bluuebunny/crossref_metadata_2025_split huggingface dataset:
High‐resolution 13C NMR studies of solid 1,4‐bis(n‐butylamino)anthraquinone
Authors: Harris R. K. , Jonsen P. , Packer K. J. 
Published: May 2005

AbstractHigh‐resolution 13C NMR spectra of solid 1,4‐bis(n‐butylamino)anthraquinone are presented. In spectra measured at 22.6 MHz the effects of two short‐range and two long‐range residual (13C, 14N) dipolar couplings have been observed. Only the short‐range effects are observable in the 50.3 MHz spectra. These typical asymmetric doublets allow the determination of the 14N nuclear quadrupole coupling constant (χ=e2Qq/h=−3.0 MHz), the asymmetry parameter (η=0.3) and the orientation of the electric field gradient tensor of the 14N in the molecular framework.
Ring finger testing in carpal tunnel syndrome: A comparative study of diagnostic utility
Authors: Uncini Antonino , Lange Dale J. , Solomon Murray , Soliven Betty , Meer Jacob , Lovelace Robert E. 
Published: May 2005

AbstractBecause digit 4 (D4) has dual innervation, median and ulnar sensory latencies can be determined over identical distances. To determine if D4 testing is more sensitive than other commonly used techniques to diagnose carpal tunnel syndrome (CTS), we examined 42 hands with clinical evidence of carpal tunnel syndrome and 43 control hands. D4 latency was significantly longer than controls more often than digit 2 (D2) in patients with CTS. Comparing median to ulnar latencies from D4 was the most sensitive method to make the diagnosis of CTS. in mild CTS, a characteristic double peak potential was seen in recordings from the median nerve after stimulating D4. This potential provided immediate visual confirmation of the diagnosis of CTS. Comparing D4 latency along median and ulnar nerves is useful for detecting mild CTS and should be used whenever there are clinical signs and symptoms of CTS but electrodiagnostic studies are normal or borderline.
Proton and carbon‐13 nuclear magnetic resonance studies of substituted pyridines and pyrimidines: VII—The structure of hydroxy‐ and mercapto‐ pyridines and pyrimides from J(HH) and J(CH) values
Authors: Vitorge M. C. , Chenon M. T. , Coupry C. , Lumbroso‐Bader N. 
Published: May 2005

AbstractAccurate values of iJ(HH) and iJ(CH) were obtained for a series of hydroxy‐and mercaptopyridines and‐pyrimidines. It is shown that the 3J(CH) values provide a valuable criterion for differentiating aromatic from quinoidal structures, and is an easy method for determining N‐methylation or N‐addition sites.
Long‐range shielding by cyclopropyl groups in 10‐spirocyclopropyl‐9,10‐dihydroanthracenes
Authors: Ryder Mary T. , Rosenfeld Stuart M. 
Published: May 2005

AbstractThe peri protons in a series of 10‐spiroclopropyl‐9,10‐dihydroanthracenes have been shown to have shifts consistent with large (0.43‐0.55 ppm) long‐range shielding effects exerted by neighboring cyclopropyl groups. The shieldings are expected to be sensitive to variations in preferred conformation and, since the range of observed shifts for the five compounds studied is relatively small, it is concluded that all exhibit similar conformational preference.
NMR evidence for planar chirality in natural porphyrins
Authors: Gaudemer A. , Gaudemer F. , Merienne C. 
Published: May 2005

AbstractThe 1H NMR spectra of several six‐coordinate cobalt(III) porphyrins of general formula L2Co(DPDME)CI, where DPDME=deuteroporphyrin dimethyl ester and L is an optically active ligand, have been measured at 250 or 400 MHz. In a few cases, two signals of equal intensity are observed for the L ligand protons. This magnetic non‐equivalence, which never exceeds 0.04 ppm, is thought to arise from the planar chirality of the porphyrin ring, which makes a proton in the ligand L above the porphyrin ring and the corresponding proton below this ring diastereotopic.
17O NMR spectra of equatorial and axial hydroxycyclohexanes and 5‐hydroxy‐1,3‐dioxanes and their methyl ethers
Authors: Eliel Ernest L. , Liu Kwang‐ting , Chandrasekaran Subramanian 
Published: May 2005

Abstract17O chemical shifts of axial hydroxyl groups in cyclohexanols are upfield of those of corresponding equatorial groups, but in 5‐hydroxy‐1,3‐dioxanes the opposite is observed: the axial OH resonates downfield of the equatorial OH. The situation is the same in the corresponding methyl ethers and is, thus, not a result of intramolecular hydrogen bonding in the axial 5‐hydroxy‐1,3‐dioxane, but appears to parallel the effect on 13C and 19F shifts observed in corresponding equatorial and axial 5‐methyl‐ and 5‐fluoro‐1,3‐dioxanes, which has been attributed to an upfield shifting effect of the antiperiplanar γ‐located heteroatoms. Surprisingly, the reciprocal effect is not seen in the ring 17O shifts of the 5‐hydroxy‐1,3‐dioxanes. A δ compression shift is seen in the 17O spectrum of trans‐3,3,5‐trimethylcyclohexanol (syn‐axial OH and CH3), analogous to the effect earlier reported in 13C spectra. Conversion of four of the alcohols to methyl ethers produces a large upfield effect on the 17O shift, larger in the cyclohexanols than in the 1,3‐dioxane‐5‐ols. Similar upfield shifts have been recorded in the literature; their extent depends on whether the alcohols are primary, secondary or tertiary.
ESR and ENDOR studies on a 5‐O‐membered crown ether bearing a triphenylmethyl moiety
Authors: Tajima Kunihiko , Shimizu Hiroaki , Morita Takaaki , Tomoda Hideyuki , Mukai Kazuo , Ishizu Kazuhiko 
Published: May 2005

AbstractA new 5‐O‐membered crown ether spin‐labelled with a triphenylmethyl group was prepared. The intramolecular unpaired π‐electron delocalization was investigated by ENDOR. The ENDOR of the crown methylene group adjacent to the aromatic ring revealed non‐equivalence in the magnitude of the proton hyperfine splittings. Based on the temperature‐dependent ENDOR line separation, the activation energy of the conformational change of the methylene protons was estimated. Upon metal chelation into the crown ring the dissociation of the dimer to the monomer radical was greatly affected, and an increase in the activation energy of the vibrating methylene protons was detected.
13C NMR spectra and structure of mono‐, di‐ and trimethoxyphenylethylamines and amphetamines
Authors: Bailey Keith , Legault Donald 
Published: May 2005

AbstractCarbon‐13 and proton chemical shifts of mono‐, di‐ and trimethoxylated phenylethylamines (PEAs) and their hydrochlorides were determined and the signals were assigned and are reported. The data are interpreted to indicate that the side‐chains of PEA derivatives and amphetamine salts have the amino and aromatic moieties predominantlytrans(antiperiplanar), that ‘sandwiched’ OCH3groups and side‐chains are forced out of the ring plane and that planarortho‐OCH3groups have their electron lone pairs oriented toward the side‐chain and partially stabilizegaucherotamers. It is suggested that the location and density of electronic charges just outside the aromatic ring will significantly affect interactions with putative receptors.
Phosphol‐3‐ene 1‐oxides and ‐sulfides. A systematic investigation via carbon‐13 nuclear magnetic resonance spectroscopy
Authors: Buchanan G. W. , Webb V. L. 
Published: May 2005

Abstract13C NMR chemical shifts and 13C31P couplings are reported for 18 phosphol‐3‐ene 1‐oxides and 18 corresponding sulfides. The effects of methyl substitution at positions 3 and 4 on the carbon shifts have been systematically explored and substituent parameters derived. One bond couplings from phosphorus to C‐2 and C‐5 have been related to the sum of the exocyclic substituent group electronegativities (covalent boundary potential values).
Nuclear magnetic resonance of phosphorus compounds: 9—The NMR spectra of phosphirane
Authors: Goldwhite Harold , Rowsell David , Vertal Lawrence E. , Bowers Michael T. , Cooper M. Ashley , Manatt Stanley L. 
Published: May 2005

AbstractThe 100 MHz proton and 40.4 MHz 31P NMR spectra of phosphirane (1) have been recorded at −20 °C and analysed iteratively to yield coupling constants and chemical shifts. The 22.6 MHz 13C spectrum of 1 was recorded at 0 °C and analyzed. The 31P chemical shift of 1 was measured as 40 467 515.97 ± 0.08 Hz relative to TMS as 100 000 000.00 Hz. The geminal P‐C‐H couplings in 1 are opposite in sign and of different magnitudes (+16.14 and −2.64 Hz); the PH coupling (+158.34 Hz) is smaller than that in any other organic phosphine. These observations are discussed and correlated with the geometry of 1. The electronic structure of the strained ring of 1 is discussed in terms of a localized valence bond approach.
Selective INEPT, a new technique for the13C NMR assignment of methylene carbons with non‐equivalent protons, and its application to the analysis of the13C NMR spectrum of monensin
Authors: Furihata Kazuo , Seto Haruo , Ohuchi Muneki , Otake Noboru 
Published: May 2005

AbstractA new method based on the combination of selective proton decoupling and INEPT is explained in detail. This technique, named selective INEPT (SEL‐INEPT), is a useful and sensitive method for the13C NMR assignment of methylene carbons with non‐equivalent protons. The13C NMR spectrum of monensin has been analysed by the application of this technique.
Stereochemistry of organic sulphur compounds: 12—Configurational assignment of 2‐methylsulphinyl‐1‐phenylethanol and some O‐derivatives
Authors: Brunet Ernesto , Gracía‐Ruano José L. , Hoyos Miguel A. , Rodríguez Jesús H. , Prados Pilar , Alcudia Felipe 
Published: May 2005

AbstractThe conformational analysis of the diastereomeric 2‐methylsulphinyl‐1‐phenylethanol and its O‐methyl and O‐acetyl derivatives has been performed by 1H NMR spectroscopy. The study of the influence of dilution and solvent polarity changes on the coupling constants has permitted the configurational assignment of each diastereoisomer. The role played by hydrogen bonding in the hydroxysulphoxides has also been studied by IR spectroscopy.
Anisochrony of isopropyl methyl groups in 1‐isopropyl‐substituted tetralins and indans
Authors: Pourahmady N. , Palaniswamy V. A. , Eisenbraun E. J. 
Published: May 2005

Abstract1‐Isopropyl‐5‐methylindan, 1‐isopropyl‐7‐methylindan and 1‐isopropyl‐1,2,3,4‐tetrahydronaphthalene show a large anisochrony (magnctic non‐equivalence) of the isopropyl methyl signals at room temperature in their1H NMR spectra. A decrease in magnitude of this anisochrony is observed, in each case, in the temperature range 30‐150 °C. However, for 1‐isopropyl‐8‐methyltetralin, the magnitude of the non‐equivalence of the isopropyl methyl signals is unexpectedly small. These latter signals converge at 85 °C and then diverge in the opposite direction over the range 85‐150 °C. This alteration in anisochrony with temperature change for all cases is observed as a continuous downfield migration of one signal which, in turn, results from variations in conformation populations.
The mass spectra of 1‐arylanthra‐9,10‐quinones
Authors: Buckle D. R. , Waight E. S. 
Published: May 2005

AbstractThe mass spectra of 1‐phenylanthra‐9,10‐quinone and 20 substituted l‐phenylanthraquinones having alkyl methoxyl, nitro and halogen substituents in the o‐, m‐ and p‐positions of the phenyl ring have been measured. The spectra are discussed with particular reference to the loss from the molecular ion of a hydrogen atom and of the substituent.
Fluorinated tropylium ions in the mass spectra of some polyfluoroaromatic compounds
Authors: Bruce M. I. , Thomas Mair A. 
Published: May 2005

AbstractThe most prominent ion in the mass spectra of C6F5CH2X (X  H, Br, CH:CH2, COCl, and CH2C6F5) is C7F5H2+, formulated as the pentafluorotropylium cation. This ion is also found, in an amount comparable to the parent ion, in the spectrum of (C6F5)2CH2. The heptafluorotropylium cation is found similarly in the spectrum of C6F5CF3. The mass spectra of (C6F5)2CHBr and [(C6H5)2CH]2 exhibit an ion C13F10H+ as the base peak, which is probably a pentafluorophenylpentafluorotropylium cation.The alcohol (C6F5)2CHOH shows loss of C6F5, followed by 2H, as a major breakdown pathway.The mode of formation, and the subsequent fragmentation, of the major ions in these spectra, are discussed.
A study of rearrangement processes in the mass spectra of substituted diphenyl‐ethers
Authors: Ballantine J. A. , Pillinger C. T. 
Published: May 2005

AbstractAn investigation of the mass spectra of a number of substituted diphenyl ethers has shown that the major fragment ions are commonly due to cleavage of the molecule into the two benzene ‘half’ fragments although in many cases the molecular ion is the most abundant species observed.Little evidence is seen of MCO or MCHO peaks in these molecules but a large number of different rearrangement processes have been observed which involve ortho‐substituents. These rearrangement ions, although in some cases not very abundant, can be diagnostic in the problem of locating substituents in the diphenyl ether nucleus.
Derivatives of cyclotetrazenoborane (tetrazoborol‐2‐ine)—VI.1 Mass spectra of B substituted cyclotetrazenoboranes
Authors: Brittain E. F. H. , Leach J. B. , Morris J. H. 
Published: May 2005

AbstractThe mass spectra of B substituted 2,5‐dimethyl cyclotetrazenoboranes have been studied. The compounds Me2N4BD, Me2N4BEt, Me2N4BVi, Me2N4BCl and Me2N4BBr give confirmatory evidence that loss of N2+H. from the system occurs by loss of H from the side chain and that the BR bond is very stable under electron impact conditions. Fragmentation proceeds in a similar fashion to that of the 2,5‐dimethyl substituted compounds with H bonded to the boron atom.
Chemistry of lichen constituents—VI: Mass spectra of usnic acid, lichexanthone and their derivatives
Authors: Letcher R. M. 
Published: May 2005

AbstractThe mass spectra of usnic acid, decarbousnic acid, usnetic acid and usnetol are reported and mechanistically interpreted. The mass spectra of lichexanthone and lichexanthone methyl ether were also examined, and the unusal features of the latter spectrum have been rationalized.
Electron‐impact studies of organometallic molecules—X. Some simple transition metal fluorocarbon complexes
Authors: Bruce M. I. 
Published: May 2005

AbstractThe mass spectra of several fluoroalkyl, fluoroalkenyl and fluoroacyl complexes of manganese, rhenium, iron and ruthenium carbonyls are described. After loss of carbonyl groups, fluoroalkyl compounds eliminate an olefin, with formation of metal halide species. A trifluorovinyl complex shows a novel elimination of a carbon atom to give an ion postulated to be a difluorocarbene‐metal fluoride; the occurrence of difluorocarbene‐metal ions in the spectra of some related complexes is also discussed. The spectra of the acyl complexes show little evidence of elimination of the acyl carbonyl group; the major process is fission of the CORf bond with loss of a fluoroalkyl radical and formation of the cationic metal carbonyl, e.g. π‐C5H5M(CO)3+ (M  Fe or Ru). The relevance of thermal or photochemical model reactions to processes occurring in the mass spectrometer is discussed.
The mass spectra of some methyl norbornyl chlorides
Authors: Bunton C. A. , Del Pesco T. W. 
Published: May 2005

AbstractThe mass spectra of exo‐2‐norbornyl chloride, 1‐ and 2‐methyl exo‐2‐norbornyl, exo‐camphenilyl, apoisobornyl, bornyl and isobornyl chloride, and camphene hydrochloride, α‐ and β‐fenchyl chloride and fenchene hydrochloride, and exo‐isofenchyl chloride and 2,5,5‐trimethyl exo‐2‐norbornylchloride, and camphene and α‐fenchene have been examined at 12 to 16 and 80° eV and at 30 to 49 and 80°, or higher temperatures. Wagner‐Meerwein rearrangements occur very readily in the ion source and compounds related by these rearrangements give very similar fragmentation patterns. Thermal decompositions are important with the tertiary chlorides especially at higher source temperatures. The rates of methanolysis of some of these chlorides were measured.
Massenspektrometrischer Zerfall und Umlagerung von α‐Trifluoracetaminocarbonium‐Ionen
Authors: Prox A. , Schmid J. 
Published: May 2005

Abstractα‐Trifluoracetaminocarbonium‐Ionen treten als charakteristische Bruchstücke in den massenspektren von N‐Trifluoracetyl‐α‐aminosäuren und deren Derivaten auf. Sie zerfallen unter Eliminierung stabiler Neutralmolekeln, wobei in erster LInie die Struktur ihres Substituenten entscheidenden Einfluß ausübt. Im Zuge dieser Fragmentierungen kommt es bei einer Reihe von Ionen zu bemerkenswerten Strukturumlagerungen.
Massenspektrometrischer Zerfall und Umlagerung von α‐substituierten N‐Methyl‐benzylamiden
Authors: Prox A. , Schmid J. 
Published: May 2005

AbstractDer massenspektrometrische Zerfall einiger α‐substituierter N‐Methylbenzylamide mit verschiedenen N‐Acylgruppen wird anhand der Ergebnisse aus hochauflösender Massenbestimmung, Berechnung der metastabilen Ionen Untersuchung spezifisch deuterierter Verbindungen diskutitert. Dabei wird die Strukturumlagerung der durch α‐Spaltung entstandenen N‐Methyl‐α‐acylaminocarboniu‐Ionen nachgewiesen. Sie ist von der Art der N‐Acylgruppe abhängig. In den Massenspektren von N‐Acetyl‐bzw. N‐p‐Cl‐Benzoyl‐methyl‐α‐phenyläthylamid wird die Wanderung der α‐Methylgruppen beobachtet.
Mass spectra of some alkyl isoxazoles
Authors: Ohashi Mamoru , Kamachi Hajime , Kakisawa Hiroshi , Tatematsu Akira , Yoshizumi Hideo , Kano Hideo , Nakata Hisao 
Published: May 2005

AbstractThe mass spectra of several compounds obtained during the process of Stork's isoxazole synthesis9 as well as the related isoxazoles have been investigated. The fragmentations of simple alkyl isoxazoles are nicely formulated via azirine intermediates. A striking difference between the spectra of isoxazoles and those of methylfurans as to the relative abundance of [M — l] peaks is noteworthy. The very low abundance of these peaks in the former reflects the unique character of isoxazole nucleus due to the preferential cleavage of NO linkage rather than a benzylic CH bond rupture. If an alkyl substituent is present at 4‐position in 3,5‐dimethylisoxazoles, strong peaks at m/e 110, 68 and 43 are common in their spectra. The analyses of metastable transitions and high resolution measurements have demonstrated that the formation of these ions can be interpreted by a mechanism involving the cleavage of NO linkage.
The ions [CH3S]+, [C2H5S]+ and [CH3O]+ formed by electron‐impact
Authors: Amos D. , Gillis R. G. , Occolowitz J. L. , Pisani J. F. 
Published: May 2005

AbstractThe mass spectra of deuterated species shows that both the isomeric ions [CH2SH]+ and [CH3S]+ are formed in the ratio 2:1 from CH3SH; the ions [CH3CHSH]+ and [CH3CH2S]+ in the ratio 0·8:1 from CH3CH2SH; and [CH2OH]+ and [CH3O]+ in the ratio 6·7:1 from methanol.The heats of formation of [CH3S]+ and [C2H5S]+ are of the order of 222 and 203 Kcal.mole−1 respectively. The isomeric ions cannot be distinguished on thermodynamic grounds.
Organic ions in the gas phase—XXI: Synthesis and mass spectra of deuteriothiophenes
Authors: Meyerson Seymour , Fields E. K. 
Published: May 2005

AbstractMass‐spectral and n.m.r. analysis of thiophenes labeled by exchange with deuteriosulfuric acid establishes that exchange at the 2 and 5 positions is essentially complete before any deuterium is incorporated at positions 3 and 4. Thus, such exchange is a satisfactory procedure for position‐specific labeling. Mass spectra of the labeled thiophenes show that about 60% of the [CHS]+ ion yield is derived from molecular ions that have not undergone prior rearrangement. The remaining 40% arises by a path or paths in which the four hydrogen atoms lose position identity. Other decomposition paths contributing to the mass spectrum are characterized by more nearly complete scrambling of hydrogens.
Mass spectrometric studies of structural isomers—II: Mono‐and bicyclic C6H10 molecules
Authors: Winters Robert E. , Collins Jerome H. 
Published: May 2005

AbstractThe electron‐impact‐induced ionization and fragmentation of six C6H10 structural isomers have been studied in order to determine the effect of isomerism upon their mass spectrometric behavior. The 70 eV mass spectra, metastable transitions and appearance potentials of the principal ions are reported. Significant differences between the mass spectra of the six isomers were observed; however, metastable transition and appearance potential data indicate that the fragmentation path‐ways are the same for all the C6H10 molecules. Experimentally determined ionization potentials for the structural isomers are presented and compared to ionization potentials calculated by the bond orbital method. Utilizing fragmentation pathways deduced from general features in the mass spectra and from observed metastable transitions, we calculated heats of formation (ΔHf) for the observed principal ions and compared these values to ΔHf values for isomeric ions from other molecules.
Mass spectrometry of methyltetrazoles
Authors: Forkey D. M. , Carpenter W. R. 
Published: May 2005

AbstractThe mass spectra of tetrazole, all isomers of monomethyl‐ and dimethyltetrazole, several trifluoromethyl substituted tetrazoles, as well as deuterated analogs, were recorded. Loss of N2 was the important fragmentation of the molecular ions of tetrazole and 2‐methyl substituted tetrazoles; however, HN2 loss was more important for 1‐methyl substituted tetrazoles. The 1‐methyl‐tetrazoles showed molecular ion peaks while the 2‐methyltetrazoles exhibited an unprecedented [M + 1] peak with no molecular ion.
Field ionization mass spectrometry—I. Nucleosides
Authors: Brown Peter , Pettit George R. , Robins Roland K. 
Published: May 2005

AbstractThe field ionization mass spectra of a series of nucleosides are reported, and compared with spectra obtained by conventional electron‐impact ionization. The latter are complex, with structurally significant molecular ion and sugar cleavage peaks often of low intensity or completely absent. In contrast, the field ion spectra are extremely simple, with all except guanosine (highest mass peak [M — 18]) showing intense molecular ion peaks, and the characteristic sugar (S) and base (B + H) cleavage products as the only other important fragments.
Massenspektrometrie instabiler moleküle—III: Nachweis und untersuchungen zur stabilität chlorsubstituierter dehydrobenzole in der gasphase
Authors: Grützmacher Hans‐Friedrich , Hübner Jürgen 
Published: May 2005

Abstract3,4‐, 3,5‐, 3,6‐, und 4,5‐Dichlordehydrobezol sowie 3,4,5,6‐Tetrachlordehydrobenzol wurden durch Hochvakuumpyrolyse aus den entsprechend substituierten 1,2‐Dijodbenzolen bzw. Phthalsäureanhydriden erzeugt und massenspektrometrisch nachgewiesen. Die Ionisationspotentiale wurden nach dem RPD‐Verfahren gemessen und die Bildungsenthal pien der substituierten Dehydrobenzole abgeschätzt.
De l'origine du pic [M — 1] dans le spectre de masse de la N,N‐diméthylbenzamide
Authors: Biellmann J. F. , Hirth C. G. 
Published: May 2005

AbstractLe pic à [M — 1] dans le spectre de masse de al N,N‐diméthybenzamide provient de la prete d'un hydrogène du noyau aromatique et nonpas d'un des groupes méthyles. La preuve en est faite en comparant les spectres de al N‐trideutériométhyl N‐méthyl‐, N,N‐di(trideutério)méthyl‐ et N,N‐diméthyl 2,4,6‐trideutério bezamide. On décrit la préparation de ces produits.
Charge localization in molecule‐ions upon electron‐impact. Mass spectra of some substituted 1‐carbamoyl‐ and 1‐thiocarbamoyl‐2‐pyrazolines and related compounds
Authors: Tam S. W. 
Published: May 2005

AbstractThe mass spectra of some substituted 2‐pyrazolines and a pyrazolidine are discussed. With the exception of III which favours McLafferty rearrangements prior to fragmentation, I, IV and V fragment to give isocyanate or isothiocyanate radicals and ions with structures corresponding to their heterocyclic molecular compounds. These results which can be explained in the light of the concept of charge localization at preferential sites, are in good agreement with the ionization potential studies on substituted ureas and thioureas.5 Other compounds show simple straight‐forward fragmentations upon electron‐impact.