bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of stereochemistry on hydroxyl proton chemical shifts and coupling constants in carbohydrates
Authors: Adams Bruce , Lerner Laura E.
Published: May 2005

Chemical shifts and coupling constants of hydroxyl protons for a series of simple carbohydrates are reported and several trends extracted: (1) chemical shifts are relatively independent of the experimental conditions if referenced to water; (2) chemical shifts are sensitive to the orientation of the HO group and its neighbors; and (3) coupling constants fall within a relatively narrow range, which is indicative of rotational averaging. These observations suggest that NMR parameters of hydroxyl protons can provide important diagnostic information about the stereochemistry of simple carbohydrates and may prove useful for analysis of more complex compounds.
Pseudo‐triple‐resonance BIS‐HMQC experiment for the 1H‐detected measurement of couplings between rare spins
Authors: Kupče Ēriks , Lukevics Edmunds , Wrackmeyer Bernd
Published: May 2005

Improvement in the sensitivity and accuracy of the 1H‐detected experiment for measurement of coupling constants between rare spin‐1/2 nuclei X and Y is achieved if a bi‐selective (BIS) pulse is used to excite selectively protons coupled to Y, prior to the standard 1HX HMQC experiment (BIS‐HMQC). In the 2D spectrum even very small coupling constants J(X, Y) can be measured and the signs of J(X, Y) and J(Y 1H) can be compared. High‐quality 2D spectra were obtained using post‐acquisition binomial filters. The 1H13C29Si spin systems of the methoxy group in p‐trimethoxysilyltoluene [2J(29SiO13C) = 1.3 Hz] and of the diethylamino group in bis(diethylamino)dimethylsilane [2J(29SiN13C) = 2.5 Hz] serve for demonstrating the techniques.
Irradiated nifedipine—a nitroso spin trap
Authors: Staško Andrej , Mišík Vladimir , Omelka Ladislav
Published: May 2005

Irradiation of nifedipine yields a new nitroso spin trap which traps carbon‐centred radicals and also forms relatively stable alkoxyl radical adducts. In addition, the reaction with unsaturated lipids yield highly stable covalent nitroxide radicals.
Deuterium and 18O isotope effects on 13C chemical shifts of sterically hindered and/or intramolecularly hydrogen‐bonded o‐hydroxy acyl aromatics
Authors: Hansen Poul Erik , Ibsen Solveig N. , Kristensen Tina , Bolvig Simon
Published: May 2005

A series of sterically hindered o‐hydroxy aromatic ketones were synthesized, including benzene, naphthalene, phenanthrene and pyrene derivatives. Deuterium isotope effects on the 13C chemical shifts of 2‐hydroxy‐1‐acenaphthone and other sterically hindered, intramolcularly hydrogen‐bonded aromatic ketones (OH exchanged) are shown to be unusual. The two‐bond isotope effects are very large. Likewise are the istope effects on CO, C1, C3 and C4 carbon resonances and some show unusual signs. These unusual effects are explained by a higher degree of twist in the deuterio than the protio compound. Steric isotope effects are also observed on OH chemical shifts of sterically hindered o‐hydroxy acetyl aromatic compounds deuteriated at the methyl group. These isotope effects show non‐additivity. For one‐bond isotope effects, 1Δ13C(18O), hydrogen bonding leads to a decrease, whereas twisting of the carbonyl group leads to an increase. Two hydrogen bonds to the same acceptor has a reduced cumulative effect. Data for sterically hindered, hydrogen‐bonded compounds are found to fall outside the correlation between δ(17O) and 1Δ13C(18O).
Proton assignment and structural features of a peptide from the chymosin‐sensitive region of bovine k‐casein determined by 2D‐NMR spectroscopy
Authors: Plowman Jeffrey E. , Smith Mark H. , Creamer Lawrence K. , Liddell Michael J. , Coddington Jan M. , Gibson Jennifer J. , Engelbretsen Darren R.
Published: May 2005

The peptide k‐casein(98–111) corresponding to the sequence 98–111 of bovine k‐casein (His‐Pro‐His‐Pro‐His‐Leu‐Ser‐Phe‐Met‐Ala‐Ile‐Pro‐Pro‐Lys), which includes the aspartic protease sensitive region, was analysed by 2D 1H NMR spectroscopic techniques in DMSO‐d6. The spectral peaks of all protons resolved at 400 MHz were assigned. The changes in the amide proton shifts with pH and temperature and the existence of particular cross peaks in the ROESY spectra were consistent with the central region of the peptide being in an extended chain in solution but with some type of distinct conformations at the N‐ and C‐termini. The results are not consistent with the peptide having any helical structure at either low or high pH.
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

Ten 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

The 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.
Analysis of the 1H NMR spectra of some diethyl phosphonates
Authors: Byrne Lindsay T. , Ferro Vito , Stevenson Sandra , Stick Robert V.
Published: May 2005

A series of nine diethyl phosphonates were prepared and an analysis of their 1H NMR spectra was undertaken. Some erroneous literature assignments of signals were revised.
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

13C 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

The 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

High‐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

The 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

Over 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

A 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

Natural 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

Complete 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

The 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

31P 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

The 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

Der 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

The 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

The 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

Octahydroimidazo[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

Spin 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

The 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

Phosphorus–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

The 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

L'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

Six 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

The 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.
Conformations of highly hindered aryl ethers: XXIII–PMR evidence for preferred conformations and intramolecular π complex formation in nitrophenyl naphthyl ethers
Authors: Lehmann F. Pedro A.
Published: May 2005

The PMR spectrum of 2‐bromo‐4,6‐dinitrophenyl 2′‐naphthyl ether (1) is consistent with the preferential adoption of a twist conformation (1a) in which the 6‐nitro group and the 1′‐hydrogen are located endo to the ether link. This preference is explained by the formation of an intramolecular π complex between the 6‐nitro group and the C1′C2′ bond, which is stronger than that formed with the C2′C3′ bond, in accord with their bond orders. This study adduces further evidence in favor of: (a) the adoption of twist conformations by these and related ethers, (b) the importance of intramolecular π complex formation as a conformational influence, (c) the formation of complexes in such cases is with specific portions of, and not the complete, π cloud and (d) indicates that similar effects may be discerned in analogous ethers related to the thyroid hormones.
Kernresonanzspektroskopische Untersuchungen an Pentafluorphenylsubstituierten Silanen: II–Fernkopplungen und Through Space Effekte
Authors: Hägele Gerhard , Weidenbruch Manfred
Published: May 2005

Longrange‐Kopplungen des Typs 5J(FH) und 6J(FH) werden bei Silanen des Typs (C6F5)nSiR4‐n (n = 1, 2, 3; R = Alkyl, Aryl) sowie den Disilanen C6F5[Si(CH3)2]2R (R = CH3, C6F5) beobachtet. Eine typische Linienverbreiterung der Fluor‐resonanzspektren von (C6F5)nSiR4‐n (n ≧ 2) wird auf Spinsysteme des Typs ([AC]2B)n bzw. ([AX]2M)n mit interanularen Kopplungen der ortho‐Fluor‐atome benachbarter Ringe zurückgeführt.
Zur NMR–Spektroskopie der meso‐ und racem‐Formen einiger Verbindungen mit zwei gleichwertigen asymmetrischen Kohlenstoffatomen in einer offenen Kette
Authors: Larsson Erik
Published: May 2005

Die chemischen Verschiebungen der CH‐ und (OCH3)‐Protonen der folgenden in meso‐ und racem‐Formen vorkommenden Verbindungen wurden in verschiedenen Lösungsmitteln bestimmt: in (CD3)2CO; (RCHCO2H)2 (R = Cl, Br, C6H5S, CH3COS), (C6H5CHCO2H)2S und (C6H5CHCO2H)2S2; in (CD3)2CO, CDCl3, CCl4, C6D6, CS2; (RCHCO2CH3)2 (R = Cl, Br, C6H5, C6H5S, CH3COS), (C6H5CHCO2CH3)2S und (C6H5CHCO2CH3)2S2. Es wurde gezeigt, dass die chemische Verschiebung eines Protons in der meso‐Form derjenigen in der racem‐Form sein kann und dass die Differenzen zwischen ihnen nicht zu einer relativen Konfigurationsbestimmung verwendet werden können. Der Unterschied in den NMR‐Spektren einer meso‐ und einer racem‐Form ist in den meisten Fällen hinreichend gross, um eine Bestimmung der beiden Formen in einem Gemisch derselben zu ermöglichen.
Ultra long range 19F19F spin–spin coupling
Authors: Mitchell Peter J. , Phillips Lawrence , Roberts Stephen J. , Wray Victor
Published: May 2005

The observation of long range (10–14 bond) spin–spin coupling between fluorine nuclei (which are very far apart in space) is used to provide information about electronic interactions in bridged dinuclear aromatic compounds.
Résonance Magnétique Nucléaire en phase nématique. Exploration de la barrière d'empêchement à la libre rotation pour le fluorure d'acroyle et l'acroléine
Authors: Courtieu J. , Gounelle Y. , Gonord P. , Kan S. K.
Published: May 2005

Les spectres RMN de l'acroléine et du fluorure d'acroyle (CH2CHCOX avec XH et F) orientés dans une phase nématique ont été interprétés et des informations sur l'équilibre conformationnel s‐cis ⇄ s‐trans ont été obtenues. La barrière s'opposant à la libre rotation du groupement COX a été étudiée à l'aide de différentes hypothèses. Un bon accord a été obtenu entre les spectres expérimentaux et les spectres calculés en utilisant une fonction potentiel V(ϕ) = ΣnVn(1 – cos nϕ)/2, avec V1 = −200 cal mol−1, V2 = 1500 cal mol−1 et V3 = 400 cal mol−1 pour le composé fluoré; et V1 = 1200 cal mol−1, V2 = 3000 cal mol−1 et V3 = 2000 cal mol−1 pour l'acroléine; ce dernier composé existe presque exclusivement sous la forme s‐trans.
Etude conformationnelle de la dimethyl‐3,4 cyclopentanone trans: II—Spectres de RMN
Authors: Sablayrolles Claire , Granger Robert , Girard Jean‐Pierre , Bodot Hubert , Aycard Jean‐Pierre , Bardet Lucette
Published: May 2005

Les spectres RMN de la diméthyl‐3,4 cyclopentanone trans et de la diméthyl‐3,4 tétradeutério 2,2,5,5 cyclopentanone‐trans ont été analysés. Les constantes de couplage, déterminées pour le composé deutérié, sont en faveur d'une conformation diéquatoriale des groupements méthyle.
Internal rotation around the isopropyl‐nitrogen bond and stable conformations of S‐methyl‐N,N‐di‐isopropyldithiocarbamate, dichlorotin(IV) bis(N,N‐di‐isopropyldithiocarbamate) and related compounds
Authors: Tanaka Toshio , Watanabe Noriyoshi
Published: May 2005

Temperature dependent proton magnetic resonance spectra of dichloro‐ and dimethyltin(IV) bis(N,N‐di‐isopropyl‐dithiocarbamate) (1 and 2, respectively), dimethylchlorotin(IV) N,N‐di‐isopropyldithiocarbamate (3), dimethyltin(IV) bis(N‐isopropyldithiocarbamate) (4), S‐methyl‐N,N‐di‐isopropyldithiocarbamate (5) and S‐methyl‐N‐isopropyldithiocarbamate (6) were measured in halogenated hydrocarbons or CS2. The internal rotation around the isopropyl–nitrogen bond of 1, 2, 3 and 5 is restricted below −30°C, and that of 4 and 6 below −70°C; 1, 2 and 3 exist as only one conformer in dichloromethane, while 5 exists as two rotational isomers with respect to the isopropyl–nitrogen bond with a mole ratio of about 2·7:1·0 in CS2 below −30°C. At this temperature, 6 exists as two stereoisomers in CS2 with a mole ratio of about 1·2:1·0, although there is no stereoisomer in 4. From these results, possible conformations of the compounds at low temperature are proposed and the assignments of each proton signal are described.
Sur le calcul a priori des déplacements chimiques de 1H et de 19F
Authors: Stahl‐Larivière H.
Published: May 2005

Nous proposons une nouvelle méthode de calcul du déplacement chimique de 1H et de 19F dans les molécules organiques saturées. Les résultats obtenus montrent que celui‐ci est le bilan de plusieurs contributions et permettent une évaluation de celles‐ci: une contribution diamagnétique d(—ϵ) proportionnelle à la charge nette ϵ de l'environnement électronique du noyau étudié et des contributions paramagnétiques pX de chacun des substituants géminés, constantes pour chaque substituant X lorsqu'on passe d'une molécule à une autre. Pour les deux noyaux, les valeurs de d utilisées sont déduites des calculs théoriques de l'écran dans l'atome libre. Cette méthode, qui n'utilise qu'un nombre très restreint de paramètres déduits de l'expérience nous a permis de retrouver les déplacements chimiques expérimentaux avec un écart moyen, pour 1H de ± 0,32 ppm, pour 19F de ± 11 ppm. Elle a donc l'interêt de fournir une relation quantitative simple entre déplacement chimique et structure permettant de dégager des indications précises sur l'origine des contributions des environnements voisins.
Long range carbon–proton coupling constants in pyridine
Authors: Miyajima Goh , Takahashi Kensuke , Sugiyama Hiroshi
Published: May 2005

Carbon‐13 NMR spectra of pyridine have been observed by using the slow scan technique in the absorption mode. The long range coupling constants between carbon‐13 and protons have been obtained and assigned by the isotope substitution method.
Analyse isotopique de mélanges d'éthanols deutériés C2H5‐nDnOH
Authors: Bengsch E. , Corval M. , Martin G. L.
Published: May 2005

On décrit l'analyse isotopique qualitative et quantitative de mélanges d'isomères nucléaires de l'éthanol C2H5‐nDnOH, obtenus par diverses réactions de réduction et dans lesquels une des variétés domine nettement. Après détermination par spectrométrie de masse du pourcentage des variétés isotopiques de même deutériation globale, celles‐ci sont identifiées par RMN protonique et deutonique en combinant les schémas spectraux de tous les isomères qui peuvent être envisagés jusqu'à concordance avec les spectres expérimentaux; on tient compte de l'effet isotopique sur δ. Les variétés isotopiques présentes sont ensuite dosées avec une précision variable par intégration de raies caractéristiques. On compare également pour chaque mélange les intensités globales des signaux méthyliques et méthyléniques en résonance du proton et du deuton. Pour les signaux méthyléniques, élargis par relaxation quadrupolaire du deuton, on fait apparaître les structures fines en augmentant la température de l'échantillon.
Proton spin coupling constants in cycloalkenes
Authors: Solkan V. N. , Sergeyev N. M.
Published: May 2005

The proton‐proton coupling constants in cyclopentadiene, cyclohexadiene, cycloheptatriene, cyclooctatetraene, cyclopentene and cyclohexene have been calculated using the finite perturbation INDO method. The carbon geometry was taken from the corresponding electron diffraction studies. The theory gives satisfactory agreement with experiment. In terms of the many factor structural model, distance and angle distortions have been studied in ethylene, cis‐1,3‐butadiene and cis‐2‐butene. It has been established that these distortions produce noticeable changes only for those protons whose co‐ordinates are changed. The coupling constants across three, four and five bonds are discussed separately in connection with the structural factors and the σ–π contribution. Finally, variations in the proton co‐ordinates in cyclopentadiene are used to optimize the proton couplings.
Stereochemical studies: XVII—the proton coupling constants and conformational equilibria of trans‐1,2‐disubstituted cyclohexenes
Authors: Viktorova N. M. , Knyazev S. P. , Zefirov N. S. , Gavrilov Yu. D. , Nikolaev G. M. , Bystrov V. F.
Published: May 2005

The vicinal 3Jaa and 3Jee spin‐spin coupling constants of a number of deuterated trans‐1,2‐disubstituted cyclohexenes and the ΔH and ΔS values of the conformational equilibria of these compounds have been determined by computer optimisation of the 3J(HH) = f(T) function. Compounds with —CF3 and CCl3 substituents were shown to have an enhanced proportion of the diaxial conformer.
Etude par RMN à haut champ des monofluoroanilines
Authors: Forchioni A. , Chachaty C.
Published: May 2005

L'analyse des spectres RMN à 250 MHz des monofluoroanilines complexées par du Pr(FOD)3 a permis de déterminer avec précision les constantes de couplages J(HH) et J(FH) de ces composés. La validité des attributions a été contrôlée en reconstituant les spectres par calcul électronique.
Etudes RMN en série hétérocyclique—XIII:Spectres des azoles dans l'acide sulfurique
Authors: Elguero José , Fruchier Alain , del Carmen Pardo Maria
Published: May 2005

Les spectres RMN du benzimidazole, de l'indazole, du phényl‐1 imidazole, du phényl‐1 pyrazole et de certains de leurs dérivés méthylés, ont été étudiés dans l'acide sulfurique en vue de déterminer les couplages avec les protons portés par les azotes.
Conformational analysis of 7,7‐dichloro‐2,5‐dioxabicyclo[4.1.0] heptane by NMR
Authors: Schauble J. Herman , Lazear Nelson R.
Published: May 2005

The 1H NMR spectra of 7,7‐dichloro‐2,5‐dioxabicyclo‐[4.1.0]heptane (1) were analyzed through the application of programs NMRIT and NMREN2.

See Ref. 1.

The half‐chair conformation of 1 was obtained from the vicinal coupling constants by the Buys R method.

See Ref. 2.
Etude par RMN du proton de la complexation du triéthylaluminium par l'éther diéthylique
Authors: Marchal J. P. , Canet D. , Bonnet P. , Barriol J.
Published: May 2005

La complexation entre le triéthylaluminium et l'éther diéthylique a été étudiée par résonance magnétique du proton. On a pu observer des signaux distincts pour le triéthylaluminium libre et le triéthylaluminium lié. Une stoechiométrie 1:1 est démontrée grâce aux rapports des aires de ces signaux. A plus haute concentration d'éther, des mesures de déplacements chimiques prouvent qu'il n'apparaît pas d'autres complexes.
NMR study of the acetylation of 2,3‐diphenylbenzofuran
Authors: Barboiu V. , Wexler H. , Arventiev B.
Published: May 2005

The positions of acetyl groups introduced by Friedel‐Crafts reactions into 2,3‐diphenylbenzofuran and its derivatives monomethylated in the 5,6 and 7 positions and dimethylated in the 5,6 positions were determined by means of single and double resonance NMR spectra. It was found that the first acetyl group occupies position 6 for all 6‐unmethylated compounds and position 5 for 6‐methylated compounds. The next two acetyl groups enter the para positions (4′ and 4″) of the phenyl groups with the same probability. When positions 5 and 6 are methylated the acetyl group enters positions 7,4′ and 4″ which are found to be of almost equal reactivity. The NMR parameters of compounds studied are listed.
Rotational isomerism: XVII—solvent effects on the NMR spectra and rotamer energies of some tetrahaloethanes
Authors: Abraham R. J. , Cooper M. A. , Siverns T. M. , Swinton P. F. , Weder H. G. , Cavalli L.
Published: May 2005

The NMR spectra of 1,1‐dichloro‐2,2‐difluoroethane (1), 1,1‐dibromo‐2,2‐difluoroethane (2), meso and dl 1,2‐dichloro‐1,2‐difluoroethane (3) and 1,1,2,2‐tetrachloroethane (4) have been analysed in a number of solvents. The 19F spectrum of 3 in L‐bornyl acetate at 56·4 and 94·1 MHz allows an unambiguous identification of the meso and dl isomers. The spectra of the d and l isomers consist of two AA′XX′ spectra with a small chemical shift difference between the d and l forms, whilst that of the meso form is an apparent AA′XX′ spectrum at 56·4 MHz but an ABXX′ spectrum at 94·1 MHz, the 19F nuclei in this isomer being anisochronous in this solvent. The observed solvent and temperature dependence of the couplings of 1, 2, meso 3 and 4 when combined with the calculated solvation energies, allow the determination of the rotamer energies and couplings in these molecules. The rotamer energy differences (Eg – Et) in the liquid and vapour states are 0·6 and −0·2 kcal/mol (1); 0·4 and −0·5 kcal/mol (2); 0·9 and 0·2 kcal/mol meso (3) and −0·1 and −0·8 kcal/mol (4). The 3J(HH), 3J(HF) and 3J(FF) couplings for the distinct rotamers are considered together with those of similarly constituted molecules. The general agreement demonstrates that the solvation theory may be applied to multisubstituted ethanes without any basic modifications. The trans oriented HH couplings show a linear substituent electronegativity dependence, which differs appreciably from that obtained for disubstituted ethanes, however. The gauche couplings show the influence of dihedral angle variations as well as substituent electronegativity. The rotamer 3J(FF) couplings in meso 3 are −38·2 Hz (Jt) and −17·4 Hz (Jg).
Carbon‐13 magnetic resonance study of spiro compounds
Authors: Zimmermann D. , Ottinger R. , Reisse J. , Christol H. , Brugidou J.
Published: May 2005

A large series of cyclohexane and cyclopentane spiro compounds has been studied by carbon‐13 NMR. Increments have been derived in terms of α, β, γ spiro substituent effects, one ring being considered as the substituent of the other. As usual α and β effects are paramagnetic and γ effects are diamagnetic. They are compared with the corresponding effects associated with the introduction of a gem dimethyl group into a cyclohexane or cyclopentane ring. The size of the two rings involved in the spirane structure has a marked influence especially on the chemical shift of the spirane carbon atom. Comparison between monospiro and dispiro derivatives gives information about the so‐called 1,5 or δ effect which is paramagnetic. From an analytical point of view, carbon‐13 NMR appears to be a powerful method of detecting the spirane structure, apparently including the relative size of the rings.
1H NMR study of cyclo‐L‐Thr‐L‐Thr and cyclo‐L‐Thr‐L‐His conformations
Authors: Ptak Marius , Heitz Annie
Published: May 2005

Cyclodipeptides containing L‐Thr and L‐His residues have been studied by 1H NMR in D2O and DMSO‐d6. In the neutral form in D2O as in DMSO‐d6, the folded form of the L‐His residue is not unique. The diketopiperazine ring seems to be not strictly planar.
Boron–carbon coupling constants: II—the tetraphenylborate anion
Authors: Odom Jerome D. , Hall Laurence W. , Ellis Paul D.
Published: May 2005

Boron‐carbon coupling constants were obtained from the 13C FT‐NMR, 1H noise decoupled spectra of sodium tetraphenylboron and tetra‐n‐butylammonium tetraphenylboron. The appearance of the spectra, as well as values obtained for J(BC), are discussed and contrasted with previously published data.
Chemical shift reagents in the study of polycyclic alcohols IX—1H NMR spectra of myrtenol and some other primary alcohols
Authors: Paasivirta Jaakko , Häkli Harri , Widen Karl‐Gustav
Published: May 2005

Structure proof of (—)‐myrtenol, 3‐cyclopentenyl‐1‐methanol and 5‐norbornene‐2‐endo‐methanol has been obtained from their proton magnetic resonance spectra in carbon tetrachloride containing different added amounts of tris(dipivaloylmethanato)europium. For each alcohol, a 1:1 complex structure with Eu(dpm)3 could be computed, in which the calculated pseudocontact shift effects on all skeleton protons of the ring system were consistent with the observed shift effect values. A considerable contact contribution of opposite sign to that of the pseudocontact part of the effect could be estimated for the methylene protons of the CH2OH group.
Quantitative 13C NMR analysis of mixtures of 2,4‐di‐isocyanatotoluene and 2,6‐di‐isocyanatotoluene
Authors: O'Neill I. K. , Pringuer M. A.
Published: May 2005

Some isomeric mixtures, such as the toluene di‐iso‐cyanates, may be quantitatively analysed by measurement of peak heights of a 13C FT‐NMR spectrum without the use of gated decoupling or the addition of paramagnetics.
1H NMR spectra and electronic structure of 3‐arylmethyl‐idenephthalide and 3‐arylthiomethylidenephthalide derivatives
Authors: Vida M. , Kellö V. , Liptaj T. , Perjéssy A. , Hrnčiar P. , Lácová M.
Published: May 2005

The 1H NMR spectra of trans‐3‐phenylmethylidenephthalide and trans‐3‐phenylthiomethylidenephthalide derivatives were investigated. After applying a correction for the anisotropy of substituents and/or for changes of ring current in the substituted aromatic ring, linear correlations were obtained between the chemical shifts of protons of the substituted phenyl group and the methine group and s̀ constants of substituents. The influence of the bridge heteroatom on the transfer of electronic effects of substituents through the molecules under study is discussed.
Konformationsanalyse von 1,4:3,6‐bis(Thioanhydro)‐D‐idit Derivaten
Authors: Sohár P. , Kuszmann J.
Published: May 2005

Die dominierende Konformation einiger 1,4:3,6‐bis(Thioanhydro)‐D‐idit Derivate (1a bis 1c) wurde durch 1H NMR Untersuchungen bestimmt. Weiterhin konnte auch die Konfiguration und Konformation des durch Oxydation aus 2,5‐Di‐O‐acetyl‐1,4:3,6‐bis(thioanhydro)‐D‐idit (1b) hergestellten symmetrischen (3) und asymmetrischen (4) Disulfoxyds, sowohl die des Disulfons (5) aufgeklärt werden.
Etude RMN de β‐hydroxy‐phosphonates‐esters. Détermination du signe du couplage stéréospécifique 4J(PCCOH) dans le diastéréoisomère RS,RS
Authors: Bottin‐Strzalko T. , Pouet M. J. , Simonnin M. P.
Published: May 2005

Des expériences d'INDOR effectuées sur le β‐hydroxyphosphonate ester RS,RS en solution dans le (CD3)2CO ou (CD3)2SO montrent que le couplage 4J(PCCOH) est positif. La valeur plus élevée de ce couplage dans (CD3)2SO que dans (CD3)2CO indique qu'une géométrie en W rend le couplage plus positif.
Dual standard addition for quantitative NMR analysis
Authors: Cockerill A. F. , Harden R. C. , Davies G. L. O. , Rackham D. M.
Published: May 2005

A technique is described for quantitative NMR measurement which involves the use of a pair of internal standards. This procedure overcomes several of the problems encountered with only one standard material. A computer programme is described for statistical treatment of the results.
Carbon‐13 NMR of some representative reactive small ring nitrogen heterocycles
Authors: Nair V.
Published: May 2005

The PFT 13C NMR spectra of some representative 1‐azirines are discussed. Two striking features are the large 13C1H spin coupling constants and the diagnostic chemical shift of C3.