bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculation of some 13C nuclear screening constants
Authors: Ebraheem K. A. K. , Webb G. A. 
Published: May 2005

Abstract13C screening constants and their anisotropies are calculated within the CNDO/S framework by using gauge dependent atomic orbitals in the molecular orbital description. The calculations include the excited singlet states which are mixed with the ground state by an external magnetic field. Reasonable agreement with available experimental data is obtained in most cases. Comparisons with some ab initio results are also made.
Interactions intramoléculaires. XXVI—Constantes de couplage et hétérogénéités conformationnelles dans une série de R‐3 et R‐5 cyano‐4 cyclohexènes deutériés (R=méthyl ou t‐butyl)
Authors: Lafrance Ronald , Aycard Jean‐Pierre , Bodot Hubert 
Published: May 2005

AbstractPour les R‐3 et R‐5 acétoxy‐1 cyano‐4 cyclohexène D2‐6,6 trans, les fractions molaires des conformères diéquatoriaux ont été évaluées: 0,83 (méthyl‐3), 0,68 (méthyl‐5), 0,57 (t‐butyl‐3) et 0,55–0.69 (t‐butyl‐5). Pour les deux derniers composés, les valeurs des constantes de couplage sont compatibles avec l'hypothèse d'équilibres ee⇄aa. Pour les isomères cis, les conformères à groupement alkyle équatorial sont prédominants (fraction molaire 0,76 pour méthyl‐3 et méthyl‐5) ou exclusifs (t‐butyl‐3‐butyl‐5). Par contre, l'acétoxy‐1 t‐butyl‐3 méthoxycarbonyl‐45 cyclohexène cis présente une hétérogénéité conformationnelle. L'enthalpie libre conformationnelle du groupement méthyle en position 4 est évaluée à −0,6 kcal mol−1 (2,5 kJ mol−1).
The reactions of transition metal chelates with organometallic compounds and their paramagnetic products. V—New possibilities in the generation of anion radicals by reactions of Grignard reagents and lithium alkyls in the presence of transition metal ions
Authors: Staško A. , Malík L. , Tkáč A. , Adamčík V. , Hronec M. 
Published: May 2005

AbstractIn the reactions of Grignard reagents and n‐butyllithium the presence of transition metals and complexing solvents facilitates the formation of anion radicals. High radical concentrations, observable for some days at laboratory temperature, and very well resolved e.s.r. spectra of the following structural types have been obtained using a relatively simple procedure: aromatic hydrocarbons, heteroaromatics, aldehydes, ketones, α‐diketones, enolates of β‐diketones, quinones, sulphones, sulphoxides, nitro‐, nitroso‐ and azo‐benzenes, cyano compounds and phosphine oxides. It is suggested that the transition metals, according to the type of reactants and the experimental conditions, mediate the transfer of one electron to the substrate in many reactions and stabilize the intermediate products as anion radicals. The variation of solvents and organometallic compounds modifies the reduction power of such systems and leads to the radical products in a different reduction state. The procedure described is advantageously employable in the generation of anion radicals, and the effect of transition metals which has been found may widen the scope of this phenomenon to many different applications.
The gear effect. VII—Conformational analysis of methyl N,N‐diisopropylcarbamate, its thiol and diseleno analogues. An experimental proof for a two‐step conformational interconversion mechanism
Authors: Liljefors Tommy , Sandström Jan 
Published: May 2005

AbstractThe conformations of the isopropyl groups and the barriers to conformational interconversion in methyl N,N‐diisopropylcarbamate, its thiol and seleno analogues have been studied by 1H d.n.m.r. In the diselenocarbamate, complete bandshape analysis of the Se‐methyl proton signals proves unequivocally that the conformational interconversion takes place by rotation of one isopropyl group at a time rather than by a concerted rotation of both groups. The populations and barriers observed for the new compounds fit well into the general scheme found previously for other N,N‐diisopropylamides and ‐thioamides.
Group IVB organometallic compounds of furan: 13C, 29Si and 119Sn n.m.r. Spectra
Authors: Mägi M. , Lippmaa E. , Lukevics E. , Erĉak N. P. 
Published: May 2005

AbstractThe 13C, 29Si and 119Sn chemical shifts of 2‐ and 2,5‐substituted organometallic (M=C, Si, Ge, Sn, Pb) derivatives of furan were measured. The most important factors, determining the specific features of the studied spectra, are d‐orbital availability and atomic radius of the central atom M, as well as the relatively higher (as compared with benzene) energies of the π‐electron energy levels of the furan ring.
Behinderte Rotationen um CC‐ und CN‐Bindungen in Enaminothioketonen mit verschiedenen N‐Substituenten
Authors: Kleinpeter E. , Pulst M. 
Published: May 2005

AbstractIn einer Reihe 1,2‐Diphenyl‐enaminothioketone werden behinderte Rotationen um CN‐ und CC‐Bindungen beobachtet. Die freien Aktivierungsenthalpien ΔG≠ dieser dynamischen Prozesse werden bestimmt und hinsichtlich Delokalisierung des freien Elektronenpaares am Stickstoff der verschiedenen Aminogruppen sowie deren Basizität diskutiert.
N.m.r. spectra of cyclic amines. II—Factors influencing the chemical shifts of α‐protons in aziridines
Authors: Breuer Eli , Somekh Lila , Ringel Israel 
Published: May 2005

AbstractProton magnetic resonance spectra of trans and cis‐2,3‐diphenylaziridine (1 and 2) and their N‐ethyl derivatives 3 and 4 were measured in carbon tetrachloride, chloroform, and benzene‐d6 at low temperatures (1 and 3) and in dry conditions (1 and 2). On the basis of these results it was concluded that an N‐ethyl group exerts a shielding influence on a cis ring proton and a deshielding influence on a trans ring proton. From results obtained by measuring the 1H n.m.r. spectra of 1–4 in deuterochlorofom‐trifluoroacetic acid it was derived that the lone pair of the aziridine nitrogen exerts a shielding influence on cis related ring hydrogens. In most N‐alkylaziridines the effect of the N‐alkyl group predominates.
Theoretical nuclear spin–spin coupling constants using atom–atom polarizabilities. 13CH and HH′ coupling constants of some [2.2.1] bicyclic compounds using the INDO approximation
Authors: Joela Heikki 
Published: May 2005

AbstractTheoretical nuclear spin–spin coupling constants are calculated using mutual and self atom–atom polarizabilities according to a theory where no semi‐empirical parameters are used, except Slater exponents which can be obtained from other sources. As an application, the 13CH and HH′ couplings of some [2.2.1] bicyclic compounds are calculated with the aid of INDO molecular orbitals and compared with the experimentally obtained coupling constants.
Nuclear magnetic resonance studies on some cyclic esters containing the t‐butyl group
Authors: Hellier Desmond G. , Webb Frederick J. 
Published: May 2005

AbstractThe high resolution proton magnetic resonance spectra of a series of cyclic inorganic esters and analogous 1,3‐dioxans have been analysed. The coupling constants and chemical shifts involved indicate that most of the compounds exist preferentially in a chair form.
Structural studies by 1H and 13C dynamic n.m.r.: Part III alternative protonation sites in carbonyl conjugated enamines of the type R1C(O)CHCHNR2R3
Authors: Kozerski Lech 
Published: May 2005

Abstract13C magnetic resonance spectra of several enamino ketones with secondary and tertiary amino groups were obtained for trifluoroacetic acid solutions. In both series O‐protonation is predominant and the chemical shifts are related to the electron density changes with respect to the parent base. The spectra of the tertiary compounds are interpreted in terms of slow rotation around the C–1C–2 and C–3N bonds discernible at room temperature. O‐protonated forms of the secondary enamino ketones undergo further reaction on C–2 yielding pyridinium salts. The mechanism of formation of the quaternary salts is interpreted and the additivity parameters of the 13C n.m.r. chemical shifts in the pyridinium ions is briefly discussed.
Silicon‐29 and carbon‐13 n.m.r. studies of organosilicon chemistry. VII—trimethylsilylated silicates
Authors: Harris R. K. , Newman R. H. 
Published: May 2005

AbstractSilicon‐29 n.m.r. was used to study the products from trimethylsilylation of minerals. Chemical shifts are reported for four model compounds, viz. the monomer, dimer, linear trimer (from natrolite) and cyclic tetramer (from laumontite). Information is then obtained from the products of trimethylsilylation of the anhydrous calcium silicates wollastonite and pseudo‐wollastonite. In the latter case it is shown that the principal products are the four model compounds, and percentage yields are obtained for these.
Silicon‐29 and carbon‐13 n.m.r. studies of organosilicon chemistry. VIII—Assignment of the 29Si and related 1H resonances of trimethylsilylated sugars by deuteration and shift reagent studies
Authors: Haines Alan H. , Harris Robin K. , Rao Renée C. 
Published: May 2005

AbstractTwo techniques were investigated for assigning the 29Si n.m.r. spectra of trimethylsilylated sugars. Specific deuteration, together with selective proton decoupling experiments, has allowed the complete assignment for methyl 2,3,4,6‐tetra‐O‐trimethylsilyl‐α‐D‐glucopyranoside. Double resonance spectra obtained in the presence of a lanthanide shift reagent, Pr(dpm)3, have enabled the 29Si and 1H signals for the ‐SiMe3, groups of methyl 2,3,4‐tri‐O‐trimethylsilyl‐α‐D‐glucopyranoside, to be linked. A complete and unambiguous assignment of the 29Si spectrum for this molecule was obtained by selective deuteration, thus giving an unequivocal assignment of the –SiMe3 proton resonances also. Definitive data regarding the effects of Pr(dpm)3 on the 29Si and 1H resonances of the various –SiMe3 groups of methyl 2,3,4‐tri‐O‐trimethylsilyl‐α‐D‐glucopyranoside are therefore available.
Radikale aus Polymethin‐Farbstoffen. IV—Dikation‐Radikale aus Polymethincyanin‐Farbstoffen mit Indolenin‐Endgruppen
Authors: Oehling H. , Baer F. 
Published: May 2005

AbstractDurch elektrolytische Oxidation konnten aus dinuklearen Polymethincyanin‐Farbstoffen Dikation‐Radikale erzeugt werden. Ihre ESR‐Spektren bestätigen die erwartete Struktur der Radikale.
Benzo‐ and indolo‐quinolizine derivatives XI—The configurational and conformational study of 1,2,3,4,4a,6,7,8,9,13b‐decahydro‐9aH‐pyrido[1,2‐f]phenanthridine isomers by 270 MHz 1H n.m.r.
Authors: Van Binst G. , Laus G. 
Published: May 2005

AbstractThe preferred conformations of the four isomers of 1,2,3,4,4a,6,7,8,9,13b‐decahydro‐9aH‐pyrido[1,2‐f] phenanthridine have been determined by 270 MHz 1H n.m.r. and i.r. spectroscopy. N.m.r. assignments are based on the specific chemical shifts of the protons adjacent to the nitrogen atom, their geminal coupling constants and on the shifts induced by the CC bonds and by the benzene nucleus. Specifically deuterated derivatives and double resonance experiments confirm the assignments unequivocally. These data are completed by solvent and temperature studies.
Calculations of the 13C nuclear screening tensors for coumarin and some methoxycoumarins
Authors: Grigor G. I. , Webb G. A. 
Published: May 2005

AbstractINDO calculations are reported of the 13C nuclear screening tensors in coumarin and some of its methoxy derivatives. Calculations based upon a linear combination of gauge dependent atomic orbitals and those using an uncoupled Hartree–Fock approach are described. Comparison with the results of less sophisticated calculations shows that changes in the excitation energies, bond orders and the 〈r−3〉2p term are together responsible for determining the 13C chemical shifts.
An 1H n.m.r. study of complexation and self‐association processes in the ternary system: tert‐butyl alcohol–acetone–cyclohexane
Authors: Balevichius V. , Kimtys L. 
Published: May 2005

AbstractThe hydroxyl proton chemical shifts of tert‐butyl alcohol, dissolved in acetone and in binary mixtures of acetone with cyclohexane, have been measured as functions of concentration at temperatures of 20, 35, 50 and 60 °C. Using both the equilibrium constant and the quasi‐lattice methods for the interpretation of experimental data, the thermodynamic parameters of self‐association and complexation have been determined, and their dependences on the solvent composition have been analysed. The chemical shifts of the hydroxyl proton obtained in the complexes and the thermodynamic parameters of complexation of tert‐butyl alcohol with acetone‐d6 proved to be the same as for the tert‐butyl alcohol–acetone system.
Effect of substituents on the 1H n.m.r. spectra of para‐disubstituted benzenes. A graphical aid in the correct assignment of chemical shifts
Authors: Holík Miroslav 
Published: May 2005

AbstractIn para‐disubstituted benzenes, the effect of one substituent is transferred to the other composite substituent group and its decreased influence on the ortho and meta protons is reflected in their chemical shifts. A graphical presentation of this linear non‐additive dependence can serve as an aid in the correct assignment of the corresponding aromatic region of the spectra. The method is demonstrated on two series of chemical shift data taken from the literature.
Investigation of the torsional angle at the glycosidic bond in 5′‐amino‐5′‐deoxythymidine derivatives by carbon‐13 n.m.r. spectroscopy
Authors: Nottoli Eileen M. , Lambert Joseph B. , Letsinger Robert L. 
Published: May 2005

AbstractThe conformational preference of the thymine base ring with respect to the sugar ring in β,β,β,‐trichloroethyl 5′amino‐5′‐deoxythymidine‐5′‐phosphate has been studied by 13C n.m.r. spectroscopy. The magnitude of the three bond vicinal coupling constant, J(C‐2, H‐1′), for β,β,β‐trichloroethyl 5′‐amino‐5′‐deoxythymidine‐5′‐phosphate and the similarity between the chemical shifts for the furanose carbons C‐1′, C‐2′, and C‐3′ in β,β,β‐trichloroethyl 5‐′‐amino‐5′‐deoxythymidine‐5′‐phosphate and in β,β,β‐trichloroethyl thymidine 5′‐phosphate indicate that the amino analogue exists in aqueous solution predominantly in the anti conformation, as is the case with natural nucleotides.
RMN du 13C de Bromo et de Fluoro Cyclanones à Structure Contrainte: Variation des Effets α et γ en Fonction des Facteurs Stériques et de la Nature de l'Halogène
Authors: Reisse J. , Piccinni‐Leopardi C. , Zahra J. P. , Waegell B. , Fournier J. 
Published: May 2005

AbstractOn décrit les spectres de RMN du 13C de diverses halogéno bicyclo[3.2.1]octanone‐3 et diméthyl‐7,7 bicyclo[3.1.1]heptanone‐3. S'il s'avère impossible de faire des corrélations systématiques au niveau des effets β, il est par contre possible de relier semi‐quantitativement les effets α et γ aux facteurs géométriques. La RMN du 13C permet ainsi d'appréhender les effets réflexe et anti‐réflexe.
Le Spectre de L'Alcool Propargylique en Fonction du pH. Un Exemple de Transferts Protoniques Complexes sur un Diacide Organique
Authors: Bouatouch K. , Chrisment J. , Delpuech J‐J. , Nicole D. 
Published: May 2005

AbstractLe diméthylsulfoxyde (DMSO) est utilisé comme solvant pour étudier l'acidité cinétique de très faibles diacides organiques par RMN du proton. Un examen du spectre de l'alcool propargylique en fonction du pH met en évidence less mécanismes de transfer suivants:magnified image.
13C nuclear magnetic resonance studies of saturated heterocycles: II—substituent effects on the 13C chemical shifts of methyl substituted 1,3‐dithianes and their application to the determination of conformational equilibria
Authors: Pihlaja Kalevi , Björkqvist Börje 
Published: May 2005

AbstractThe 13C chemical shifts for 1,3‐dithiane and 9 methyl substituted derivatives are reported. Only three of the methyl‐1,3‐dithianes were conformationally anancomeric and hence the conformational equilibria must be taken into account when deriving the values of the different substituent effects on the 13C chemical shifts. The best fit for each substituent effect was obtained when –ΔGθ (5a‐Me) for 5‐methyl‐1,3‐dithiane was given the value 3.8 ± 0.3 kJ mol−1 and when the difference between –ΔGθ (2a‐Me) and –ΔGθ (5a‐Me) for cis‐2,5‐dimethyl 1,3‐dithiane equalled 3.4 ± 0.4 kJ mol−1. The conformer populations chosen from our earlier paper1 were then suitable for all the other conformational equilibria in question. The magnitude of the derived substituent effects are compared with those for cyclohexane and 1,3‐dioxane.
Spectroscopic characterization of some chlorinated tricyclic hydrocarbons of the C10 series: Chlordanes, chlordenes and nonachlors
Authors: Wilson Nancy K. , Sovocool G. Wayne 
Published: May 2005

AbstractCarbon‐13 and proton nuclear magnetic resonance (n.m.r.) spectra of ten chlorinated hydrocarbons, which are components of technical chlordane and one chlordane metabolite, were examined. For chlordene, dichlorochlordene, cis‐ and trans‐nonachlor, and cis‐ and trans‐chlordane, whose chemical structures are well‐established, the relationships between the n.m.r. parameters and these structures were investigated. The results allow confirmation of proposed structures for α‐, β‐, and γ‐chlordene. A structure, corresponding to 2,4,5,5,6,7,8,8‐octachloro‐2,3,3a,4,5,7a‐hexahydro‐1,4‐methano‐1‐H‐indene, is proposed for another chlordane component, previously known only as Compound K.
Arithmetic manipulation of coupling constants to obtain torsional angles
Authors: Lambert Joseph B. , Sun Hsiang‐ning 
Published: May 2005

AbstractVarious arithmetic combinations of Jtrans and Jcis from the AA′BB′ analysis of CH2—CH2– fragments in 6‐membered rings have been examined for their relationship to the internal torsional angle Ψ. The simple ratio R (Jtrans/Jcis) appears to offer the most complete removal of substituent electronegativity effects and hence the best values of Ψ. The Karplus equation is very inaccurate when the substituents are highly polar. The simple difference D (Jtrans–Jcis) overcompensates for electronegativity effects and thus also gives relatively inaccurate torsional angles. An alternative, artificial linear combination of the coupling constants, such as D′ (Jtrans–2Jcis), appears to be able to provide torsional angles that are almost as good as those from the R value, although the Karplus A value must be evaluated. Adjustment of the simple difference D for electronegativity is possible by including a function of the AA′ and BB′ chemical shifts. These results are fairly good, and the parameter A need not be evaluated. This approach may fail, however, with particularly anisotropic substituents, since the chemical shift may depend on factors other than electronegativity. Although all five methods give reasonably good results, the R value appears to offer the most reliable results for the full range of substituents.
Détermination Univoque des Déplacements Chimiques des Protons Axiaux et Équatoriaux dans une α‐Bromo Cyclohexanone. Une Application de la Mesure des Temps de Relaxation Longitudinaux des Protons
Authors: Pouzard G. , Hall L. D. , Zahra J. P. , Waegell B. 
Published: May 2005

AbstractL'étude des constantes de couplage à longue distance entre protons et la mesure des temps de relaxation longitudinaux des protons de la bromo‐2 tétraméthyl‐3,3,5,5 cyclohexanone (BTC) permettent l'identification de tous les protons axiaux et équatoriaux. Cette attribution confirme la stéréochimie des couplages à longue distance 4J(HH) et elle est en accord avec les facteurs structuraux qui découlent de la théorie de l'Effet Réflexe.
The 13C,H coupling constants in structural and conformational analysis: II The correlation of 3J(HCCH) and 3J(CH3CCH) in ethylenes and their methyl derivatives
Authors: Äyräs Pertti 
Published: May 2005

AbstractThe vicinal 3J(CH3CCH) coupling constants were determined for a number of propylene derivatives and compared with the 3J(HCCH) couplings of the corresponding ethylenes. A linear regression analysis yielded the correlation 3J(CH) = 0.46 ×3 J(HH)+1.58 Hz, the correlation coefficient being 0.956.
Progress in nuclear quadrupole resonance investigations of halogen‐containing organic and organometallic compounds
Authors: Voronkov M. G. , Feshin V. P. 
Published: May 2005

AbstractRecent nuclear quadrupole resonance (n.q.r.) investigations of halogen‐containing organic and organometallic compounds, covering the period between 1970–1976, are reviewed. Special attention is paid to n.q.r. studies of the stereochemistry of organic molecules with particular emphasis on the interactions of geminal atoms, and the application of Stark effects to the study of the coordination and hybridization of atoms.
Three nuclei n.m.r. spectroscopy of dimethoate compounds. A large solvent effect on the 31PSC1H vicinal coupling
Authors: Paasivirta Jaakko , Simanainen Jarmo , Vesterinen Raili , Virkki Liisa 
Published: May 2005

AbstractProton, phosphorus and carbon magnetic resonance spectra of dimethoate, dimethoxon, des‐N‐methyldimethoate, ω‐hydroxydimethoate, trimethyldithiophosphate and O,O‐dimethyldithiophosphate in different solvents have been measured. Most of the n.m.r. parameters were characteristic of the structural environment of the corresponding nucleus and solvent‐independent. However, in the amide structures dimethoate, dimethoxon, des‐N‐methyldimethoate and ω‐hydroxydimethoate the 31PSC1H vicinal coupling showed an unusually large solvent effect of a 2.3 to 6.5 Hz decrease when CDCI3 was replaced by acetone‐d6 or DMSO‐d6.
Carbon‐13 n.m.r. studies: 68—diastereomeric nonequivalence and the characterization of some bisnorbornylpinacols
Authors: Stothers J. B. , Teo K. C. 
Published: May 2005

AbstractThe sodium‐ammonia reduction of racemic norcamphor, exo‐3‐methylnorcamphor and 3,3‐dimethyl‐norcamphor (camphenilone) leads to substantial yields (60–90%) of the corresponding 2,2′‐bisnorbornyl‐2,2′‐diols as diastereomeric mixtures. A combination of their 1H, 13C and infrared spectra together with the results of periodic acid and lead tetraacetate oxidations permits stereochemical assignments for these six pinacols.
Etude en RMN 13C de Spiropyrannes Hétérocycliques
Authors: Appriou P. Y. , Samat A. M. , Guglielmetti R. J. , Le Gall J. Y. 
Published: May 2005

AbstractUne étude en RMN du carbone‐13 d'une série de spiropyrannes qui diffèrent par leur partie hétérocyclique a été réalisée. Nous avons tenté d'évaluer l'influence spécifique des divers hétéroatomes sur le déplacement chimique des atomes voisins. Les déplacements chimiques et les constantes de couplage J(CH) ont également été déterminés pour les composés analogues à chacune des deux parties constitutives de la molécule de spiropyranne: hétérocycle et benzopyranne.
Use of lanthanide shift reagents for the determination of the alkyl conformation in 2‐alkyl‐2‐adamantanols
Authors: Hájek M. , Trška P. , Vodička L. , Hlavatý J. 
Published: May 2005

AbstractThe position of the lanthanide atom calculated from the pseudocontact shift equation was studied for 2‐adamantanol and 2‐methyl‐, 2‐ethyl‐, 2‐propyl‐, 2‐butyl‐2‐adamantanol. The possible methods of calculation considering rotation of the methyl group were ascertained in the case of 2‐methyl‐ and 2‐ethyl‐2‐adamantanol. It follows from these results that a 2‐alkyl group affects the effective position of the lanthanide atom. The conformational analysis of 2‐ethyl‐2‐adamantanol demonstrates a difference among conformations obtained with various shift reagents. A comparison with extended Huckel theory calculations shows that the shift reagent method can be used only for a qualitative determination of the most advantageous conformation of the ethyl group.