bluuebunny/crossref_metadata_2025_split huggingface dataset:
CIDNP effects in various magnetic fields during the reaction of substituted benzyl chlorides with n‐butyllithium
Authors: Sagdeev R. Z. , Molin Yu. N. , Salikhov K. M. , Leshina T. V. , Kamha M. A. , Shein S. M. 
Published: May 2005

AbstractWe detected and studied CIDNP effects in the reaction of substituted benzyl chlorides with n‐butyllithium in hexane (Scheme 1) in various magnetic fields (from 0·5 Oe to about 25,000 Oe). The polarisation of 19F nuclei in the reaction of p‐F‐benzyl chloride in strong fields has been observed by Rakshys.1 We succeeded, however, in finding the CIDNP effects for both 19F and 1H in all the reactions investigated. The CIDNP effects observed offer a number of remarkable features; therefore, a detailed analysis of these effects can be useful for a better understanding of the nature of CIDNP.
Conformational studies of monoterpenes. II–conformational studies of bicyclo[3.1.1]heptane derivatives by 13C NMR
Authors: Holden Collette M. , Whittaker David 
Published: May 2005

AbstractThe carbon‐13 spectra of seventeen bicyclo[3.1.1]‐heptane derivatives have been recorded and assigned. Study of the C‐6 and C‐7 chemical shifts permits the conformations to be assigned to the bridged chair, Y‐shaped, or bridged boat conformations. The spectrum of verbenone is anomalous and is compared to that of umbellulone recorded earlier.
Mesomere Kationen. IV—13C‐NMR‐Spektren von Uronium‐, Thiouronium‐ und Guanidiniumsalzen, sowie einigen Guanidinen
Authors: Kalinowski Hans‐Otto , Kessler Horst 
Published: May 2005

AbstractDie 13C‐NMR‐chemischen Verschiebungen von Uronium‐, Thiouronium‐ und Guanidiniumsalzen werden mit den entsprechenden ungeladenen Harnstoffen, Thioharnstoffen und Guanidinen verglichen. Die chemischen Verschiebungen der aromatischen Kohlenstoffatome geben in Zusammenhang mit den entsprechenden Phenolen und Thiophenolen einen Einblick in die Ladungsverteilung in diesen Systemen.
Etude conformationnelle d'acyl‐2 et acyl‐3 furannes par RMN
Authors: Fournié‐Zaluski M. C. , Roques B. P. , Chatain‐Cathaud C. 
Published: May 2005

AbstractLes déplacements chimiques des protons d'aroyl‐2 et ‐3 furannes (α‐thénoyle, α‐furoyle, benzoyle) 1 et 2 ont été interprétés en termes de conformations préférentielles et ont permis de comparer les énergies de conjugaison de ces différents groupements. Le groupe thénoyl‐2 conserve toujours une disposition OS cis alors que le groupe furoyl‐2 ne possède aucune préférence conformationnelle.
A NMR study of trimethylacetic acid self‐association
Authors: Kimtys L. 
Published: May 2005

AbstractThe carboxyl proton chemical shifts of neat trimethylacetic acid and its solutions in cyclohexane have been measured as a function of temperature. Formation, at the melting point, of a carboxyl group satellite line on the low field side has been found. The intensity of this satellite line rises with decreasing temperature, whereas the intensity of the main line decreases. The chemical shifts of the monomer (δm = 4·9 ± 0·6 ppm) and dimers, the equilibrium constants, enthalpy (ΔH = −(11·3 ± 0·6) kcal/mol) and entropy (ΔS = −(13·5 ± 0·7) cal/mol. degree) changes have been calculated using the concentration dependence of the chemical shifts of trimethylacetic acid in cyclohexane solutions at various temperatures. The chemical shift of the satellite line has been shown to correspond to the chemical shift of the cyclic dimers of the acid.
1H NMR spectra and ring shapes of the 4,5,8‐trimethyl and 4‐methyl derivatives of 1‐tetralone
Authors: Cook Michael J. , Hock Teh Kim 
Published: May 2005

AbstractThe 220 MHz spectra of the title compounds are reported and values for the internal ring dihedral angle, Ψ, formed between the C‐2C‐1 and C‐3C‐4 bonds, calculated using the R‐value method. The trimethyltetralone exists in a conformer having Ψ = 51° and the 4‐methyl group in the axial position. 4‐Methyl‐1‐tetralone exists in a conformational equilibrium where the mean value of Ψ for the conformers adopted is 56°.
Etude par RMN du Proton et du Carbone‐13 de Pyrimidines Substituées. I—Effets de Substituant dans les Dérivés Méthylés et Aminés
Authors: Riand J. , Chenon M. T. , Lumbroso‐Bader N. 
Published: May 2005

AbstractLes effets de substituant des groupes méthyle et amino sur les déplacements chimiques de la pyrimidine ont été étudiés par RMN du proton et du carbone‐13 et comparés à ceux observés pour le benzène et la pyridine. Compte‐tenu des interactions mutuelles des substituants, les déplacements chimiques calculés à l'aide d'un schéma d'additivité sont en très bon accord avec les déplacements chimiques observés, sauf dans quelques cas concernant des pyrimidines encombrées. Cette étude des effets de substituant a permis l'attribution sans équivoque des spectres du carbone‐13 de pyrimidines trisubstituées.
Assignment of juvabione diastereomers by 13C nuclear magnetic resonance spectroscopy
Authors: Manville John Fieve , Bock Klaus 
Published: May 2005

AbstractThe determination of structures and partial assignments of stereochemistry of juvabione and some of its analogues can be made on the basis of 13C nuclear magnetic resonance studies. The complete 13C n.m.r. spectral assignments for juvabione and five analogues are reported.
J(23)cis and J(23)trans of 2‐carbonyl substituted 2,3‐dihydrobenzofurans
Authors: Croce Piero Dalla , Stradi Riccardo 
Published: May 2005

AbstractThe J(23)cis and J(23)trans values in several 2‐carbonyl substituted 2,3‐dihydrobenzofurans were measured. Although J(cis)>J(trans), the values found disagree with the Karplus rule.
An instrumental modification for rapid‐scan deuterium magnetic resonance spectroscopy
Authors: Bloxsidge James P. 
Published: May 2005

AbstractA modification of a Bruker WH‐90 spectrometer is reported, enabling acquisition of rapid‐scan (Fourier transform correlation) deuterium magnetic resonance spectra, using the D‐lock frequency source and a computer generated field sweep. This modification is not suited to high sensitivity or high precision studies, but does avoid the considerable expense or extensive rebuilding required for a 19F lock channel and 2H pulsed Fourier channel.
Indirect 13C13C couplings in benzene and the contribution of their anisotropies to the direct couplings in the oriented molecule
Authors: Diehl P. , Bösiger H. , Jokisaari J. 
Published: May 2005

AbstractThe indirect ortho and para carbon‐carbon coupling constants in benzene were determined utilizing the deuterium isotope effect on the carbon chemical shifts in 1‐d1‐ and 1,3,5‐d3‐benzene. The measurements gave for J(CC, ortho) and J(CC, para) the values of 55.3 ± 0.5 Hz and 10.08 ± 0.10 Hz, respectively. The ratios of the direct dipolar CC coupling constants were calculated using the previous results of 1‐13C‐benzene in an oriented phase. These ratios differ from the theoretical ones obtained assuming the benzene ring to be hexagonal, showing significant indirect contributions in the D values.
Etude par RMN du 13C d'Hydroxy‐4 Coumarines Substituées en 3. Analyse par Corrélation des Effets de Substituants
Authors: Rabaron A. , Didry J.‐R. , Kirkiacharian B. S. , Plat M. M. 
Published: May 2005

AbstractLes déplacements chimiques du 13C et les constantes de couplage 13C‐1H d'hydroxy‐4 coumarines et d'hydroxy‐4 méthoxy‐7 coumarines substituées en 3 sont déterminés. Une corrélation à 3 paramètres: ℱ et ℛ de Swain et Lupton et Q de Schaefer appliquée à ces deux séries établit les relations linéaires qui permettent de prévoir les déplacements chimiques à partir des paramètres des substituants.
C,H coupling constants of propene
Authors: Dubs R. V. , Von Philipsborn W. 
Published: May 2005

AbstractThe proton coupled 13C NMR spectrum of propene has been analysed at 100.6 and 25.2 MHz and a complete set of C,H coupling constants is reported. In particular, vicinal and one‐bond coupling constants are discussed with respect to substituent effects of alkyl groups. An incremental method allows us to predict 1J(CH) in more highly methyl‐substituted alkenes.
Carbon‐13 NMR spectra of N‐methylimidazole‐substituted sterol esters
Authors: Wilk Manfred , Schmitt Karlheinz 
Published: May 2005

AbstractThe 13C NMR spectra of two N‐methylimidazole‐substituted sterol esters are discussed. The calculated shifts are compared to those obtained experimentally. For one of the sterol esters the experimental and calculated data show good agreement, and the substituent increments can be evaluated. This does not apply in the case of the second sterol ester, where the steric and/or electronic effects of a further substituent—a hydroperoxy group in close proximity to the N‐methylimidazole group—prohibits the additive calculation of substituent increments.
13C{1H} single frequency off‐resonance decoupling of secondary carbons
Authors: Roth Klaus , Bauer Hans 
Published: May 2005

Abstract13C{1H} single frequency off‐resonance decoupled spectra of secondary carbons with two chemically non‐equivalent protons are analysed theoretically and experimentally. By a careful analysis of the frequencies of all six transitions all spectral parameters, including the geminal proton‐proton coupling constant, can be determined very accurately.
Asymmetric NMR spectra of weakly coupled nuclei: A common characteristic in the 13C NMR spectra of [U‐13C]‐labeled molecules and in natural abundance protoncoupled 13C spectra
Authors: London R. E. , Walker T. E. 
Published: May 2005

AbstractTypically encountered proton‐decoupled spectra of [U‐13C]‐labeled molecules or proton‐coupled spectra of natural abundance or singly labeled molecules contain many nuclei which satisfy the weak coupling approximation. The spectra of such nuclei are frequently highly asymmetric and often appear to exhibit the skewed intensity distribution characteristic of strongly coupled spins. Analysis of typical cases indicates that such effects arise in the presence of at least one moderately strong coupling interaction in the spin system (Jδν ∼ 1/3), and the apparent intensity asymmetry reflects small differences in the spacing of unresolved components of the observed resonance. This effect is analogous to the case of ‘virtual coupling’ in which weakly coupled spins cannot be analyzed as first order spectra; however; the ABX spin system which generally serves as a model for such systems does not predict the existence of spectral asymmetry for the X resonances. Prediction of this asymmetry requires a spin system of at least four spins with at least ABMX complexity, and can be treated generally using the effective Hamiltonian approach of Poeple and Schaefer.
Assignment of stereochemistry to cyclohexenylidenecyanoacetates by 1H NMR spectroscopy
Authors: Bardakos Vassilios , Sandris Constantine 
Published: May 2005

AbstractThe stereochemistry of various pairs of isomeric 2‐cyclohexen‐1‐ylidenecyanoacetates was assigned using 1H NMR spectroscopy. The isomers with the γ‐methylene or the γ‐vinyl protons cis to the carbalkoxy group were found to have the signals of these protons at approximately 0.3 ppm and 1 ppm, respectively, downfield relative to their geometrical isomers or the corresponding 2‐cyclohexen‐1‐ylidenemalononitriles. The observation regarding the γ‐vinyl proton proved useful for the assignment of configuration to cyclohex‐enylidenecyanoacetates derived form cholest‐4‐en‐3‐one. The large and constant downfield shift (c. 1 ppm) of the γ‐vinyl proton when cis to the ester group results from the rigid cyclohexenylidenecyanoacetate system, in which the vinylic proton can approach more closely to the magnetically anisotropic ester carbonyl group.
15N chemical shifts and one bond 15N1H coupling constants in simple amides
Authors: Marchal J. P. , Canet D. 
Published: May 2005

AbstractAn indirect method is employed for determining the 15N parameters at the natural abundance level in a series of simple acyclic and cyclic amides. The one bond coupling constant, 1J(15N1H), and the 15N chemical shift are measured as a function of the carbonyl substituent group or the ring size and the nature of the solvent (CCl4 or H2O). These 15N parameters are related to the amide bond structure, the nitrogen configuration and possible intermolecular hydrogen bonding (amide‐amide or amide‐water).
Carbon‐13 nuclear magnetic resonance spectra. XVI—lanthanide induced signal shifts of diastereotopic 13C nuclei as a probe for a conformational equilibrium
Authors: Duddeck Helmut , Wiskamp Volker 
Published: May 2005

AbstractThe 13C NMR signals of the two methyl groups in 4‐hydroxy‐1‐isopropyl‐2‐oxaadamantane are anisochronous in the presence of Yb(fod)3. This is interpreted in terms of the different populations of three rotational conformers.
Stereochemical substructure codes for 13C spectral analysis
Authors: Gray N. A. B. , Nourse James G. , Crandell Christopher W. , Smith Dennis H. , Djerassi Carl 
Published: May 2005

AbstractComputer programs for encoding canonical representations of stereochemical substructural environments are presented. Applications of these substructure codes in the study of relationships between molecular structure and chemical shifts observed in 13C NMR spectra are described, using natural products as examples. The utility of the codes for the detection of erroneous spectral assignment is illustrated.
13C NMR spectroscopy of heteroaromatic compounds: A quantitative measure of electron deficiency and excessiveness
Authors: Paudler William W. , Jovanovic Misa V. 
Published: May 2005

AbstractA quantitative measure, πΔ, for expressing the π‐deficiency and π‐excessiveness of heteroaromatic compounds has been developed through 13C NMR chemical shift studies. An example which correlates electrophilic reactivity in π‐excessive systems with πΔ of these compounds is given. The following decreasing order of π‐excessiveness and increasing π‐deficiency of a number of heteroaromatic systems has been established (numbers in parentheses correspond to πΔ): tellurophene (1.83), selenophene (1.43), thiophene (1.35), furan (1.31), benzene (1.00), pyrazine (1.00) pyridine (0.89), pyrimidine (0.77), pyridazine (0.71), 1,2,4‐triazine (0.64). These correlations also allow the prediction of 13C chemical shifts in substituted heteroaromatic compounds, where the ratio of the difference between a given substituted heterocyclic compound and its parent, and the identically substituted benzene derivative, has been determined.
INDO calculations of the solvent dependence of some spin–spin couplings of fluorocarbons
Authors: Shargi S. N. , Webb G. A. 
Published: May 2005

AbstractThe results of some SCPT and SOS calculations of 1J(CH), 1J(FC), 2J(FH), 3J(FH), 3J(FF) and 1J(CC) in a variety of solvents are reported. The calculations employ the solvaton model and INDO parameters. In almost all cases the coupling is predicted to increase as the dielectric constant of the solvent increases, the exception being 3J(FH)cis in trifluoroethylene which is supported by experimental results.
13C NMR studies of some hydroxycoumarins and related compounds
Authors: Sankar S. S. , Gilbert R. D. , Fornes R. E. 
Published: May 2005

AbstractThe 13C chemical shifts and one‐bond carbon‐hydrogen coupling constants have been obtained for some hydroxycoumarins and their corresponding acetoxy and methoxy derivatives. The changes in the one‐bond carbon‐hydrogen coupling constants resulting from the conversion of a hydroxy group to an acetoxy group represent a simple method of assignment of the 13C NMR signals in coumarins which contain one or more hydroxy groups in the benzenoid ring.
Low‐frequency vibrational modes and temperature dependence of NQR frequencies in 1,2,4,5‐tetrabromobenzene
Authors: Rao N. Bharateswara , Rangacharyulu M. , Venkatacharyulu P. , Premaswarup D. 
Published: May 2005

AbstractA temperature variation study of the nuclear quadrupole resonance (NQR) frequencies for the two resonance lines in 1,2,4,5‐tetrabromobenzene was carried out in the range 77–300 K. The far‐infrared spectrum of 1,2,4,5‐tetrabromobenzene was recorded and the low‐frequency vibrational modes noted. From the nine observed frequencies, the torsional modes contributing to the change in NQR frequencies with temperature are identified by correlating the calculated values of the NQR frequencies at different temperatures with the observed values.
Determination of tautomeric phenotypes of β‐thioxo esters and characterization of the tautomeric enethiolic constituents by means of 13C NMR spectroscopy
Authors: Duus F. , Hansen P. E. 
Published: May 2005

AbstractThe 13C NMR spectra of 28 enethiolizable β‐thioxo esters and 6 enethiolizable β‐thioxo thioloesters have been recorded in order to establish the tautomeric phenotypes of these compounds. All compounds investigated are essentially enethiolic. The carbonyl‐conjugated (Z)‐enethiol form is the exclusive or predominant tautomer of open‐chain β‐thioxo esters and thioloesters, thioacylmalonates and medium‐sized 2‐alkoxycarbonylcycloalkanethiones. The carbonyl‐conjugated (E)‐enethiol form is identifiable for open‐chain α‐unsubstituted β‐thioxo esters and thioloesters, and abundant for open‐chain α‐substituted β‐thioxo esters. Non‐conjugated enethiol forms [i.e. (Z)‐ and (E)‐isomeric β,γ‐unsaturated β‐mercapto esters] are abundant tautomeric constituents of ω‐substituted and higher 2‐alkoxycarbonylcycloalkanethiones. The chemical shifts of the carbon atoms directly involved in the tautomeric change have been rationalized in terms of substituent screening contributions. Deuterium isotope effects on the central carbon atoms of selected deuterio‐enethiolic compounds have been measured in order to depict the ester group rotamerism in CO‐conjugated (Z)‐enethiols. The abundance of the CO‐conjugated (E)‐enethiols, as well as the preferred population of the non‐conjugated (Z)‐enethiol form relative to the non‐conjugated (E)‐enethiol form, is rationalized in terms of the occurrence of a no‐bond interaction between the lone‐pair electrons of the enethiolic sulphur atom and the ‘chelating’ methylene hydrogen atoms of cis‐alkyl groups.
Oxygen‐17 nuclear magnetic resonance study of some five‐membered heterocyclic derivatives
Authors: Chimichi Stefano , Nesi Rodolfo , De Sio Francesco 
Published: May 2005

Abstract17O NMR spectra have been obtained in the FT mode for some furan and isoxazole derivatives. The chemical shifts, mainly governed by the electronegativities of the atoms bonded to the central oxygen, are also affected by alkylation on the different positions of the ring systems, which gives rise to β and γ effects similar to those observed for simple aliphatic ethers.
1H and 13C NMR spectral assignments of isoquinuclidine‐3,5‐dione derivatives
Authors: Quirante Josefina , Diaba Faïza , Vila Xavier , Bonjoch Josep 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of six 5‐substituted 2‐azabicyclo[2.2.2]octane derivatives were fully assigned by COSY and HSQC experiments. Copyright © 2005 John Wiley & Sons, Ltd.
The turnover of phosphatidyl choline in rat cerebral cortex membranes in vivo
Authors: Lapetina E. G. , Lunt G. G. , De Robertis E. 
Published: May 2005

AbstractThe incorporation of [Me‐14] choline administered by intraventricular injection in vivo into the phosphatidyl choline of the membranes of rat cerebral cortex was studied, and it was demonstrated that the radioactive choline was incorporated almost exclusively into phosphatidyl choline in each of the fractions. The various membranous fractions had different half‐lives of phosphatidyl choline. The half‐life of the phosphatidyl choline of myelin was 167 days, the longest of any fraction, while the value of 27 days for mitochondria was the shortest. Phosphatidyl choline of microsomal membranes and synaptic vesicles had very similar half‐lives, whereas the purest fraction of nerve ending membranes gave a half‐life double that of synaptic vesicles.
Somal site of synthesis of fast transported materials in mammalian nerve fibers
Authors: Ochs S. , Sabri M. I. , Ranish N. 
Published: May 2005

AbstractThe crest of labelled materials carried down the fibers of cat sciatic nerve by the fast transport system was blocked by puromycin or cycloheximide injected into the lumbar 7th ganglion 20–30 min before the precursor 3H‐ leucine. The protein synthesis blocking agents were less effective when given 5 min after 3H‐leucine injection and ineffective when injected 20 min or more afterwards. Differential centrifugation of the labelled components of nerve showed a relatively high specific activity (counts/min/mg protein) present in the small particulate and supernatant fractions of nerves removed 5–6 hrs after ganglion injection. Sephadex G‐200 column gel filtration of the supernatant fraction showed the presence of labelled soluble proteins with molecular weights of 450,000 (peak Ia) and 68,000 (peak Ib), polypeptides with a molecular weight of 5,000, and a small amount of free leucine (peak II). In nerves taken 16–22 hrs after ganglion injection, a relatively greater specific activity was found in the peak Ia soluble protein. Labelled materials carried down by fast transport were allowed to enter the axons for a period of 5–6 hrs, and then further outflow from the somas prevented by ligations made just distal to the ganglia. After an additional 16 hrs in the animal it was found that the polypeptides and free leucine, which had entered these nerve fibers earlier, were not then later synthesized into the higher molecular weight proteins characteristic of the later downflows. These studies show a rapid synthesis of labelled materials carried down the fiber by the fast transport system and a translocation in the somas of another portion, mainly protein which is then carried out into the axon at later times.
Parametric studies of the response decrement produced by mechanical stimuli in the protozoan, Stentor coeruleus
Authors: Wood David C. 
Published: May 2005

AbstractA decrement in the probability of eliciting a response is observed during the course of repetitive stimulation in many response systems of both metazoa and protozoa. Those forms of metazoan response decrement called habituation have recently been characterized behaviorally. In the studies reported here, the response decrement of the contractile protozoan, Stentor coeruleus, to repeated mechanical stimulation was systemically characterized to provide a comparison with metazoan habituation. This change in response probability was closely approximated by a negative exponential function after the first few stimuli. Animals responded to parametric variations of stimulus amplitude, interstimulus interval and retention period in a manner paralleling that observed in metazoa. However, neither interpolated large amplitude mechanical stimuli nor suprathreshold electrical stimuli produced dishabituation in Stentor though these stimuli are among the most effective dishabituating stimuli for metazoan tactile response systems. Behavioral analysis of the response decrement proceeded on the assumption that Stentor contains receptor and effector mechanisms only. Since the response decrement was not correlated with a change in responsiveness to electrical stimuli, the ability of the animal to contract appears to be unaltered by the process producing the response decrement. On the other hand, weak mechanical prestimuli were found to increase the rate of the response decrement which suggests that a process of receptor adaption is operative.