bluuebunny/crossref_metadata_2025_split huggingface dataset:
Separation and characterization of components of peptide libraries using on‐flow coupled HPLC—NMR spectroscopy
Authors: Lindon J. C. , Farrant R. D. , Sanderson P. N. , Doyle P. M. , Gough S. L. , Spraul M. , Hofmann M. , Nicholson J. K. 
Published: May 2005

AbstractThe efficiency of directly coupled HPLC—NMR spectroscopy for the separation and characterization of synthetic peptide libraries was investigated using a model system based on a mixture of all 27 tripeptide combinations of alanine (A), methionine (M) and tyrosine (Y) as the C‐terminal amides. The 1H NMR spectra were obtained in real time using on‐flow HPLC—NMR spectroscopy at 600 MHz and 21 of the 27 peptides were identified on the basis of chemical shifts and coupling constants, including the use of diagnostic values derived from 1H NMR spectra and 1H13C and 1H15N HMQC studies on authentic AAAOH and YYYOH. The effects on 1H NMR chemical shifts of pH and of varying proportions of acetonitrile and water as occurred during the gradient elution HPLC run were evaluated. The HPLC—NMR approach could provide a facile method for investigating the relative efficiency of resin‐based peptide synthesis for different amino acid combinations and should rapidly provide data suitable for deriving structure‐retention time relationships for peptides.
Structural assignment of the intramolecular meta photocycloadduct isomers from 4‐phenoxybut‐1‐enes and 3‐benzyloxyprop‐1‐enes by proton NMR spectroscopy
Authors: Blakemore D. C. , Gilbert A. , De Bruyn A. , De Keukeleire D. , Van der Eycken E. 
Published: May 2005

Abstract1H NMR data (400 and 500 MHz) are reported for the intramolecular meta photocycloaddition products from 4‐phenoxybut‐1‐enes and 3‐benzyloxyprop‐1‐enes. The structures of these photoproducts, and in particular the discrimination between the 1,6‐ and 7,8‐bridged isomers, are deduced from COSY 45 and 60 experiments and spin‐decoupling techniques.
13C NMR study of some sulphur‐containing 5‐trifluoromethylpolychloro‐pyridines
Authors: Sveshnikov Nikolay N. , Sipyagin Alexey M. , Dobrokhotova Olga V. 
Published: May 2005

AbstractA 13C NMR study of a series of novel 2,4‐thio‐substituted 5‐trifluoromethylpoly‐chloropyridines was carried out. The carbon chemical shifts and external long‐range 13C, 19F NMR coupling constants between the pyridine ring carbons and the trifluoromethyl group are reported.
Héterocycles contenant du phosphore—XVII: Etude par Résonance Magnétique Nucléaire et analyse conformationnelle de quelques oxazaphosphorinanes‐1,3,2
Authors: Durrieu Josiane , Kraemer Raymond , Navech Jacques 
Published: May 2005

AbstractLe spectre de RMP de quelques nouveaux oxazaphosphorinanes‐1,3,2 est analysé. Dans un cas, après élimination du couplage entre les protons et le phosphore, on a affaire à un système ABKLXY particulier dans lequel certaines constantes de couplage entre protons vicinaux sont nulles. Le système ABKLXY où JAK = JAL = JBK = JBL est étudié, ce qui permet d'accéder à la plupart des paramètres du composé considéré. La conformation du cycle est précisée, la valeur de l'enthalpie libre conformationnelle est donnée et, pour l'oxazaphosphorinane‐1,3,2 précédent, l'angle de torsion des liaisons C4C5 et C5C6 est calculé.
NMR studies on the interaction of methylaluminium compounds with some methyl‐substituted pyridines
Authors: Wakatsuki Kizuku , Matsubayashi Gen‐etsu , Tanaka Toshio 
Published: May 2005

AbstractThe interactions of trimethylaluminium and dimethylaluminium chloride with some methyl‐substituted pyridines have been investigated in dichloromethane by means of temperature‐dependent proton NMR spectra. 4‐Methylpyridine forms 1:1 addition complexes with trimethylaluminium and dimethylaluminium chloride. 2,6‐Dimethyl‐ and 2,4,6‐trimethylpyridines have been found to yield three types of complex with dimethylaluminium chloride, however, and only one type of complex with trimethylaluminium. The configurations of the complexes in solution, and exchange equilibria between methylaluminium compounds and 2,6‐dimethylpyridine are also discussed.
An indo investigation of magnetic resonance constants of azaaromatic systems
Authors: Galasso V. 
Published: May 2005

AbstractINDO–MO calculations have been performed on the ESR hyperfine coupling constants of the pyridinyl radical and the radical anions of pyrimidine, quinoline, isoquinoline, acridine and benzcinnoline. The nuclear spin coupling constants and the 14N nuclear quadrupole coupling constant of pyridine have also been calculated. In general, calculated values are in satisfactory agreement with the experimental data.
Ionen. X—Das Tetraphenyloborat‐Ion als Hilfsmittel bei Diastereotopie‐Problemen
Authors: Schiemenz G. P. , Klemm P. 
Published: May 2005

Abstract[B(C6H5)4]⊖ ist ein leistungsfähiges NMR‐Verschiebungsreagens für Aminosulfonium‐Kationen. In einem Beispiel zeigen diastereotope Protonen unter normalen Meßbedingungen (Chlorid in CDCl3) keine Anisochronie. Diese wird durch einen Solvenseffekt sichtbar, jedoch nur in einem Maße, das die geminale Kopplungskonstante und die wahren Signallagen noch nicht zu ermitteln gestattet. [B(C6H5)4]⊖ erzeugt jedoch annähernd ein Spektrum erster Ordnung, dem alle Parameter glatt entnommen werden können. Die Daten helfen im Chlorid‐Spektrum sehr schwache Signale aufzuspüren und das Ausmaß der Anisochronie festzustellen. Salzmischungen legen verdeckte Signale frei.
Carbon‐13 nuclear magnetic resonance spectroscopy: VIII—aliphatic hydrocarbon derivatives
Authors: Miyajima Goh , Nishimoto Kichisuke 
Published: May 2005

AbstractCarbon‐13 NMR chemical shifts of several series of aliphatic hydrocarbon derivatives–‐substituted methanes, ethanes, isopropanes, n‐propanes and n‐butanes–‐were found to have a linear relationship with σ‐electron densities (Qσ) calculated by the method of σ‐included ω‐HMO. A plot of the 13C NMR chemical shift of a given carbon in a substituted propane versus that of the corresponding carbon in a substituted butane showed a good linearity with a slope of unity. The values of the 13C chemical shifts of the n‐butyl derivatives converged rapidly to a constant value as the distance from the substituent increased. Accordingly, the value for the δ‐carbon was found to be constant regardless of the substituent. These results show that the 13C NMR chemical shifts of aliphatic hydrocarbon derivatives are mainly dependent on inductive effects. The convergence shown by the experimental results is supported by the calculated results of the Qσ values of the n‐butyl derivatives.
Calculation of gauche coupling constants from substituent electronegativities
Authors: Forrest T. P. 
Published: May 2005

AbstractThe calculation of gauche coupling constants from substituent electronegativities by a method which takes into account the orientation of the substituents is described. This correlation has been derived from the coupling constants of disubstituted ethanes and has been applied to the calculation of coupling constants in cyclohexanes and 6‐membered heterocycles. The detection of angular distortion in 6‐membered rings from the difference between calculated and observed coupling constants is also described.
The 19F NMR spectrum of cis‐1,2‐dichlorohexafluorocyclobutane
Authors: Gazzard Valerie J. , Harris Robin K. 
Published: May 2005

AbstractThe 19F spectrum of cis‐1,2‐dichlorohexafluorocyclobutane has been fully analysed on the basis of an [ABX]2 spin system, with initial treatment at an [AMX]2 level. The chemical shift and coupling constants are presented, and the latter are discussed. Some comments are made on the spectrum of the trans isomer.
Mise en evidence de plusieurs processus d'échange intramoléculaire dans les iodures de bis(méthyl thio)‐1,1 dialkyl iminio‐3 propène substitués ou non en 2 et 3
Authors: le Botlan Denis , Filleux‐Blanchard Marie‐Louise , le Coustumer Gérard , Mollier Yves 
Published: May 2005

AbstractUne étude RMN des sels d'iminium de formule générale a été réalisée à diverses températures.
13C FT‐NMR spectra of alkyl substituted furans. A study of the influence of steric interactions
Authors: Kiewiet A. , de Wit J. , Weringa W. D. 
Published: May 2005

AbstractThe 13C FT‐NMR spectra of thirteen furans, monodi‐ or trisubstituted with methyl and/or t‐butyl groups, were studied in detail. Substituent effects of methyl and t‐butyl groups on the chemical shifts of ring carbon atoms are additive in nonsterically hindered furans. Steric shifts for the ring carbon atoms are found in furans with bulky neighbouring substituents, but the hybridisation of the carbon atoms in these hindered furans is not changed. The chemical shifts of the substituents are calculated according to the Grant‐Cheney formula. No simple relationship between steric shift and steric hindrance can be ascertained.
Conformational studies by nuclear magnetic resonance. VII—The direct observation of rotational isomers in some enamino carbonyl compounds and their thione derivatives by carbon magnetic resonance
Authors: Da̧browski Janusz , Kamieńska‐Trela Krystyna , Kozerski Lech 
Published: May 2005

AbstractCarbon‐13 magnetic resonance spectra of the s‐cis and s‐trans rotamers of enamino ketones and thiones of the general formula
\documentclass{article}\pagestyle{empty}\begin{document}${\rm X =}\mathop {\rm C}\limits^{\rm 1} {\rm (}\mathop {\rm R}\limits^{\rm 1} {\rm)}\mathop {\rm C}\limits^{\rm 2} {\rm H =}\mathop {\rm C}\limits^{\rm 3} {\rm HN}\mathop {{\rm R}_{\rm 2}}\limits^{\rm 4}$\end{document} (where × = O or S and R‐1, R‐4 = alkyl) have been obtained. With dimethylaminoacrolein and its thione analogue, restricted rotation could only be observed in the latter. The chemical shift differences between rotamers and homologues are attributed to changes in conjugation and to induced bond polarisation, both these factors resulting from steric strain. In particular, nonplanar deformations of the s‐trans rotamers are deduced from their C‐2 chemical shift values.
Photodimers of cinnamic acid and related compounds. A stereochemical study by NMR
Authors: Montaudo G. , Caccamese S. , Librando V. 
Published: May 2005

Abstract1H NMR spectra of photodimers of cinnamic acid, chalcone and related compounds were analysed, and the spectral parameters and all the coupling constants were obtained. A clear differentiation among the head‐to‐head and head‐to‐tail stereoisomers can be obtained by considering the values of K, L, M and N parameters. The different types of hh and ht isomers can be immediately assigned by considering the relative values of the three‐bond couplings. An authentic example of an A2B2 spin system is reported.
Carbon‐13 spin‐lattice relaxation times and nuclear overhauser enhancements in some simple fluorocarbons
Authors: Hawkes Geoffrey E. , Abraham Raymond J. 
Published: May 2005

AbstractCarbon‐13 spin‐lattice relaxation times (T1) and 13C‐{19F} nuclear Overhauser enhancement (NOE) factors have been measured for some simple fluorocarbons by pulse‐Fourier transform methods—‘progressive saturation’ and ‘dynamic Overhauser enhancement’. The NOE factors are shown to be large for 13C with directly bonded fluorines, and the values for T1 and the NOE factors are similar to those obtained elsewhere on the corresponding hydrocarbons.
Evidence from fluorine and proton NMR spectra for restricted rotation about the PO bond in some steroidal phosphorofluoridates
Authors: Cooper G. H. , Chittenden Rosemary A. 
Published: May 2005

AbstractThe salient features of the 19F and 1H NMR spectra of seven steroidal phosphorofluoridates are presented and evidence for restricted rotation, obtained from high temperature studies and deuteration experiments, is discussed.
The proton exchange reaction between indene and the indenyl anion
Authors: Vos H. W. , Bakker Y. W. , Velthorst N. H. , Maclean C. 
Published: May 2005

AbstractThe proton exchange reaction between the indenyl carbanion and its parent compound indene has been studied by NMR as a function of temperature. The rate of this bimolecular reaction is very low and has been found to be strongly dependent on the polarity of the solvent. In solvents like dimethoxyethane (ϵ = 7·2) and diglyme the reaction becomes manifest in the NMR spectrum only at elevated temperatures (T > 150°C). In hexamethylphosphortriamide (ϵ = 30) the rate is much greater and line broadening may be observable at room temperature. The reaction in this solvent is characterised by a frequency factor f = 7 × 107 1 mol−1 s−1, an activation enthalpy ΔH ≠ = 9·5 kcal mol−1 and an entropy of activation ΔS≠ = −23 e.u. The low reaction rate and its solvent dependence are briefly discussed.
Analysis of the 1H NMR spectrum of α‐tetralone
Authors: Gatto Karen , Reinheimer John D. , Shafer Kenneth , Gerig J. T. 
Published: May 2005

AbstractAn analysis of both the aromatic and aliphatic portions of the 1H NMR spectrum of α‐tetralone has been carried out. Two deuterated derivatives, 2,2‐dideuterio‐ and 4,4‐dideuterio‐α‐tetralone, were prepared to facilitate unambiguous assignment of chemical shifts for the aliphatic protons. The conformation of the 6‐membered alicyclic ring of the molecule is defined by the coupling constants among the aliphatic protons. Benzylic coupling was the only detectable long range interaction between the aliphatic and aromatic protons of the molecule. The magnitude and sign of these coupling constants agree with previous calculations of Wasylishen and Schaefer.
A carbon‐13 NMR study of some sulfur‐containing organic compounds
Authors: DeSimone Richard E. , Albright Michael J. , Kennedy William J. , Ochrymowycz Leo A. 
Published: May 2005

AbstractCarbon‐13 NMR spectra have been obtained and analyzed for a series of saturated linear and cyclic sulfur‐containing organic molecules. For the large cyclic polythiaethers whose proton spectra are broad and unresolved, it is found that carbon‐13 spectra are sharp and well resolved. The resonances of all carbons fall within the expected chemical shift ranges. Based upon the comparative resolution in the spectra of large and small cyclic species, it is concluded that whatever conformational motion may exist within the rings must be occurring very rapidly on the NMR time scale.
The determination of conformational effects in some fluorobenzenes by a combined mo/coupling constant treatment
Authors: Abraham Raymond J. , Busby James F. , Cooper M. Ashley , Roe Anthony M. 
Published: May 2005

AbstractThe correlation of JmetaFF in some 1‐substituted‐2,6‐difluorobenzenes (1) with the bond order matrix of the fluorine 2p(π) orbitals provides information on the orientation of the substituents and the position of the counter‐ion in the anilinium salt. The calculated charge densities in the analogous anilinium fluoride ion pair are compared with those of the free ion and neutral molecule.
13C NMR studies: XLVI—rearrangements and deuterium exchange via homoenolization in bicyclooctanones. A convenient preparation of bicyclic β,γ‐ and γ,δ‐unsaturated ketones
Authors: Hudyma D. M. , Stothers J. B. , Tan C. T. 
Published: May 2005

AbstractWith t‐BuO−/t‐BuOH at 185°C bicyclo‐[2.2.2] and ‐[3.2.1]octanones are interconvertible. In saturated systems equilibrium is attained very slowly, but in unsaturated cases an equilibrium mixture heavily favoring the [3.2.1] skeleton is obtained relatively rapidly, thereby providing a convenient route to homo and bis‐homo conjugated ketones. Experiments in t‐BuOD using 13C NMR to monitor deuterium incorporation revealed five major sites of exchange in the unsaturated ketones.
13C13C coupling constants and substituent effects on 13C chemical shifts in 13C labelled pyrene and pyrene derivatives
Authors: Hansen P. E. , Poulsen O. K. , Berg A. 
Published: May 2005

AbstractLong range inter‐ring 13C13C couplings are found to be effective in the title compounds, and the magnitudes of coupling constants and of substituent effects on 13C chemical shifts, as well as the signs of the latter, alternate with respect to the number of connecting bonds.
Hindered rotation of the dimethylamino and dimethylthioamide groups in two ortho substituted N,N‐dimethylthiobenzamides
Authors: Lozac'h R. , Legrand L. , Sandström J. 
Published: May 2005

AbstractHindered rotation in two o‐substituted N,N‐dimethylthiobenzamides was investigated by variable temperature 1H NMR spectroscopy. For one compound, the enthalpies and entropies of activation for (i) thioamide group rotation around the ArC bond and (ii) dimethylamino group rotation around the CN bond were obtained by full line shape analysis; a possible coupling between the two processes is discussed. A new simple method has also been applied to the analysis of dimethylamino exchange and results are in complete agreement with the full line shape analysis with somewhat better precision.
NMR studies on σ‐adducts of heterocyclic systems with nucleophiles. VI—Carbon‐13 nuclear magnetic resonance investigations on σ‐adduct formation of pyrimidine and some of its derivatives with potassium amide in liquid ammonia
Authors: Geerts J. P. , van der Plas H. C. , van Veldhuizen A. 
Published: May 2005

AbstractCarbon‐13 NMR spectra of the σ‐adduct complexes formed in liquid ammonia between the amide ion and some 2‐R‐pyrimidines, some 4‐chloro‐2‐R‐pyrimidines (R = dimethylamino‐, N‐methylanilino, piperidino‐, morpholino‐, phenyl‐), 5‐bromo‐2‐piperidinopyrimidine and pyrimidine itself are described, together with the carbon‐13 NMR spectra of the anions formed by amino‐proton abstraction resulting from the reaction of the amide ion with 2‐anilino‐4‐chloro‐, 4‐chloro‐2‐methylamino‐, 2‐anilino‐ and 2‐methylaminopyrimidine in liquid ammonia. Additionally, the carbon‐13 NMR spectra of the parent compounds of the anionic σ‐adducts and anions, and that of 4‐chloropyrimidine, were recorded in CDCl3.
Mutual assignment of subspectra and substructures—A way to structure elucidation by 13C NMR spectroscopy
Authors: Bremser W. , Klier M. , Meyer E. 
Published: May 2005

AbstractA novel approach to utilising digital computers and a collection of reference data for the interpretation of 13CNMR spectra is outlined. Because of the almost unlimited possibilities of molecular structures in organic chemistry, a matching of subspectra with substructures seems most appropriate, followed by an iterative confirmation of the suggested structures. For this purpose the possibility of a search for structure increments and the accompanying chemical shifts is provided by linking the spectroscopic and structural information using a formulae reading machine and generating the topological connectivity table. Three practical examples demonstrate the application of this set of programs and some of the experiences gained during operation.
Mechanism of serine protease action. Ionization behavior of tetrahedral adduct between α‐lytic protease and tripeptide aldehyde studied by carbon‐13 magnetic resonance
Authors: Hunkapiller Michael W. , Smallcombe Stephen H. , Richards John H. 
Published: May 2005

AbstractMagnetic resonance techniques have been used to study the ionization behavior of the catalytic triad of the serine protease, α‐lytic protease, in the tetrahedral, hemiacetal complex it forms with the aldehyde inhibitor, N‐ac‐L‐ala‐L‐pro‐L‐alaninal. Chemical shift, coupling constant and relaxation measurements of a carbon‐13 nucleus specifically incorporated in C‐2 of the imidazole ring of the single histidine residue of the protein show that, above pH 7, the imidazole ring of the catalytic triad in the enzyme + aldehyde complex is neutral. We suggest, further, that a neutral carboxylic acid group for Asp 102 and an oxyanion for the hemiacetal are most likely to describe the state of ionization of the other groups above pH 7. Around pH 6·25, both the oxyanion and the histidine become protonated in a co‐operative process which forces the histidine away from its rigidly localized position as a member of the catalytic triad into a solution‐like environment.
13C‐NMR‐Spektroskopie von Cyclopropenonen und Cyclopropenyliumionen (Cyclopropenonchemie: VII)
Authors: Dehmlow Eckehard V. , Zeisberg Reinhard , Dehmlow Sigrid S. 
Published: May 2005

AbstractDie 13C‐NMR‐Spektren von dreizehn Cyclopropenonen, zwei Cyclopropenthionen, fünf zugehöriger Cyclopropenyliumsalze und von drei Cyclobutendionen werden tabelliert und diskutiert.
Silicon‐29 and carbon‐13 NMR studies of organosilicon chemistry. II—The Methylethoxysilanes MenSi(OEt)4−n
Authors: Harris Robin K. , Kimber Barry J. 
Published: May 2005

AbstractSilicon‐29, carbon‐13 and oxygen‐17 NMR data are reported for the methylethoxysilanes, MenSi(OEt)4−n with n = C to 3. The values of 1J(SiC) vary greatly, in a manner which appears to be inconsistent with an effect of s‐character variation alone. The chemical shifts are discussed in terms of possible π‐bonding. Silicon‐29 and carbon‐13 spin‐lattice relaxation times and nuclear Overhauser effects are also reported and discussed.
Carbon‐13 NMR spectra of all‐trans‐N‐retinylidene‐n‐butylamine as an analogue of the Schiff's base linkage‐compound in visual pigment
Authors: Tokitô Yasuo , Inoue Yoshio , Chûjô Riichirô , Miyoshi Yasuhiro 
Published: May 2005

AbstractCarbon‐13 NMR spectra have been obtained for all‐trans‐N‐retinylidene‐n‐butylamine as an analogue of the Schiff's base linkage compound in visual pigment. The chemical shift changes on going from all‐trans‐retinal1 to all‐trans‐N‐retinylidene‐n‐butylamine are observed. These changes indicate the collapse of the bond alternation in conjugated polyene carbons, whereas N‐protonation in all‐trans‐N‐retinylidene‐n‐butylamine does not affect the bond alternation.
Carbon‐13 NMR spectroscopy of the biological pigments luteoskyrin and rugulosin and some polyhydroxyanthraquinone analogues
Authors: Toma F. , Bouhet J. C. , Van Choung P. Pham , Fromageot P. , Haar W. , Rüterjans H. , Maurer W. 
Published: May 2005

AbstractThe bianthraquinonic biological pigments luteoskyrin and rugulosin and five polyhydroxyanthraquinone derivatives are studied by carbon‐13 NMR in DMSO solution. Peak assignment for the fourteen carbon atoms of these compounds is achieved by proton spin decoupling and by investigating the effect of ionisation of the hydroxyl groups upon the carbon chemical shifts. Carbon chemical shifts in the planar hydroxyanthraquinones can be rationalised in terms of conjugation and intramolecular hydrogen bonding. The latter is responsible for the relative acidity of the hydroxyl groups in the analogues, and for the different conformations proposed for luteoskyrin and rugulosin. Tautomeric equilibria occur in DMSO and water–DMSO solutions for the anionic species [LS]2− and [RG]2−. This can account for the binding of luteoskyrin and rugulosin to nucleic acids.
RMN du carbone‐13 en serie cyclopropanique. Effets de substituants
Authors: Monti J. P. , Faure R. , Vincent E. J. 
Published: May 2005

AbstractLes effets de substituants sur les déplacements chimiques de dérivés cyclopropaniques ont été étudiés par RMN du carbone‐13. Les déplacements chimiques théoriques de cyclopropanes trisubstitués sont en bon accord avec les valeurs expérimentales lorsqu'on introduit dans les corrélations des paramètres d'interaction du second ordre.
The structure of pyrazine determined from its proton magnetic resonance spectrum, including the carbon‐13 satellites
Authors: Diehl P. , Bösiger H. , Tracey A. S. , Ader R. 
Published: May 2005

AbstractThe structure of pyrazine partially oriented in a liquid crystal has been determined from its proton magnetic resonance spectrum utilising the 13C satellites (at natural abundance). Carbon–carbon, carbon‐hydrogen and hydrogen–hydrogen internuclear distance ratios have been determined.
1H and 31P NMR spectra of substituted methylphosphonic acids with indirect determination of 31P shifts
Authors: Rueppel M. L. , Marvel J. T. 
Published: May 2005

AbstractProton and phosphorus magnetic resonance spectra of substituted methylphosphonic acids have been determined as a function of pH. A method has been developed for measuring the 31P shift indirectly by optimal heteronuclear decoupling of the 1H spectra of samples and standards. Control experiments have demonstrated the broad applicability of this technique to the characterization of low milligram samples of N‐phosphonomethylglycine and potential metabolites.