bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation by dynamic NMR spectroscopy of the mechanism of rotation about the carbondouble bond in nitroenamines
Authors: Bakhmutov V. I. , Burmistrov V. A.
Published: May 2005

Rapid Z,E‐isomerization of nitroenamines RNHCHC(NO2)COOCH3 in solutions was investigated by dynamic NMR spectroscopy. In weakly basic solvents all the studied nitroenamines isomerize by a thermal mechanism. In pyridine the isomerization proceeds by the thermal mechanism in aliphatic enamines with RCH3, COCH3 and H, but involves the formation of an intermediate mesomeric ion with kinetically controlled ionization of the NH bond in the case of aromatic nitroenamines where R = X—Ph‐.
Synthesis of new crown ethers and their metal complexes: 1H and 13C NMR study
Authors: Torizuka Koichi , Sato Takeo
Published: May 2005

A new type of crown ethers containing a diphenyl ether unit has been prepared, the ring size ranging from 12 to 36. 1H and 13C NMR spectra of both free ligands and their metal‐ion complexes have been recorded. For 18‐ and 21‐membered compounds a general downfield shift was observed for both methylene and aromatic proton resonances on metal‐ion complexation. The stoichiometry of K+ and Na+ complexes was deduced from chemical shift dependence on metal‐ion concentration. The K+ and Na+ complexes of 18‐ and 21‐membered rings have a guest to host ratio of 1:1, whereas the K+ salt of the 15‐membered ring exists as a 1:2 complex in solution. The 1H shift observed on salt formation was attributed to electric‐field and conformational effects. The 13C resonances for the aryl carbons, C‐1, C‐2 and C‐3, and the α‐methylene carbon in 15‐ and 18‐membered rings were shifted upfield when an equivalent amount of KSCN was added in CDCI3−DMSO‐d6. The shift changes were independent of the anion, and similar results were obtained for SCN−, Br−, and I− salts. The upfield shift is explained by conformational factors. The spectral changes were slight for 12‐ and 36‐membered rings. In 15‐ and 18‐membered rings, complexation induces conformational changes which force the C‐α carbon into the plane of the benzene ring. The solution conformation of these molecules is discussed.
Psi‐angle dependence of geminal proton–carbonyl‐13C coupling constants in peptides. A theoretical investigation
Authors: Mohanakrishnan P. , Easwaran K. R. K.
Published: May 2005

Theoretical calculations of the geminal carbonyl‐13C‐ proton coupling constant, 2J(C′H), in α‐amino acids have been carried out using Dirac Vector model and Penney‐Dirac bond order formulations. The results indicate that the couplings are dependent on the backbone torsion angle psi (ψ) of the amino acid residues in peptides. The meagre available experimental data seem to support the theoretical findings.
IR, 1H NMR and 13C NMR spectra of isomeric 1‐aryl‐4‐methyl‐3‐ and‐5‐pyrazolecarboxylic esters
Authors: Sohár Pál , Fehér Ödön , Tihanyi Endre
Published: May 2005

The IR, 1H and 13C NMR spectra of six esters of 1‐aryl‐4‐methyl‐3‐ and 5‐pyrazolecarboxylic acids are reported. On the basis of their spectra the 3‐ or 5‐position of the substituent in such structural isomeric pairs can be established without recourse to the spectrum of the other member of the pair. The spectral data also give information on the conformation, which depends on the relative position and size of the hetero ring substituents.
Etude par RMN du 13C d'Epoxydes en Série Diterpénique
Authors: Delmond Bernard , Papillaud Bernard , Valade Jacques , Petraud Michel , Barbe Bernard
Published: May 2005

Les auteurs étudient au moyen de la RMN du 13C divers époxydes préparés à partir d'esters méthyliques dérivés d'acides résiniques diterpéniques appartenant au groupe pimarique. Cette analyse permet de dégager en fonction de la configuration du cycle époxydique, certains effets sur les déplacements chimiques des carbones en α, β, γ et δ par rapport à l'oxygène époxydique.
13C NMR of α‐haloketones
Authors: Yalpani M. , Modarai B. , Khoshdel E.
Published: May 2005

The carbon chemical shifts of several series of α‐haloketones have been measured. Whereas the carbon carrying the halogens shows a regular downfield shift with increasing electronegativity of the substituents, the adjacent carbonyl carbon is shifted upfield by chlorine, bromine and iodine, and is little affected by fluorine substitution. The conformational implications of these results are discussed.
Nitroxide biradicals from substituted bis(hydroxy‐ureas)
Authors: Everard John. E. , Parlett Graham R.
Published: May 2005

The EPR spectra of several nitroxide biradicals derived from substituted bis(hydroxy‐ureas) have been determined. The main differences in these spectra arose dur to intramolecular interaction of the nitroxide groups. Interaction was only observed for the case where the nitroxide group was bonded to an aliphatic group.
13C‐NMR‐Untersuchungen zur Azido‐Tetrazol‐Valenzisomerie. Tetrazolo[1,5‐α]pyrimidine
Authors: Könnecke Andreas , Kleinpeter Erich , Lippmann Eberhard
Published: May 2005

Die 13C‐NMR‐Spektroskopie wurde zum Studium der Azido‐Tetrazol‐Valenzisomerie von drei Tetrazolo‐[1,5‐a]pyrimidinen herangezogen. Große chemische Verschiebungsänderungen der C‐4‐Kohlenstoffatome eignen sich zur Unterscheidung von Azido‐ und Tetrazoloisomeren. Daneben wurde die Struktur neuer Heterocyclen gesichert und gezeigt, daß die Arbeit von LaNoce und Giuliani bezüglich 9‐Methyl‐s‐triazolo‐[4,3‐c]tetrazolo[1,5‐a]pyrimidin unkorrekt ist.
Lanthanide shift reagents. XII Equilibrium binding constants for aromatic aldehydes and ketones with tris‐(tetramethylheptanedionato)europium, eu(thd)3
Authors: Rackham David M.
Published: May 2005

The binding constants, K, are reported for Eu(thd)3 with 11 ketones and 7 aldehydes related to acetophenone and benzaldehyde, respectively. Variations in K are rationalised in terms of the electronic and steric requirements of the aryl ring substituents.
Détermination par RMN 1H et 13C des Couplages J(CH) et J(CC) dans des Monomères Precurseurs de Lignine: Vanilline, Férulate d'Ethyle et Alcool Coniférylique Sélectivement Enrichis en 2H et 13C
Authors: Gagnaire Didier , Nardin Robert , Robert Daniele
Published: May 2005

Quelques monoméres composés modèles de ligning ont été sélectivement enrichis en 2H et 13C: c'est le cas de la vanilline, du férulate 'éthyle, de l'alcool conigérylique et du monoéthyl ester de l'acide malonique. L'effet isotopique dû au deutérium sur les déplacement chimiques 13C dans le cas de la vanilline 2H‐formyle, la vanilline 2H‐5 et l'alcool coniférylique 2H 5, αα, a permis l'attribution non ambifüe des signatux RMN 13C des carbones aromatiques. Les valeurs absolues des constants de couplages 1,2,3 J(CC)ont été déterminées à partir des specters 13C de la vanillin 13C formyle, du férulate d'éthyle et de l'alcool coniférylique, ces deux derniers ayant les positions vinyliques C‐γ et C‐β Sélectivement marquées en 13C. Il a été possible d'observer la valeur des couplages 4 (CO, C‐4) pour la vanilline, et 4 J (C‐γ, C‐4) pour le férulate d'éthyle. La détermination des couplages 1,2,3,4 J (CH) en valeurs absolues a été réalisée sur les spectes 13C en ‘découplage séquential’ des composés non marqés. Lorsque cette technique s'est révélée inutilisable à cause d'effets du second ordre, nous avons déterminé cretaines valeurs J (CH) et leurs signes, soit en analysant le spectre 1H‐RMN à 100 MHZ des alcohols coniféryliques 13C‐γ et 13C‐β comme dans le cas de 2 J (C‐β, H‐γ), 2 J (C‐β, H‐α), 2 (C‐γ, H‐β) et 3 J (C‐γ, H‐α). soit en observant le spectre proton à 250 MHZ avec une expérience de double irradiation du gérulate d'éthyle 13C‐β dans le cas de 2 J (C‐β, H‐γ).
15N NMR spectroscopy acids: 7—solvent effects on α‐and ω‐amino
Authors: Kricheldorf Hans R.
Published: May 2005

The natural abundance 15N NMR spectra of several α‐and ω‐amino acids were measured in various protic solvents. Increasing acidity of the solvents results in an upfield shift in the case of the α‐amino acids, while ω‐amino acids are almost insensitive to solvent effects.
Three‐bond 31P31P coupling and 31P chemical shift effects in dimers of phospholium salts and phosphole oxides
Authors: Quin Louis D. , Mesch Keith A.
Published: May 2005

The chemically nonequivalent 31P nuclei of the Diels‐Alder dimers of phospholium ions and phosphole oxides are coupled through three bonds by as much as 35–45 Hz. The chemical shift for a phosphorus atom in the 2‐phospholene moiety falls in the expected range; the shift for the constricted atom bridging the 6‐membered ring is far downfield, making Δδ as much as 43.5 ppm for one phospholium ion dimer.
Long‐range nuclear spin–spin coupling between selenium‐77 and phosphorus‐31 in biphosphorus compounds
Authors: Colquhoun Ian J. , McFarlane H. Christina E. , McFarlane William , Nash John A. , Keat Rodney , Rycroft David S. , Thompson David G.
Published: May 2005

The coupling constants nJ(77Se31P), n = 1–4, have been measured in the proton‐decoupled 31P NMR spectra of a range of diphosphorus selenides and diselenides. 31P–{1H, 31P} and 31P–{1H, 77Se} triple resonance experiments have been used to establish the signs of the coupling constants, and it is found that both the magnitudes and signs depend upon the stereochemical relationship of the coupled nuclei.
Déplacements Chimiques induits en RMN par un Réactif Lanthanidique: II—Analyse Conformationnelle de Sulfinamates Cycliques: Oxo‐2 Oxathiazannes‐1,2,3 et Oxo‐2 Benzo‐5,6 Dihydro‐3,4 Oxathiazines‐1,2,3
Authors: Tisnès P. , Maroni P. , Cazaux L.
Published: May 2005

Un réexamen des résultats récents de la littérature concernant les tert‐butyl‐5‐c oxo‐2‐r dioxaphosphorinanes‐1,3,2 substitués en 2 et le diméthyl‐3,3 oxo‐1 thietanne nous a conduit à choisir, dans les conditions indiquées, le modèle statique d'étude des déplacements induits par le lanthanides (DIL), plus souple d'emploi que le modéle dynamique. Son application à dix‐sept sulfinamates cycliques appartenant à deux séries, les oxo‐2 oxathiazannes‐1,2,3 (I) et les oxo‐2 benzo‐5,6 dihydro‐3,4 oxathiazines‐1,2,3 (II) confirme en présence d'Eu(fod)3, les structures établies en son absence sur les seules bases des déplacements chimiques et des constantes de couplage, et montre leur diversité conformationnelle. Pour la série I, on trouve (i) des chaises standard à SO axial (CA) lorsque la molécule ne comporte pas de substituants en position 4 et 6 ou lorsqu'ils sont équatoriaux, à une exception près; les substituants sur l'atome d'azote RMe, iPr ou tBu sont de préférence axiaux; (ii) des chaises déformées à SO et Me‐4 axiaux (CA); cette conformation permet à RPh une certaine conjugaison et à RMe ou tBu d'occuper la position axiale; (iii) des conformations croisées d'axe‐1,4 à SO axial (COA) pour les deux di‐tert‐butyl‐4‐c‐6‐c, et ‐4‐t‐6‐c phenyl‐3 oxo‐2‐r oxathiazannes‐1,2,3; (iv) la conformation croisée d'axe‐3,6 à SO axial (CNA) pour le méthyl‐4 tert‐butyl‐3 oxo‐2 oxathiazanne‐1,2,3 trans en raison de l'interaction‐1,2 Me‐4‐ ‐tBu‐3. Pour la série II, on retient des formes demi‐chaises à SO axial.
Carbon‐13 nuclear magnetic resonance spectroscopy of conjugated polyynes
Authors: Bohlmann Ferdinand , Brehm Manfred
Published: May 2005

The 13C NMR spectra of several conjugated polyyne‐aldehydes and ketones are compared with those of the corresponding alcohols. All data show considerable effects similar to those observed in conjugated polyenes.
Détermination Directe de la Stéréochimie de l'Addition de Carbènes aux Oléfines Bicycliques par RMN du Carbone‐13
Authors: Brun P. , Casanova J. , Hatem J. , Zahra J. P. , Waegell B.
Published: May 2005

Les déplacements chimiques en RMN du 13C d'une série de dérivés tricycliques obtenus par addition de carbènes sur des alcènes bicycliques sont comparés aux déplacements chimiques des oléfines de départ. La measure du déplacement chimique du carbone 7 montre que cette valeur peut être utilisée comme sonde configurationnelle pour la détermination de la stéréochimie de l'addition des carbènes étudiés.
The effects of substituents on the 5J long‐range spin‐spin coupling constants in substituted benzaldehydes
Authors: Contreras R. H. , de Kowalewski D. G. , Osella A.
Published: May 2005

Proton magnetic resonance spectra of several mono‐ and disubstituted benzaldehydes were studied using CW, INDOR and double resonance techniques. It was verified that substitution in the para position has no effect on the long‐range coupling of the aldehydic proton with the ring protons five bonds away. Substitution in the ortho and meta positions (with the exception of 2,4‐dinitrobenzaldehyde) follows closely the additivity rule effects of the substituents.
Equation de Karplus appliquée à des systèmes sp2–sp3
Authors: Jankowski K. , Bélanger J. , Söler F. , Zamojski A.
Published: May 2005

On présente une tentative d'affinage de l'équation de Karplus pour des systèmes sp2‐sp3. L'étude porte sur un total de 68 constantes de couplage vicinal venant de 32 produits différents. On obtient la meilleure équation de Karplus jusqu'à ce jour, avec un facteur d'accord relatif de 31,01%.
Tritium nuclear magnetic resonance spectroscopy. Part 11. Further consideration of referencing, isotope effects and coupling constants: Preparation of [3H]tetramethylsilane
Authors: Bloxsidge James P. , Elvidge John A. , Jones John R. , Mane Ramachandra B. , Saljoughian Manouchehr
Published: May 2005

Small discrepancies between 3H and 1H chemical shifts in organic compounds led to the finding that the ratio of Larmor frequencies ωT/ωH depends on the carbon‐hydrogen bond hybridisation. The ‘best’ ratio for ghost referencing of 3H NMR spectra was then determined from measurements on purified partially tritiated TMS as 1.066639738±2 × 10−9. Some 3H isotope effects on chemical shifts are listed and the 3H isotope effect on the methylene geminal coupling constant in benzyl methyl sulphoxide is measured. Use of 2H in the measurement of 2J(HH) coupling constants has inherent disadvantages, overcome by use of 3H substitution.
Etude RMN 13C d'un Dérivé Uniformément Enrichi en 13C. Signe des Valeurs des Constantes de Couplage Observées
Authors: Gagnaire D. , Reutenauer H. , Taravel F.
Published: May 2005

Les paramètres RMN‐13C d'un dérivé statistiquement enrichi en 13C, le 3‐O‐acétyl‐1,2:5,6‐di‐O‐isopropylidène‐α‐D‐glucofuranose utilisé comme produit d'analyse dans des expériences de biosynthèse mettant en jeu un double marquage, ont été mesurés. Des expériences de double résonance homonucléaire 13C{13C} réalisées à 62,8 MHz ont en particulier permis de déterminer les constantes de couplage 13C13C. Par calcul théorique de spectre, grâce aux effets du second ordre qui apparaissent dans les spectres réalisés à 25,2 MHz et à 15,08 MHz, le signe de ces constantes de couplage a été déterminé. La reconstitution théorique totale des spectres tient compte de la présence des isotopoméres et a été effectuée à l'aide d'un programme (dérivé d programme LAOCOON) permettant l'addition pondérée des spectres.
Carbon‐13 NMR investigation of 2,5‐diaryl‐1,4‐dithiins
Authors: Buess C. M. , Narayanan K. S. , O'Donnell D. J. , Arjunan P. , Berlin K. D.
Published: May 2005

The 13C NMR spectra of eight 2,5‐diaryl‐1,4‐dithiins were recorded and signals were assigned. A linear correlation was observed between the electronegativity of the substituent groups on C‐10,10′ and the chemical shifts of C‐10,10′ after applying corrections for the magnetic anisotropic effect of the substituents. A Hammett correlation was found between the 13C chemical shifts of C‐3,6 and C‐7,7′ and the σp+ parameter associated with the substituents on C‐10,10′. Extended electronic interaction between the π system of the aryl group and the π system of the dithiin ring was suggested by the observance of an alternating behavior in the magnitude of the substituent effects on the 13C shifts of C‐2,5 and C‐3,6. An alternating effect was also noted in the magnitude of the long‐range 13CF coupling constants for these same carbon signals in 2,5‐(10,10′‐difluoro)diphenyl‐1,4‐dithiin.
Binding dynamics in biological systems. Interaction of MOPC‐315 with 19F labelled nitrophenyl haptens
Authors: Kooistra Dale A. , Richards John H. , Smallcombe Stephen H.
Published: May 2005

We have studied the dynamics of binding of 19F labelled haptens by mouse plasmacytoma antibody MOPC‐315, a protein which shows specificity for nitrophenyl haptens. The off‐rates for the dissociation of hapten from MOPC‐315 proteins (7S, Fab′ and Fv) were determined by the application of several methods including a technique which, in certain cases, allows the direct determination of the rate of exchange of nuclei between magnetically non‐equivalent sites without requiring prior knowledge of intrinsic line widths. Used in conjunction with independently determined data on line widths, chemical shifts, and binding affinities, these studies show that the rates for hapten association to, or dissociation from, the intact 7S antibody, the Fab′ fragment, and the Fv fragment of MOPC‐315 are essentially the same. They also indicate the presence, probably in the Fv region, of a low affinity (K∼ 103 M−1) site(s) for hapten binding. The mobility of the hapten combining site decreases as the size of the protein increases. These rate data, which were determined at relatively high protein concentrations (up to 40 mg ml−1), agree with on‐rates determined at much lower protein concentrations (≤1 mg ml−1); we therefore conclude that protein aggregation, if it does occur, does not significantly affect binding in these systems.
NMR spectra, MO calculations of spin–spin coupling constants and conformational analysis of substituted 1,3‐dioxolanes
Authors: Benassi Rois , Schenetti Luisa , Taddei Ferdinando , Villa Luigi , Ferri Vincenzo
Published: May 2005

The NMR spectra of a number of 2,4‐disubstituted 1,3‐dioxolanes have been recorded and the proton chemical shifts and coupling constants derived from complete spectral analysis. Vicinal coupling constants were found to be dependent on the substituent at C‐4 and this effect is more pronounced for J(trans) of the C‐4‐C‐5 fragment. These coupling constants also indicate a homogeneous behaviour within a series with either a cis or trans configuration, although the cis behaviour differs from that of trans isomers. This has been interpreted in terms of definite ring conformations in substituted derivatives, while the unsubstituted 1,3‐dioxolane undergoes free pesudorotation. Calculations of coupling constants were performed by semi‐empirical MO methods, both for unsubstituted 1,3‐dioxolane and for C‐4 substituted derivatives in a large number of conformations, in order to compare calculated and experimental values; the correct order of J(cis) and J(trans) for 1,3‐dioxolane is obtained only by employing energies from ab‐initio MO calculations averaged over the pseudorotation circuit. For the C‐4 substituted compounds calculated coupling constants were employed in a ‘trial and error’ process for the identification of the preferred conformations of these compounds; a set of two torsional angles for each compound was derived which allows a tentative description of the geometry of each molecule. A criticism of these geometries is given according to the evidence available on the structure of substituted 1,3‐dioxolanes.
Use of 13C isotope shifts to assign carbon atoms α and β (and para) to a hydroxy group in alkyl substituted phenols and alcohols
Authors: Newmark Richard A. , Hill James R.
Published: May 2005

Doublets can be observed for carbons α and β to the hydroxyl in aliphatic alcohols containing equimolar amounts of OH and OD dissolved in (CH3)2SO containing CaSO4 desiccant. Isotopic doublets are also observed for the ipso and ortho carbons in alkyl substituted phenols. Para isotopic doublets are observable in para‐substituted phenols containing a large 2‐substituent. The isotope shift is positive (low field) for the para carbon, opposite to the negative shifts usually observed.
On the assignment of the carbon‐13 NMR spectrum of bilirubin
Authors: Kaplan Doron , Navon Gil
Published: May 2005

An individual assignment of certain peaks in the proton and 13C NMR spectra of bilirubin and of bilirubin dimethyl ester is described. The assignment was achieved through the spectra of vinylneoxanthobilirubinic acid and by off‐resonance decoupled 13C spectra of bilirubin dimethyl ester. The signals due to the endo and exo vinyl groups were separately assigned. This assignment allows a rational interpretation of previously obtained spin‐lattice relaxation times of the vinyl carbon peaks. The two vinyl groups are found to differ considerably in their motional correlation time.
Proton magnetic resonance studies of compounds with bridgehead nitrogen. 37–a comparison of the positions of conformational equilibria in 1‐methylperhydro‐oxazolo[3,4‐a]pyridines and in 1‐methylperhydrothiazolo [3,4‐a]pyridines
Authors: Crabb Trevor A. , Jupp Philip A.
Published: May 2005

cis(1‐H, 8a‐H)‐1‐Methylperhydro‐oxazolo[3,4‐a]pyridine and cis(1‐H, 8a‐H)‐1‐methylperhydrothiazolo[3,4‐a]pyridine both adopt exclusively the trans‐fused conformation in carbon tetrachloride solution at room temperature. Both parent unsubstituted systems exist under similar conditions as equilibria containing c. 67% (oxazolo compound) and 64% (thiazolo compound) of the trans‐fused conformation. In marked contrast to these similar positions of conformational equilibria in both systems the trans(1‐H,8a‐H)‐1‐methylperhydrooxazolo[3,4‐a]pyridine exists as c. 73% trans‐fused in equilibrium with a cis‐fused conformation whereas the trans(1‐H, 8a‐H)‐1‐methylperhydrothiazolo[3,4‐a]pyridine exists almost exclusively in a cis‐fused ring conformation. These differences in conformational equilibria are explained in terms of changes in non‐bonded interactions.
31P and 13C NMR study of tribenzolyphosphine (CC6H5)3 Oriented in a Liquid Crystal
Authors: Cogne A. , Wiesenfeld L. , Robert J. B. , Tyka R.
Published: May 2005

The 13C and 31P NMR spectra of the triply 13C labelled tribenzoylphosphine [] oriented in a nematic phase have been recorded. From the spectral analysis one obtains the average CPC valence bond angle value (95.9°± 0.2), and the phosphorus chemical shift anisotropy Δσ(σ∥︁ – σ ⊥) which is equal to 75 ± 15 ppm.
Proton magnetic resonance study of rotational isomerism in vinylcycloalkanes
Authors: De Maré George R. , Lapaille Serge
Published: May 2005

The vicinal coupling constant, J(12), between the vinyl CH and the ring CH protons in vinylcyclohexane was calculated from a ‘partial molecule’ six‐spin system. The 100 and 270 MHz results are in good agreement; those at 60 MHz were, however, still inaccurate in this approximation. J(12) increases with increasing solvent polarity and decreasing temperature. The energy difference between the s‐trans and gauche conformers in both C2Cl4 and perdeuterioacetone solvents is 879 ± 167 J mol−1 (210±40 cal mole−1). The s‐trans conformer is the most stable, in contrast to the isoelectronic cyclohexylcarboxyaldehyde where the gauche rotamers are lower in energy.
13C NMR spectra of 2,3‐dihydro‐1H‐pyrrolo[1,2‐c]imidazol‐1,3‐dione and its thione analogues
Authors: Budhram Ronald S. , Uff Barrie C. , Jones R. Alan , Jones Richard O.
Published: May 2005

Analysis of the 13C NMR spectra of a series of 2,3‐dihydro‐1H‐pyrrolo[1,2‐c]imidazole derivatives has provided chemical shift data for (˜184 ppm), (˜173.5 ppm), (˜158 ppm) and (˜148 ppm) groups. A full analysis of the 13C chemical shifts of the C atoms of the pyrrole ring and of an N‐phenyl substituent is described.
Comments on the correlations between geometric parameters of molecules and parameters of their 1H NMR spectra: The answer to a criticism
Authors: Vorontsova L. G. , Bochkov A. F.
Published: May 2005

An earlier paper by the authors has undergone criticism by Jankowski and Rabczenko. The arguments presented are analysed in this paper and the criticism is rejected.
Zero‐field‐splitting of some aromatic charge‐transfer complexes in their lowest excited triplet states—an ESR study
Authors: Krzystek Jerzy
Published: May 2005

The ESR spectra of some aromatic charge‐transfer complexes in the lowest excited triplet states were measured. From the extracted zero‐field‐splitting parameters it was found that in each case the lowest excited triplet state was localized on the donor, with a variable contribution of charge‐transfer configuration.
Coupling of HPLC and NMR 1—analysis of flowing liquid chromatographic fractions by proton magnetic resonance
Authors: Buddrus Joachim , Herzog Helmut
Published: May 2005

A procedure is described which allows the recording of 1H NMR spectra from high performance liquid chromatography (HPLC) fractions flowing through the magnetic field with a velocity of either 0.05 or 0.25 cm/s. The NMR spectra are obtained by the pulse Fourier transform technique; the beginning and the termination of the pulse sequence is timed according either to the chromatogram from a UV detector or to the free induction decay of the appropriate HPLC fraction. The linewidth of the signals in the NMR spectra is between 1.5 and 2.0 Hz.
Partial orientation of nitroxide biradicals in the plastic phase of cyclohexane and in frozen toluene solution
Authors: Chiarelli Robert , Jeunet André , Michon Josette , Michon Pierre , Morat Claude , Rassat André , Sieveking Hans Ulrich
Published: May 2005

Several nitroxide biradicals have been studied by electron spin resonance, in cyclohexane solution at −10°C and in toluene solution at −150°C. The ESR spectra change when the sample orientation in the spectrometer cavity is changed: under favourable circumstances oriented spectra are obtained.
13C NMR investigation of flavonoid C‐β‐D‐glucosides. Detection of a conformational equilibrium
Authors: Davoust Daniel , Massias Marcel , Molho Darius
Published: May 2005

Evidence of a slow conformational equilibrium in some flavonoid 6‒C‒β‒D‒glucosides is deduced from examination of their 13C NMR spectra run at room temperature.
The rα‐structure of partially oriented 1,2,3,5‐tetrachlorobenzene determined from its 1H NMR spectra with natural‐abundance 13C‐satellites. A Demonstration of the Combined Use of Spectra Obtained from Molecules Dissolved in Several Different Liquid Crystals as Solvents for Spin Systems not having enough Dipolar Coupling Constants to Determine the Molecular Structure
Authors: Dombi G. , Amrein J. , Diehl P.
Published: May 2005

It is demonstrated that in a case where neither the proton nor the natural‐abundance 13C‐satellite spectra of a partially oriented molecule carry enough structural information, one can determine the entire molecular geometry by the combined use of several liquid crystals as solvents. As an example, the spectrum of 1,2,3,5‐tetrachlorobenzene is analysed and the rα‐structure is computed after vibration corrections of the dipolar coupling constants obtained in two different liquid crystals. The carbon‐hydrogen, carbon‐carbon internuclear distance ratios as well as bond lengths and angles are determined. The solvent effect of the two different nematic phases on the molecular structure is investigated and found to be negligible. Indirect proton‐proton and proton‐carbon couplings, as well as one‐bond and two‐bond 13C isotope effects on the proton chemical shifts, are measured in an isotropic solvent.
Carbon‐13 NMR of 1,2‐indandione and heterocyclic analogues. A reappraisal
Authors: Galasso V. , Pellizer G. , Pappalardo G. C.
Published: May 2005

13C NMR chemical shifts previously reported for 1,2‐indandione and thionaphthenequinone have been found to be erroneous; the correct results have now been established.
Some INDO calculations of fluorine‐nitrogen spin–spin coupling constants
Authors: Khin Tun , Duangthai S. , Webb G. A.
Published: May 2005

INDO parameterized calculations of nJ(19F15N) are reported where n=1, 2, 3, 4 and 5. The calculations are performed within the sum‐over‐states perturbation and self‐consistent perturbation frameworks. In general, satisfactory agreement between both sets of calculated results and the available experimental data is obtained. All of the 1 J(19F15N) and 4J(19F15N) couplings can be of either sign. Most of the couplings considered are dominated by the contact contribution but the non‐contact interactions can be very important in certain cases.
Conformational equilibria in isomeric methylcyclohexanols studied by 13C NMR spectroscopy
Authors: Subbotin O. A. , Sergeyev N. M. , Chlopkov V. N. , Nikishova N. G. , Bundel Yu. G.
Published: May 2005

The conformational equilibrium constants for isomeric methylcyclohexanols (cis‐ and trans‐1,2‐, 1,3‐ and 1,4‐methylcyclohexanols) have been determined from peak area measurements in the completely proton decoupled low temperature 13C NMR spectra of the individual conformers. The 13C chemical shifts are discussed in terms of the additive model.
The 13C NMR spectra of tallysomycin and its zinc(II) complex
Authors: Greenaway Frederick T. , Dabrowiak James C. , Grulich Robert , Crooke Stanley T.
Published: May 2005

Using the carbon assignments of bleomycin A2 as well as those of a series of model compounds, the 13C NMR assignments of the antitumor antibiotic tallysomycin (TLM) have been made. With the aid of the carbon assignments the metal binding properties of the new antibiotic toward Zn(II) have been investigated.
13C chemical shifts and conformational analysis of methyl substituted thiacyclopentanes
Authors: Barbarella G. , Dembech P.
Published: May 2005

The 13C NMR spectra of thiacyclopentane (thiolane) and its mono‐ and dimethyl derivatives at positions other than the heteroatom are reported. The 13C shieldings are found to be consistent with a description of these compounds in terms of equilibria between half‐chair conformers. An attempt has been made to establish the axial or equatorial preference of methyl groups adjacent to, or removed from, the sulphur atom in these systems. In agreement with previous observations on thiacyclohexanes (thianes), the conformational preference of a methyl group for the equatorial orientation is greater at the β than at the α position.
NMR study of 2‐alkoxy‐1,3,2‐dioxaphospholanes. II—molecular conformation of alkoxy substituents
Authors: Besserre D. , Coffi‐Nketsia S.
Published: May 2005

The conformation of some 2‐σ‐1,3,2‐dioxaphospholanes (σ=OAlkyl, CI) is studied. The determination of the 2J(POC) and 3J(POCC) coupling constants, which are influenced by the bulk of the alkoxy group, is a means of obtaining information about the rotation around the POR bond, which is dependent on steric interactions between the phosphorus lone pair, the alkoxy group and the substituents on the ring. When σ is a tert‐butoxy group, a direct ‘through‐space’ interaction is found between the phosphorus atom and one of the primary carbons of the OR group. If there is no substituent on the ring, the 31P chemical shifts are little affected by changes in OR; a diamagnetic effect is observed, however, in the case of the tert‐butoxy group which is enhanced for the 4,4,5,5‐tetramethyl derivatives.
1H NMR study of the reaction of ornithine and lysine with pyridoxal‐5′‐phosphate
Authors: Arcelli Antonio , Bongini Alessandro , Budini Rolando
Published: May 2005

The composition of the mixture from the reaction of the basic amino acids ornithine or lysine with pyridoxal‐5′‐phosphate was investigated in D2O by 1H NMR and was found to be dependent on pH, α attack being favoured at acid pH and ω attack in basic solutions.
13C NMR spectra of s‐triazolo‐as‐triazinones: Application to isomeric and tautomeric structure determination
Authors: Daunis Jacques , Follet Michel , Marzin Claude
Published: May 2005

13C NMR spectroscopic data are reported for the s‐triazolo‐as‐triazinones of five isomeric series. Comparison of their 13C chemical shifts and CH coupling constants allows the determination of the type of ring junction of the two heterocycles, as well as the predominant tautomeric form in each system.
15N NMR spectroscopy. 23—Shift effects of protecting groups in oligopeptides of glycine and alanine
Authors: Kricheldorf Hans R. , Hull William E.
Published: May 2005

The natural abundance 15N NMR spectra of glycylglycine and alanylalanine derivatives with various N‐ or O‐protecting groups were measured in dimethyl sulphoxide, pyridine and fornic acid. The nitrogens directly attached to the protecting group have chemical shifts relative to NO3− in the range −220 to −358 ppm. The influence of the amino end group on the next peptide nitrogen (Gly‐Gly bond) amounts to, at most, 1.7 ppm. The influence of the O‐protecting group is also weak (Δ δ⩽2 ppm), but strongly dependent on the solvent.
Substituent effects on meta‐proton chemical shifts in substituted benzenes
Authors: Batts B. D. , Pallos G.
Published: May 2005

The chemical shifts at infinite dilution and coupling constants of some meta‐substituted nitrobenzenes (C6H4NO2X) were determined in CDCI3 solutions (X = CHO, OCH3, CI, Br, NH2, NO2) and in CCI4 solutions (X = OCH3, CI, Br). Substituent effects on the chemical shift of the meta‐hydrogen are analysed in terms of existing theories.
Substituent effects on 13C NMR chemical shifts in the saturated framework of primary aliphatic derivatives
Authors: Ejchart Andrzej
Published: May 2005

A general equation describing the effect of substituents on α‐carbons in a saturated framework was developed from 13C chemical shifts obtained under uniform conditions for selected aliphatic compounds. Experimental correlations for β‐ and γ‐carbons and a discussion of the results are presented.
Proton nuclear magnetic resonance study of phthalide and 2‐coumaranone partially oriented in nematic phases
Authors: Wong T. C. , Koval Kenneth J.
Published: May 2005

The 1H NMR spectra of phthalide in Merck Nematic Phase IV and in N‐(p‐ethoxybenzylidene)‐p‐n‐butylaniline (EBBA) and of 2‐coumaranone in Merck Nematic Phase IV were analyzed. Structural parameters were obtained. The planarity of the 5‐membered ring and the molecular orientations were discussed.
Radical reactions in the coordination field of transition metals. VII—H‐transfer between phenolic and aryl‐aminic H‐donors and their radicals
Authors: Tkáč A. , Omelka L.
Published: May 2005

An ESR method for studying the mechanism of H‐transfer reactions between H‐donors of different reactivity (A1H, A2H…) and their free radicals (A1; A2.…) in non‐polar solvents at ambient temperature is presented. The new technique is based on a pulsed initiation of various secondary phenoxy or nitroxy radicals in binary mixtures of hindered phenols, unhindered phenols, partially hindered thiobisphenols and diphenylamine, employing a high concentration of free RO2. and coordinated (CoIII)RO2. tert‐butyl peroxy radicals generated in the redox‐reaction of Co(acac)2 with tert‐butyl hydroperoxide. The consecutive H‐transfer reactions proceed to equilibrium until the most stable radicals are formed. In this way criteria are obtained for ranking the compared free and coordinated phenoxy radicals according to their relative stabilities. The secondarily generated phenoxy radicals from unhindered phenols after coordination to CoIII are stabilized and cannot take part in further H‐transfer reactions.
Carbon‐13 nuclear magnetic resonance spectra of nicotine metabolites and related compounds
Authors: Nishida Toshiaki , Pilotti ÅKe , Enzell Curt R.
Published: May 2005

The potential of 13C NMR techniques for studies of nicotine metabolism has been investigated by acquisition and assignment of 13C NMR spectra of nicotine, its metabolites and some related compounds. It is shown that C‐2′ of nicotine would be the best site for 13C labelling when using the method to gain further insight into the metabolic pathways of nicotine.
Temperature dependence of 13C nuclear magnetic shielding in some aliphatic alcohols
Authors: Jackowski K. , Raynes W. T.
Published: May 2005

The 13C nuclear shielding in methanol, ethanol and isopropanol has been measured over the temperature range 186–325 K. Corrections to the observed shifts have been made to allow for the temperature dependence of the shielding of the external tetramethylsilane reference and for the temperature dependence of the bulk susceptibility effects in the alcohols. The results show that the temperature dependence of 13C shielding in the liquid alcohols is smaller than that in tetramethylsilane. By comparison both with temperature coefficients of compounds not involving hydrogen bonding and with N‐protonation studies, it is inferred that the reduction of hydrogen bonding which occurs in the liquid alcohols as the temperature is raised has very little effect on the 13C shielding. It is the change in the van der Waals forces which predominates in determining the temperature coefficient.
Carbon‐13 NMR spectra of bromine‐containing esters
Authors: Velichko F. K. , Dostovalova V. I. , Vinogradova L. V. , Kh. Freidlina R.
Published: May 2005

13CHBrCOOR fragments of bromine‐containing mono‐ and dicarboxylates show 13C NMR signals in the range 38–45 ppm, at 12–15 ppm to high field of their chloro analogues. The introduction of one bromine atom into the α‐CH2 group causes a 6–13 ppm shift of the carbon signal, depending on the type of ester. The replacement of H with Br in 13CH2(COOR)2 has only a negligible influence on the 13CH2 signal position. The 13CBr2COOR fragment signals appear in the range 50–54 ppm. 13C NMR data, including the chemical shift values, signal multiplicities and spin‐spin couplings, make possible the identification of isomers present in isomer mixtures of bromine‐containing esters. The 13COOR chemical shifts of diastereomers of α,β‐dibromoesters differ noticeably from each other, and the 13C NMR spectra can thus be used to supply preliminary information about the stereochemistry of bromine addition to α,β‐unsaturated acids.
Selection of shift reagents for 17O NMR. Application to line assignments
Authors: Kintzinger Jean‐Pierre , Nguyên T. Thanh‐TâM
Published: May 2005

Chemical shifts and line broadenings induced by a series of lanthanide dipivaloylmethanates Ln(dmp)3 on the 17O NMR signal of methanol have been measured. The best high‐field shift reagents are those containing the cations Tb+3 and Dy+3; very large shifts have been observed for even quite low concentrations of reagent. The shift reagents are able to discriminate between different oxygen functions and can, in principle, be used for line assignments.
Primary and secondary binding sites for lanthanide shift reagents with amides. Differential behavior of cis vs trans amide isomers with LSR
Authors: Graham Laurine Laplanche
Published: May 2005

Lanthanide induced shifts (LIS) were measured for four dimethylamides, RCON(CH3)2, and four monomethyl amides, RCONHCH3, R  H, CH3, CF3 and CCl3, using Eu(fod)3 in CCl4 and benzene (C6D6) solution. Structural correlations for HCON(CH3)2 and CH3CON(CH3)2 in both solvents yield a preferred binding site for the Eu(fod)3 on one of the lone‐pair orbitals of the oxygen atom, with a probable site of secondary importance on the other lone‐pair orbital. The cis vs trans isomers of HCONHCH3 and CH3CONHCH3 exhibit remarkably different chemical shift behavior upon addition of Eu(fod)3.
Nitrogen‐15 nuclear magnetic resonance spectroscopy. Differential rates of NH proton‐exchange reactions of hydrazine‐carbothioamide and 4‐methylhydrazine‐carbothioamide in dimethyl sulfoxide
Authors: Yavari Issa , Roberts John D.
Published: May 2005

The proton‐coupled nitrogen‐15 NMR spectra of hydrazinecarbothioamide and 4‐methylhydrazinecarbothioamide have been taken at the natural‐abundance level in neutral, basic and acidic solutions at 25°C. The NH proton‐exchange reactions of the hydrazino‐NH2 groups in both compounds were found to be very rapid in the presence of acid, but quite slow in the presence of base. The hydrazino‐NH protons of hydrazinecarbothioamide exhange six times and 200 times faster than the amide protons in the presence of either base or acid, respectively. Similarly, acid‐ and base‐catalyzed NH proton exchanges of the hydrazino‐NH group of 4‐methylhydrazinecarbothioamide were found to be two to three orders of magnitude faster than those of N‐methylamido protons. These results can be rationalized by consideration of the effect of the lone pair on the hydrazinoNH2 group on the reactivity of the adjacent NH group.
High resolution NMR spectroscopy of heteroaromatic cations. I. 13C1H coupling constants in the pyridinium cation
Authors: Sándor P. , Radics L.
Published: May 2005

High‐resolution 1H{14N} and proton‐coupled natural‐abundance 13C{14N} double resonance spectra have been recorded for pyridinium tetrafluoroborate dissolved in CD3CN. Iterative analysis of these spectra has provided the accurate values and relative signs of all possible long‐range 13C—1H coupling constants. These are compared with the respective values in pyridine and pyridine‐N‐oxide and discussed in terms of the relationship with the electronegativity of the N‐substituent. Experimental conditions allowing the observation of well‐resolved proton‐coupled 13C NMR spectra of charged heteroaromatics are also presented.
Carbon‐13 nuclear magnetic resonance studies of anthraquinones Part II—hydroxymethoxyanthraquinones, acetoxymethoxyanthraquinones and naturally occuring anthraquinone analogues
Authors: Berger Y. , Castonguay A. , Brassard P.
Published: May 2005

The 13C NMR spectra of hydroxymethoxyanthraquinones, acetoxymethoxyanthraquinones and naturally occuring anthraquinone derivatives are reported and all chemical shifts assigned. Hydroxy, methoxy and acetoxy substitution parameters are additive except in the case of 1,2‐disubstitution and for 1‐hydroxyanthraquinones substituted on C‐3 or on C‐4 by an hydroxy or a methoxy group. In anthraquinones substituted on C‐2, carbon shieldings are found to be sensitive to steric interference and to conjugative electron release by the 1‐OCH3.
Radical reactions in the co‐ordination field of transition metals. VIII—σ‐phenoxy and σ‐cyclohexadienoneoxy radicals co‐ordinated to cobalt (III) and their generation by tert‐butylperoxy radicals or by molecular oxygen complexed to cobalt
Authors: Tkáč A. , Omelka L.
Published: May 2005

The formation of a ternary complex between phenols, Co (II)‐acetylacetonate and molecular oxygen has been established at ambient temperature and in non‐polar solvents. After intramolecular electron transfer the transient magnified image radical enhances the homolytic scission of the OH bond of the complexed phenol. The low g value of the observed ESR spectra, the net spin delocalization to the cobalt nucleus and the interaction of the unpaired electron with only a limited number of benzene ring protons, indicate the presence of co‐ordinated s̀‐phenoxy radicals generated from unhindered phenols (g = 2.0006 ∼ 1.9997) and of co‐ordinated s̀‐cyclohexadienoneoxy radicals generated from hindered phenols (g=1.9990 ∼ 1.9980). Without the cobalt‐chelating acetylacetonate ligands neither the co‐ordinated s̀‐phenoxy nor the co‐ordinated s̀‐cyclohexadienoneoxy radicals can be prepared, whereas co‐ordinated π‐tert‐butylperoxy radicals [Co(III)BuO2·] are generated in a high concentration during the reaction of tert‐butyl hydroperoxide with CoCl2 in acetone.
Dynamic stereochemistry at sp2sp3 bonds part 1—the use of heterocyclic models for quantitative studies of steric effects of alkyl groups
Authors: Roussel Christian , Gallo Roger , Metzger Jacques , Sandström Jan
Published: May 2005

The barriers to rotation of the 3‐substituent in six 3‐RCH2‐4‐Me‐δ4‐thiazoline‐2‐thiones (R  Me, Et, Pr, Isobu, Isopr,t‐Bu) and in two analogous methiodides have been measured by the 1H DNMR technique. The barriers are discussed in relation to the possible conformations of the transition states, and comparisons are made with barriers to rotation of the same substituents in other frameworks. It is concluded that the relative steric effects are strongly dependent on the framework and that, in general, a conformational analysis of the individual cases is necessary to understand the steric effects of alkyl groups.
Quantitative 15N NMR spectroscopy
Authors: Levy George C. , Pehk T. , Srinivasan P. R.
Published: May 2005

Line intensities in 15N NMR spectra are strongly influenced by spin‐lattice and spin–spin relaxation times, relaxation mechanisms and experimental conditions. Special care has to be taken in using 15N spectra for quantitative purposes. Quantitative aspects are discussed for the 15N NMR of molecules with different nitrogen functional groups and also mixtures of nitrogen‐containing compounds. It is shown that, in general, quantitative data are obtainable from integration of 15N lines in proton decoupled 15N NMR spectra using NOE suppression. Addition of paramagnetic relaxation reagents (PARR) under controlled conditions is frequently needed to accomplish the experiment within reasonable time limits.
Restricted rotation of the C6F5 ligand in cyclopentadienyl π‐complexes of titanium (IV)
Authors: Leblanc Jean Claude , Moïse Claude
Published: May 2005

1H and 19F spectra of methoxypentafluorophenyltitanocene complexes have been analysed. They show the possibility of coupling between the methyl protons of the methoxy group and the two ortho fluorine atoms of the pentfluorophenyl ligand. Furthermore, anisochrony of the two ortho and the two meta fluorine atoms is detected in some cases. The analysis of conformational factors is presented.
Dynamic stereochemistry at sp2sp3 bonds part II—the importance of ground‐state strain in the determination of apparent spatial requirements of substituents
Authors: Roussel Christian , Blaive Bruno , Gallo Roger , Metzger Jacques , Sandström Jan
Published: May 2005

The barriers to rotation of RCH2 groups (R  Me, Et and Isopr) as 3‐substituents in 4‐Me‐δ4‐thiazoline‐2‐thiones, their 4‐t‐Bu analogues, and the methiodides of the latter compounds have been studied by 1H DNMR and by molecular mechanics calculations. The barriers in the 4‐t‐Bu compounds are rather insensitive to the size of R, which is shown to be caused by strain in the ground state. More generally, it is shown that when δG‡ values are used in various methods for estimating the apparent spatial requirements of substituents, such ground‐state strain may lead to erroneous results in non‐circumspect treatments.
Application of 13C NMR to the study of the tautomerism of some disymmetric triazenes: The 3‐aryl‐1‐(3,4‐dimentyl‐5‐isoxazolyl)triazenes
Authors: Vernin G. , Siv C. , Bouscasse L. , Metzger J. , Faure R. , Vincent E. J. , Párkányi C.
Published: May 2005

The 13C NMR spectra of some 1,3‐diaryltriazenes, 3(1)‐aryl‐1(3)‐hetaryltriazenes and their methylated derovatives have been recorded. From the comparison of the 13C chemical shifts between 3‐aryl‐1‐(3,4‐dimethyl‐5‐isoxazolyl)triazenes 1 and compounds with fixed structure, such as 1‐aryl‐3,3‐dimentyltriazenes and methylated derivatives of 5‐amino‐3,4‐dimethylisxazole, we found that the triazenes 1 have the sturcture (A) in which the azo group is conjugated with the heterocycllic moiety. para‐Substituent on the aromatic ring have a week influence on the displacement of this tautomeric equilibrium. 13C NMR gives only qualitatives results. Theoretical calculation (HMO, CNDO‐2) are also consistent with the greater stability of tautomeric form A.
Radical reactions in the co‐ordination sphere of transition metals. X—radicals derived from 4,4‐biphenyldiols, 4,4′‐thiobisphenols and bis(4‐hydroxybenzyl)sulphide
Authors: Tkáč A. , Omelka L. , Jiráčková L. , Pospíšil J.
Published: May 2005

Using the analysis of the splitting constants of the ESR spectra, factor are described which affect the stability of free phenoxyls and of phenoxyls co‐ordinated on cobalt, generated by the reaction of tert‐butyleperoxyls and 4,4′‐biphenyldiols (1), 4,4′–thiobisphenols (2 and 5), 4,4′‐dithiobisphenol 3a, the 4,4′‐trithiobisphenol 3b, di(3,5‐di‐tert‐butyl‐4‐hydroxybenzyl) sulphide (4a) and its corresponding sulphoné (4b). Phenoxy radicals are formed from compounds of type 1–4 in the presence and in the absence of oxygen. In the case of generation with oxygem complexed to cobalt, compounds 4, for steric reasons, form co‐ordinated radicals of the cyclohexadienonyloxyl type. Free phenoxyls are also formed from 2a–2c, 3a and 3b as a result of the direct transfer of electrons from the sulphur non‐bonding electron pair to the peroxidic bond of tert‐butyl hydroperoxide in the absence of cobalt.