bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chromatographic evaluation of chiral (1R‐trans)‐N, N′ ‐1,2‐cyclohexylenebisbenzamide‐oligodimethylsiloxane copolymeric stationary phases for capillary supercritical fluid chromatography
Authors: Petersson Patrik , Markides Karin E. , Johnson Deborah F. , Rossiter Bryant E. , Bradshaw Jerald S. , Lee Milton L. 
Published: May 2005

AbstractA novel approach to the design of chiral stationary phases (CSPs) is illustrated by the synthesis and evaluation of selective and efficient copolymeric CSPs with alternating chiral (1R‐trans)‐N, N′‐1,2‐cyclohexylenebisbenzamide and achiral (oligodimethylsiloxane) blocks. These materials are shown to resolve a variety of chiral diols. Evaluation of the performance of one of these phases in GC and SFC suggests that SFC can produce higher resolution because of its lower operating temperature which facilitates solute‐stationary phase interactions. The influence of different chiral (position of substitution) and achiral (chain length) blocks of the copolymer on solute retention, efficiency, chiral selectivity, and resolution were studied, as well as the reproducibility of the column preparation method.
Molecular formula determination of halogenated compounds in environmental samples using gas chromatography and atomic emission dection
Authors: Pedersen‐Bjergaard Stig , Asp Tone Normann , Vedde John , Greibrokk Tyge 
Published: May 2005

AbstractAtomic emission spectroscopy coupled with capillary gas chromatography (GC) has been evaluated for molecular formula determination of several chlorinated and brominated compounds present in three environmental samples. Variations in elemental responses due to compound type, poor chromatographic resolution, and small signals relative to the background were all found to complicate molecular formula calculations. About 20% of the calculated molecular formulas presented in this paper agreed with theoretical values. For most applications, identifications based solely on GC coupled with theoretical values. For most applications, identifications based solely on GC coupled with atomic emission detection (AED) are not sufficiently accurate. However, the combination of elemental information derived form a GC‐AED analysis with complementary data obtained from other detection techniques results in a strong analytical tool for analyte identification.
Nitrogen‐15 NMR characterization of 7‐methylguanosine and its base‐pair with cytidine in dimethyl sulphoxide
Authors: Barbarella G. , Bertoluzza A. , Tugnoli V. 
Published: May 2005

AbstractThe neutral and the protonated, positively charged, forms of 7‐methylguanosine have been characterized by 15N NMR in dimethyl sulphoxide. It is shown that in this solvent protonated 7‐methylguanosine gives specific interactions with cytidine at the same sites as those involved in the guanosine‐cytidine Watson‐Crick base‐pairs present in nucleic acids.
NMR studies of indoles and their N‐carboalkoxy derivatives
Authors: Morales‐Ríos M. S. , Joseph‐Nathan P. 
Published: May 2005

AbstractThe 13C NMR assignment of indoles and 5‐methoxyindoles substituted at position 3, and some of their N‐carboalkoxy derivatives, was achieved from one‐ and two‐dimensional NMR experiments. Substituent chemical shifts and 1 J(CH) values were evaluated. The dynamic processes of N‐carboalkoxyindoles and N‐carboalkoxyindoline observed by high‐field 1H NMR show the existence of two preferred rotamers around the carbamate NC(O)OR bond, which was interpreted in terms of frequency/field strength‐dependent phenomena.
Cycloaddition reactions of cephalosporin compounds. IX—1H and 13C NMR stereochemical study of the 1,3‐dipolar cycloadditions of diazoalkanes to 2‐methylenecephem derivatives
Authors: Cs. Jászberény J. , Pitlik J. , Batta Gy. , Kövér K. E. , Kollár K. 
Published: May 2005

AbstractA series of known and novel 2‐methylenecephem derivatives were prepared and their reactions with diazomethane, phenyldiazomethane and diphenyldiazomethane were studied. The initially formed 1‐pyrazolino derivatives easily underwent spontaneous loss of nitrogen, leading to 2‐spirocyclopropylcephems. The two reaction products, formed in a 3:1 to 8:1 ratio on addition of diphenyldiazomethane, were separated by column chromatography and distinguished by their 1H and 13C NMR spectra. The 1H NMR spectra did not exclude the possibility of 1‐pyrazoline formation, but elemental analysis and 13C data corroborated the previous assumption that loss of nitrogen took place, even in those cases when it did not occur during the reaction.
Dynamic NMR study of the electronic state of heteroaromatics. III—Pyrylium salts or intramolecularly bridged pentamethine cyanines?
Authors: Kleinpeter E. , Spitzner R. , Schroth W. , Pihlaja K. , Mattinen J. 
Published: May 2005

AbstractThe 13C NMR spectra and the temperature‐dependent 1H NMR spectra of a series of NR2‐substituted pyridines and pyrones were studied, and the 13C chemical shifts and the rotational barriers about the exocyclic partial C,N double bonds were compared with the corresponding values for suitable pyridinium, pyrylium and thiopyrylium salts. The NMR spectroscopic results are discussed in the light of the electronic state and mesomerism in the species studied; the salts in question should be named, from the electronic point of view, more realistically as bridged pentamethine cyanines rather than pyridinium, pyrylium and thiopyrylium salts.
Conformations in solution of four 2,4,5,7‐tetramethyloctane‐4,5‐dicarboxylates: Molecular mechanics and NMR studies
Authors: Holland Kelvyn A. , Rae Ian D. , Weigold Josephine A. 
Published: May 2005

AbstractPotential energy calculations (MM2), low‐temperature 1H and 13C NMR spectra and 1H–1H COSY spectra are reported for four octane derivatives, the central portions of which constitute tetrasubstituted succinates. The existence of several conformers differing in stereochemistry in this central moiety is predicted by calculations and observed in low‐temperature NMR. The periphery of each molecule is in an extended configuration, as shown by the existence of long‐range (W‐plan) couplings involving the methyl groups.
Aza crown ethers. 13C and 1H NMR studies of ring conformations and stereochemically dependent shifts in N‐substituted dibenzodiaza‐18‐crown‐6 ethers and a nine‐membered analog
Authors: Buchanan G. W. , Landry D. J. 
Published: May 2005

AbstractRemarkably large (> 10 ppm) 13C NMR chemical shift differences are observed in solution and in the solid phase between ortho aromatic carbons of structurally analogous dibenzodiaza‐18‐crown‐6 ethers and their 9‐membered ring counterparts. On the basis of geometries deduced from 1H1H NOESY results, the upfield 13C chemical shifts in the 18‐membered systems are attributed to cis coplanar interactions between the terminal carbons of these torsional networks. Overall mobilities of 9‐ and 18‐membered ring systems are examined via 13C spin–lattice relaxation times.
γgaucheEffects in the 1H and 13C NMR spectra of steroids. II
Authors: Hammann P. E. , Kluge H. , Habermehl G. G. 
Published: May 2005

AbstractγgaucheEffects of 17β‐ and 7α‐substituted 14α‐steroids were studied by 1H and 13C NMR spectroscopy. A linear correlation was found between the 1H chemical shift of H‐12β and the 13C chemical shift of C‐12 for C‐17β‐substituted steroids and between the chemical shifts of H‐14α and C‐14 in C‐7α‐substituted compounds.
An NMR study of the hydroxylamine‐induced denitration of nitrocellulose, nitroamylose and some model monosaccharide nitrate esters
Authors: Bulusu S. , Axenrod T. , Liang B. , Yuan L. 
Published: May 2005

AbstractThe previously known method of partial denitration of trinitrocellulose by hydroxylamine in pyridine was further investigated by NMR and applied to trinitroamylose and several other monosaccharide nitrates to study its selectivity. The sites of denitration were determined in each case using 13C and 15N NMR and, in most cases, by 2D homo‐ and hetero‐nuclear (15NOC1H and 13C1H) chemical shift correlations. The results indicate that denitration of the polysaccharide nitrates is a highly regiospecific reaction occurring at the 2‐position only, whereas with the monosaccharide nitrates denitration takes place with less selectivity, at the 4‐position predominantly, and to a lesser extent at the 3‐position.
13C NMR spectra of multifunctional bile acid derivatives
Authors: Blossey Erich C. , Ford Warren T. , Periyasamy Mookkan 
Published: May 2005

AbstractCarbon‐13 NMR signals were assigned to a set of methyl 5β‐cholanoates having multiple functional groups, including hydroxy, carbonyl and acetoxy groups. Assignments were based on empirical chemical shift rules for α‐, β‐ and γ‐substituent effects, direct spectral comparison with compounds of similar structure, DEPT and 2D‐HETCOR. Use of β‐substituent effects permitted the assignment of structural changes at positions 3, 7 and 12 of the steroidal nucleus.
Carbon‐13 chemical shift anisotropies of solid amino acids
Authors: Ye Chaohui , Fu Riqiang , Hu Jianzhi , Hou Lei , Ding Shangwu 
Published: May 2005

AbstractAn approach to spinning sideband (SSB) separation of protonated and non‐protonated carbons in slow spinning conditions via dipolar dephasing is proposed. This method offers two features: SSB spectral simplification, which greatly reduces the overlaps encountered in a usual SSB spectrum, and spectral distinction of overlapped resonances for protonated and non‐protonated carbons. The 13C chemical shift anisotropies of the 20 amino acids as polycrystalline powdered solids were completely measured with the SSB intensity analyses as an application of the suggested approach.
Application of Hahn‐echo extended pulse sequences to phosphorus–nitrogen compounds. Determination of coupling signs and detection of 15N31P15N isotopomers in natural abundance
Authors: Wrackmeyer Bernd , Köhler Christian , Kupče Eriks 
Published: May 2005

AbstractHahn‐echo extended (HEED) pulse sequences in one‐ and two‐dimensional experiments were successfully applied to phosphorus–nitrogen compounds with two PN bonds {2‐chloro‐1,3‐dimethyl‐1,3,2‐diazaphospholidine (1), 2‐tert‐butyl‐1,3‐dimethyl‐1,3,2‐dizaphospholidine (2), bis(diethylamino)chlorophosphane (3) and bis(diethylamino)phosphenium cation (4; counterion [AlCl4]−)}. In the case of 2, the 31P resonance signal was detected as a sharp triplet for the 15N31P15N isotopomer in natural abundance: the secondary isotope effect on the coupling constant 1J(31P15N) in 14N31P15N and 15N31P15N isotopomers is < 0.05 Hz; the isotope‐induced shifts 1Δ 15/14N(31P) are additive. The value of 1Δ 15/14N(31P) in the phosphenium cation 4 is markedly more negative than that in its precursor 3 or other aminophosphanes. For 2, the absolute signs of the coupling constants 2J(15N 1H) ( < 0), all 3J(31P1H) ( > 0), 1J(31PC13C) ( < 0), 2J(31PC13C) ( > 0), 2J(31PN 13CCH3) ( > 0) and 2J(31PNCCH2) ( < 0) were determined using 1H detected 2D inverse pseudo triple resonance 1H{(13C)31P} experiments and 2D 13C1H, 15N1H and 31P1H heteronuclear shift correlations.
NMR assignments for 6‐hydroxy‐2‐methyl‐2‐(4‐methylpent‐3‐enyl)‐2H‐1‐benzopyran (cordiachromen A)
Authors: Kim In Kyu , Park Sun Ku , Erickson Karen L. 
Published: May 2005

Abstract6‐Hydroxy‐2‐methyl‐2‐(4‐methylpent‐3‐enyl)‐2H‐1‐benzopyran, a fairly common naturally occurring terpene hydroquinone, was isolated from the Korean ascidian Aplidium multiplicatium and its 1H and 13C NMR assignments were made and/or corrected from earlier literature values.
Dérivés Alléniques du Phosphore. Influence de l'État de Coordination du Phosphore et de la Nature des Radicaux Liés au Phosphore sur les Signes de J(PH)
Authors: Simonnin Marie‐Paule , Charrier Claude , Lecourt Marie‐José 
Published: May 2005

AbstractLes signes des constantes de couplage phosphore‐proton dans les dérivés alléniques du phosphore ont été déterminés soit par analyse des spectres de type AB2X, soit par Double Résonance, et les signes absolus probables ont été obtenus en supposant que 3J(PH) est toujours positif.Dans les oxydes de phosphines alléniques, les signes sont les suivants: 2J(PH) +, 3J(PH) +, 4J(PH) −, 5J(PH) + et 4J(PH) dépend principalement des effets inducteurs des radicaux liés au phosphore.Dans les phosphines alléniques, les signes sont: 2J(PH) +, 3J(PH) +, 4J(PH) − et + et 4J(PH) dépend à la fois des effets inducteurs et de résonance des radicaux liés au phosphore: ce couplage, normalement négatif, deviant positif lorsque le phosphore porte des substituants donneurs par effet de résonance.Ces résultats sont interprétés par l'existence d'une liaison pπdπ dans les phosphines.
The NMR spectra and conformations of cyclic compounds–III: The conformations of some pinane derivatives
Authors: Abraham R. J. , Bottom F. H. , Cooper M. A. , Salmon J. R. , Whittaker D. 
Published: May 2005

AbstractThe 220 MHz 1H spectra of isoverbanone, nopinone and verbanone are reported.The spectra of the first two are completely assigned but that of verbanone only partially. The coupling constants obtained provide information about the conformation of these molecules. The isoverbanone molecule is almost Y shaped, but that of nopinone is between a Y shape and a half‐chair conformation with the six membered ring bent away form the gem dimethyl groups. These conformations are consistent with the known steric interactions in these molecules.
Applications of proton magnetic resonance spectroscopy to structural problems–XXXI Hindered internal rotation in 2‐dimethyl‐aminopyridine derivatives
Authors: Katritzky A. R. , Tiddy G. J. T. 
Published: May 2005

AbstractΔH‡ and ΔS‡ values for the restricted rotation of the dimethylamino groups in 5‐nitro‐and 3,5‐dinitro‐2‐dimethylaminopyridine and 4‐dimethylaminopyrimidine are reported and discussed.
Deceptive simplicity in NMR spectra of oriented molecules
Authors: Diehl P. , Khetrapal C. L. , Lienhard U. 
Published: May 2005

AbstractThe theory for deceptive simplicity in the NMR spectra of oriented molecules is discussed in terms of degeneracy of subspectra. The conditions for the degeneracy of AB, AB2 and AA′BB′ spectra leading to deceptive simplicity in the spectra of the type ABX, AB2X, AA′BB′X and AA′XX′ are reported.It is shown that the conditions for deceptive simplicity are easily fulfilled for ABX, AA′BB′X and AA′XX′ cases. It is further demonstrated that deceptive simplicity is not so common in AB2X spectra.The proton spectra of partially oriented 2,4,5‐trichloronitrobenzene (AB) and 2,6‐dibromo‐pyridine (AB2) are use to illustrate degeneracy and those of p‐chloro‐ and p‐bromo‐fluorobenzenes are reported to demonstrate deceptive simplicity.
A proton magnetic resonance study of complexes of pyridine, 2‐methylpyridine 3‐methylpyridine, 4‐methylpyridine, and 2,6‐dimethylpyridine with borane and boron trifluoride
Authors: Fratiello Anthony , Schuster Ronald E. 
Published: May 2005

AbstractA variable temperature, proton magnetic resonance study has been made of complexes of pyridine, 2‐methylpyridine, 3‐methylpyridine, 4‐methylpyridine, and 2,6‐dimethylpyridine with borane and boron trifluoride. By lowering the temperature and slowing ligand exchange, separate resonance signals can be observed for bulk and complexed molecules of the base. A direct comparison of the complexing abilities of these ligands was made by studying them in pairs with borane or boron trifluoride. The complexing abilities, as estimated from the NMR data, decreased in the order: 4‐MePy > 3‐MePy > Py > 2‐MePy > 2,6‐MePy. This trend was interpreted in terms of steric effects and the basic strengths of these molecules towards boron trifluoride.
The proton magnetic resonance spectra of cyclopentadiene trimers at 220 MHz
Authors: Foster R. G. , McIvor M. C. 
Published: May 2005

AbstractDetailed interpretations of the spectra of four of the possible isomeric cyclopentadiene trimers are given. It is shown that the geometry of the ring fusion can be determined by measuring the chemical shifts of the bridge protons and of the allylic proton on the cyclopentene ring 3a‐H.
Carbon‐proton coupling constants in α‐chlorostyrene‐α‐13C
Authors: Servis Kenneth L. , Casanova Joseph , Geisel Manfred 
Published: May 2005

AbstractThe two stereochemically distinct two‐bond carbon‐13‐ hydrogen coupling constants J(13CCH), for α‐chlorostyrene‐α‐13C have been shown to be of similar magnitude but opposite sign (−6.3 and +5.6 Hz). A simple additivity relationship which adequately reproduces all the reported J(13CCH) values for chloroethylenes has been found.
Etudes par RMN en serie heterocyclique–III. Non‐equivalence magnetique et inversion de l'azote dans une serie d'heteocycles pentagonaux diazotes, pyrazolines‐2 et 3, pyrazolidines et pyrazolidones
Authors: Elguero J. , Marzin C. , Tizané D. 
Published: May 2005

AbstractLa non‐équivalence de groupements éthyle, benzyle et isopropyle fixés sur les azotes de pyrazolines‐2 et 3, de pyrazolidines et de pyrazolidones est fonction de l'asymétrie existant dans la molécule. Celle‐ci peut provenir soit d'un carbone du cycle, soit de l'un des azotes rendu asymétrique par protonation, quaternarisation ou simplement par ralentissement de son inversion, Ce dernier phénomène n'a été observé que dans le cas des pyrazolidines (possibilité d'inversion de deux azotes adjacents) et des pyrazolidones (inversion de l'azote non amidique): il est fonction des substitutions et des variations de température.
The 19F chemical shift in oxygen containing carbon fluorine products
Authors: Ciampelli F. , Venturi M. Tacchi , Sianesi D. 
Published: May 2005

AbstractWe have examined the 19F NMR spectra of a number of oxygen‐containing fluorocarbon products and obtained a comprehensive set of 19F chemical shift values, which enabled us to determine the influence of an oxygen atom bonded to a fluorocarbon group on the 19F chemical shift. The influence of neighbouring fluorocarbon groups, either directly connected or separated by an oxygen atom, was also considered.Our results may be summarized as follows. An oxygen atom bonded by a single bond (ether type bond) to a fluorine substituted carbon atom decreases the 19F chemical shift, as does the introduction of a further fluorine atom. Considering two adjacent fluorocarbon groups, a variation of x ppm in the 19F chemical shift of one of the two groups gives a variation of 0·12 x ppm in the opposite sense on the 19F chemical shift of the other group. If the two groups are connected by an ether oxygen atom, the effect is only about 0·06 x ppm.
On the nuclear magnetic resonance spectrum of reduced nicotinamide adenine dinucleotide
Authors: Hollis Donald P. 
Published: May 2005

AbstractThe two C‐4 protons of reduced nicotinamide adenine dinucleotide (NADH) produce an AB NMR spectrum at 100 MHz as well as at 220 MHz. This observation allows an upper limit of 50 sec−1 to be placed on the mean rate of interconversion of the two folded forms of NADH invoked to account for the magnetic non‐equivalence of the C‐4 protons. The interpretation of non‐equivalence of the C‐4 protons in terms of the various equilibria among folded and unfolded forms of NADH and its possible significance in the mechanism of action of dehydrogenase enzymes is discussed. It is suggested that one folded form of NADH is strongly favored thermodynamically over the other and that the resulting magnetic non‐equivalence of the C‐4 protons is of doubtful significance in explaining the stereospecificity of dehydrogenase enzymes toward the nicotinamide ring.
Nuclear magnetic resonance studies of 5,6‐dicarboxy‐2‐norbornene derivatives
Authors: Kamezawa Norimasa , Sakashita Kiyoshi , Hayamizu Kikuko 
Published: May 2005

AbstractA detailed study has been made on the 1H nuclear magnetic resonance (NMR) spectra of 5,6‐dicarboxy‐2‐norbornene derivatives, whose chemical shifts and geminal, vicinal and long‐range spin‐spin coupling constants were determined. Each signal of the spectra of these derivatives shows a slight low‐field shifts compared with norbornene itself. In the case of five methyl esters studied in this work, the signal of the 7s‐proton remains at approximately the same position in all the compounds, but that of the 7a‐proton is more variable. For the chemical shifts of the 7a‐proton of the five methyl esters, an additive rule seems to hold: that the magnitude of the low‐field shift, from the 7a‐signal of norbornene itself, is obtained by adding each of the effects of the carboxyl and the carbomethoxy groups substituted at the endo‐5‐(or 6‐) or the exo‐5‐(or 6‐) positions of the norbornene ring. In most of the derivatives considered in this work, the spin‐spin coupling constants, except those between bridgehead and bridged methylene protons, are about 1 to 2 Hz smaller than those of many other norbornene derivatives already studied. This fact seems to suggest that norbornenes, which have two bulky adjacent substituents at 5‐ and 6‐positions, may suffer distortions in the norbornene ring.
Die Kernresonanzspektren von N‐substituierten 2.6‐Dimethylmorpholinen
Authors: Brügel W. 
Published: May 2005

AbstractDie NMR‐Spektren von am N substituirten 2.6‐Dimethylmorpholinen warden nach gaschromatographischer Trennung der Stereoisomren aufgenommen. Die spektralen Parameter warden daraus durch eine mathematische Analyse erthakten. Auf bisher ungklärte Besonderheiten der Spektren der cis‐Isomeren wird hingewiesen. Die Differenz der chemischen Verschiebung der 3‐ständigen Protonen der cis‐Isomeren erweist sich stark von dem N‐Substituenten abhängig.
Protonenresonanz‐Spektroskopie Ungesättigter Ringsysteme—XIV: Zur Frage der Substituenten‐Einflüsse auf die Resonanzfrequenzen und Vicinalen Kopplungskonstanten von protonen in substituierten Benzolen
Authors: Bremser Wolfgang , Günther Harald 
Published: May 2005

AbstractDer Einfluß von Substituenten auf die Protonenresonanzen und die vicinalen H, H‐Kopplungskonstanten in Benzolderivaten wird mit Hilfe linearer Ausgleichsrechnungen untersucht. Für die relativ zur Protonenresonanz des Benzols auftretende Abschirmungsänderung Δσ bei der Substitution wird die Beziehung

angegeben, die eine Berechnung der Substituenten‐Effektes mit Hilfe des dipolaren und quadratischen Feldeffektes (Ez, E2) und der π‐Ladungsdichte‐Änderung am benachbarten C‐Atom (Δρ) erlaubt.Die vicinalen Kopplungskonstanten lassen sich mit der HMO‐π‐Bindungsordnung nicht korrelieren. Eine Ausgleichsrechnung unter Benutzung der bekannten Abhängigkeit der Kopplung von der Substituenten‐Elektronegativität liefert

wobei ΔEα und ΔEβ die durch Substitution bedingte Änderung der Elektronegativität in α‐ bzw. β‐Stellung zum betrachteten HCCH‐Fragment bedeuten.
Interpretation of NMR spectra from four‐membered rings
Authors: Whipple Earl B. , Evanega George R. 
Published: May 2005

AbstractWhen as many as four vicinal couplings occur between four protons situated on three carbon atoms of a cyclobutane ring, one can employ the Karplus relation to assign the configuration of substituents at the remaining positions and make some inferences about the stereochemistry. Four examples are described; the spectra and data are analyzed.
Zur Kenntnis der NMR‐Daten der O2CCH2S‐Gruppe
Authors: Brink M. , Larsson E. 
Published: May 2005

AbstractDie magnetische Nichtäquivalenz der Methylenprotonen in den Verbindungen HO2CCH2SR′ und RO2CCH2SR′ wurde untersucht und die Einwirkung der Substituenten auf die geminalen Kopplungskonstanten JAB diskitiert. Es zeigte sich, dass die geminalen Kopplungskonstanten der Methylenprotonen fast unabhängig von der Konstitution der Verbindugen und den verwendeten Lösungsmitteln waren. Die magnetische Nichtäquivalenz der Methylenprotonen war sowohl von der Konstitution wie vom Lösungsmittel abhängig.