , Kantschovska I. 
Published: May 2005

AbstractThe rotational barriers about the CN bond of the N,N,N′,N′‐tetramethyldiamides of phthalic, isophthalic and terephthalic acids have been determined by the iterative total line shape NMR method. Some evidence about the conformation of these compounds in solution has also been obtained by infrared and dipole moment studies.
Phosphates d'énols: XI—Etude des constantes de couplage 3J(POCH) et 4J(POCCH)
Authors: Gaydou Emile M. , Llinas Jean Richard 
Published: May 2005

AbstractL'analyse RMN des phosphates d'énols E et Z non substitués sur le carbone 1, nous a permis de mettre en évidence l'existence de conformations planes et gauches. Dans le cas de phosphates ne comportant pas de groupement volumineux en position cisoïde par rapport au groupement phosphate, il est possible d'envisager deux formes planes et deux formes gauches. La conformation la plus stable est la forme plane où le groupement phosphate est en trans par rapport à la double liaison. Dans le cas de phosphates comportant un groupement volumineux en position cisoïde, la forme plane où le groupement est en cis par rapport à la double liaison n'a pu être mise en évidence. Un bon accord est obtenu entre les valeurs des angles dièdres des formes gauches déterminées à partir des constantes de couplage et calculées en utilisant la méthode CNDO/2. La variation des constantes 4J(POCCH) cisoïde et transoïde en fonction de la température, a pu être justifiée et permettra d'expliquer le renversement apparent de la valeur de ces constantes lorsque l'on place un substituant sur le carbone 158.
Stéréochimie en série aziridine: VI—Etude en Résonance Magnétique Nucléaire d'alcools aziridiniques primaires (configuration à l'azote, isoméries de rotation)
Authors: Baret Paul , Handel Henri , Pierre Jean‐Louis 
Published: May 2005

AbstractSix alcools primaires aziridiniques diversement substitués sont étudiés en résonance magnétique nucléaire, à différentes températures. La configuration à l'azote est établie; lorsque l'inversion est effectivement observée, les paramètres cinétiques associés au phénomène sont déterminés. L'isomérie de rotation autour de la liaison cycle‐carbone porteur de l'hydroxyle est étudiée à partir des deux constantes de couplage vicinales correspondant aux deux protons diastéréotopiques du groupement hydroxyméthyle. La rotation de l'hydroxyle est également abordée au moyen du couplage J(HOCH) déterminé dans CCl4 pour certains termes. Une description globale des conformations peut être alors établie.
N‐Methyl chemical shifts in some 2‐, 3‐ and 4‐substituted N‐methylpyridinium salts
Authors: Deady L. W. , Willett G. D. 
Published: May 2005

AbstractThe chemical shifts of the N‐methyl group in a series of 2‐, 3‐ and 4‐substituted N‐methylpyridinium salts have been measured in DMSO solution. The shift is primarily affected by resonance interaction between the substituent and aza group, and the results suggest that the resonance effect from a 2‐substituent is at least as great as from the corresponding 4‐substituent.