bluuebunny/crossref_metadata_2025_split huggingface dataset:
1H, 13C and 7Li nuclear magnetic resonance study of the lithium chloride–N,N‐dimethylacetamide system
Authors: Germain J. Saint , Vincendon M. 
Published: May 2005

AbstractThe complex solvent obtained by dissolving 5‐10% of lithium chloride in N,N‐dimethylacetamide (DMA) presents a good method for dissolving highly insoluble polymers, such as cellulose. 1H, 13C and 7Li NMR spectroscopy have been used, together with viscosity and conductivity measurements, for the study of this complex solvent. The 1H and 13C chemical shift variations of DMA, on increasing the lithium chloride concentration, are found to be in opposite directions. The T1 relaxation times show a large decrease in the mobility of DMA in the presence of lithium chloride. Methyl‐β‐D‐glucopyranoside has been used as a model for cellulose in order to investigate the mechanism of solution of this polymer. It was found that each hydroxy group of the solute interacts with one lithium chloride molecule in solution.
1H and 13C NMR studies on 1,3,2‐dioxarsolanes
Authors: Aksnes D. W. , Lie A. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of a series of 1,3,2‐dioxarsolanes have been obtained at 2.1 T and some at 9.4 T. The chemical shifts and spin‐spin coupling constants have been obtained from complete spectral analyses of the 1H and proton‐coupled 13C spectra. The spectral data are interpreted on the basis of two rapidly interconverting half‐chair conformers with a pseudoaxial substituent at arsenic. Unique assignment of syn/anti or cis/trans geometries have been made from 1H or 13C NMR spectroscopy alone. The syn and trans isomers of the 4‐methyl‐ and 4,5‐dimethyl‐1,3,2‐dioxarsolanes, respectively, appear to be conformationally biased towards the forms with pseudoequatorial methyl groups. The general trends in the geminal and vicinal 1H1H and 13C1H coupling constants are interpreted in terms of stereospecific, electronegativity and lone‐pair effects of the oxygen heteroatoms and conformational factors. The NMR data on the 1,3,2‐dioxarsolanes are discussed with reference to related 1,3‐dithoxa‐ and 1,3‐dithia‐ five‐membered rings with As, P, S or C at the 2‐position.
13C and 1H chemical shifts in 2‐benzylidene[3]ferrocenophane‐1,3‐diones. Elucidation of the substituent dependence of carbonyl chemical shifts in different carbonyl derivatives
Authors: Solčániovà E. , Toma Š. , Sališová M. , Liptaj T. 
Published: May 2005

AbstractThe 13C and 1H chemical shifts of the ferrocene moiety, as well as the carbonyl carbons and styrene moiety, of substituted 2‐benzylidene[3]ferrocenophane‐1,3‐diones have been assigned. Correlations of 13C substituent chemical shifts of both carbonyl carbons with the Hammett constants have been found, and the effect of the transmission of substituent effects on these chemical shifts through the styrene moiety is discussed. An explanation is given for the different sensitivities of the carbonyl carbon chemical shifts to the electronic effect of substituents in mono‐ and dicarbonyl derivatives.
Carbon‐13 NMR spectra of some o‐carbonyl benzeneselenenyl derivatives
Authors: Llabrès Gabriel , Baiwir Marcel , Christiaens Lèon , Piette Jean‐Louis 
Published: May 2005

AbstractThe 13C NMR signals have been assigned for some ortho‐carbonyl benzene‐selenenyl derivatives, COR.C6H4. Sex, where R = H, CH3, OCH3 and OC2H5 and X = Cl, Br, CN, SCN, SeCN and CH3. The effects of the nature of R and X have been discussed.
Rotational equilibria in 1,2,6‐trisubstituted pyridinium cations and reactions of 2‐Isopropylpyrylium cations
Authors: Katritzky Alan R. , Vassilatos Socrates N. , Alajarin‐Ceron Mateo 
Published: May 2005

Abstract2‐Isopropyl‐6‐phenyl‐ and 2,6‐diisopropyl‐pyridiniums with bulky 1‐substituents show temperature‐variable NMR spectra which are interpreted in terms of restricted rotation. 2‐Isopropyl‐4,6‐diphenylpyrylium can be deprotonated at the isopropyl group to give an anhydro base which forms new pyryliums with electrophiles.
Spectroscopic elucidation of pseudo‐base formation from benzo[8,9]quinoliziono[4,5,6,7‐fed]phenanthrindyliums
Authors: Katritzky Alan R. , Agha Bushra , de Ville George Z. , Lunt Edward , Podmore Michael L. 
Published: May 2005

Abstract13C and 1H NMR spectra and UV spectra are recorded and assigned for a variety of substituted and hetero derivatives of benzo[8,9]quinolizino[4,5,6,7‐fed]phenanthrindyliums. Large specific effects of traces of water on these spectra are traced to pseudo‐base formation.
Investigations on N,N‐dialkylbenzamides by NMR spectroscopy: 5—Analysis of static and dynamic proton NMR spectra of 2‐fluoro‐ and 2,6‐difluoro‐N,N‐dimethyl‐ and N,N‐diethyl‐benzamides
Authors: Dürst Thomas , Gryff‐Keller Adam , Terpiński Jacek 
Published: May 2005

AbstractThe analysis of static and dynamic proton NMR spectra of 2‐fluoro‐ and 2,6‐difluoro‐N,N‐dimethyl‐ and N,N‐diethyl‐benzamides at various temperatures has been carried out. The conformations of the compounds have been deduced on the basis of long‐range through‐space proton‐fluorine couplings. Free energies of activation of amide rotation have been determined for all compounds, and of carbonyl‐ring rotation for one compound.
The 13C NMR characterization of some 1,2,3,4‐tetrahydro‐1,4‐ethanonaphthalenes
Authors: Smith William B. 
Published: May 2005

AbstractThe 2‐hydroxy and 2‐hydroxy‐3‐methyl isomers of 5,8‐dimethoxy‐1,2,3,4‐tetrahydro‐1,4‐ethanonapthalene have been characterized by 13C NMR with the aid of lanthanide shift reagents. A definite interaction with a syn oxygen, presumably with the lone electron pairs, and the aromatic carbon 8a has been established. This n‐π γ‐effect is not found with a corresponding methyl group. Examples from the literature also evidence the reality of the γ‐effect, which provides a useful structure assignment tool.
Compounds with bridgehead nitrogen: 46—The 1H NMR spectra and stereochemistry of derivatives of 1,3,3a,4,5,6,6a,11a‐octahydroindolo[3,2,1‐ij][3, 1]benzoxazine
Authors: Crabb Trevor A. , Rouse Janet 
Published: May 2005

AbstractThe 1H NMR parameters of the NCH2O protons of the reduced pyrrolo[1,2‐c][1,3]oxazine moiety in rel‐(3aS,6aS,11aS)‐1,3,3a,4,5,6,6a,11a‐octahydro‐6a‐methylindolo[3,2,ij][3, 1]benzoxazine and in the alkaloid rosibiline indicate a trans ring fusion for the grouping. The O‐inside cis‐fused moiety is present in the related rel‐(3aR,6aS,11aS)‐octahydro‐6a‐methylindolo[3,2,1‐ij][3, 1]benzoxazine and in Wieland–Gumlich glycol formal.
Reinvestigation of the structure of 1:3,2:4,5:6‐tri‐O‐isopropylidene‐D‐glucitol by 1H NMR spectroscopy at 250 MHz
Authors: Sohár P. , Kuszmann J. 
Published: May 2005

AbstractThe structure of 1:3,2:4,5:6‐tri‐O‐isopropylidene‐D‐glucitol, which was proposed earlier to be the 1:2,3:5,4:6‐analogue, was re‐detormined by 1H NMR measurement at 250 MHz. The assignments were proved by double resonance experiments. Using the spectral parameters as starting values, the theoretical spectrum of the eight skeletal protons was constructed and the chemical shifts and proton‐proton coupling constants were calculated by iteration (RMS: 0.014) using the PANIC program of Bruker AG.
Double inversion of the secondary nitrogens in cis‐Diaziridinocyclopentane
Authors: Majchrzak Michał W. , Kotełko Antoni , Lambert Joseph B. 
Published: May 2005

Abstract1α,2α,4α,6α,‐3,7‐Diazatricyclo[4.1.0.02,4]heptane (cis‐diaziridinocyclopentane) (1) has been prepared from the analogous cis‐diepoxycyclopentane. Ring opening of the diepoxide with sodium azide produced a pair of regioisomeric azido alcohols. Tosylation and treatment with lithium aluminum hydride produced 1. The dibenzoyl derivative possessed the di‐exo stereochemistry for the tertiary aziridine nitrogens. The 1H spectrum of 1 was temperature dependent. Both the CH and NH resonances underwent decoalescence as the temperature was lowered. Because the rate was independent of concentration, the mechanism is probably inversion of the secondary nitrogen, the first such example to occur by the interchange of two diastereotopic, secondary (NH) amine nitrogens within the same molecule. The free energy of activation at coalescence (0 °C) was measured to be 12.8 kcal mol−1. The unsymmetrical slow exchange of 1 is clearly consistent with the exo,endo stereochemistry for the secondary aziridine nitrogens, possibly stabilized by intramolecular attraction.
Acquisition times, relaxation rates and solvent and temperature effects as sensitivity parameters for quadrupolar nuclei
Authors: Gerothanassis Ioannis P. 
Published: May 2005

AbstractThe relationship between the signal‐to‐noise ration and T2 and, hence, the line width of a resonance for quadrupolar nuclei, with particular reference to 17O at natural abundance, is discussed. Emphasis is placed on the importance of choosing appropriate FID acquisition times related to the T2 values or resonance widths of the quadrupolar nuclei. When this is feasible (i.e. when the principal resonances in a spectrum have similar widths) the signal‐to‐noise ratio attainable against a flat base line in a given time of spectral accumulation is independent of resonance line width. Although resolution improvements can be made by using appropriate solvents or elevated sample temperatures, the sensitivity has been to be strongly dependent on the acquisition parameters used.
Barriers to internal rotation in neopentylbenzenes substituted on the benzyl group. A 13C NMR band shape study
Authors: Andersson Sven , Drakenberg Torbjörn 
Published: May 2005

AbstractTwo series of neopentylbenzenes with one or two substituents on the benzyl group have been synthesized. In one series the substituents were H, F, Cl, Br, I, OCH3, OCOCH3, OSi(CH3)3 CH3 and CH2CH3, and in the other OH and R [R  H, CH3, CH2CH3, (CH2)3CH3, CH(CH3)2 and C(CH3)3]. Barriers to internal CC and CC rotation have been estimated by 13C NMR band shape methods. Estimated barriers were found to increase as the size of the substituent increases. The results are discussed in terms of possible initial and transition states, based on summations of results from molecular mechanics (MM) calculations, using the Allinger MMP1 program. Barriers estimated experimentally are compared with results from other systems found in the literature.
Electron impact and molecular dissociation. Part XIX. Mass spectral studies of some binuclear metal complexes
Authors: Preston F. J. , Reed R. I. 
Published: May 2005

AbstractThe spectra of certain deuteriated binuclear chromium complexes have been obtained which help to elucidate some of the fragmentation processes of the molecular ion.The effect of the relative strengths of the metal‐ligand and metal nitrosyl bonds is also discussed.
Massenspektren Schwach Angeregter Moleküle. 4.Mitteilung
Authors: Remberg G. , Remberg E. , Spiteller‐Friedmann M. , Spiteller G. 
Published: May 2005

AbstractDie thermische Anregungsenergie der Moleküle beeinflußt mehrstufige Abbaureaktionen aliphatischer Verbindungen im massenspektrometer sehr stark. Thermische Anregung erhalten die Moleküle vielfach erst durch Wandstöße in der Ionenquelle. Da in den Wenigsten Fällen die Ionenquellentemperature völlig konstant gehalten werden kann, unterscheiden sich Spektren ein und derselben Verbindung oft in ihren Intensitätwerten voneinander. Diesem Umstand sollte bei der Anlage von Spektrensammlungen Rechnung getragen werden.Durch Erniedrigung von Elektronenenergie und Ionenquellentemperatur lassen sich mehrstufige Abbaureaktionen os lenken, daß vorzugsweise nur primäre Spaltprodukte entstehen. Die Spektren werden dadurch qualitativ besser auswertbar. Bie Anwendung dieses Verfahrens auf bifunktionelle aliphatische Verbindungen Können nahezu sämtliche Spaltstücke ovn Molekülionenspezies abgeleitet werden, die an der einen oder anderen funktionellen Gruppe ionisiert wurden. Je nach der Mange der durch Ionisation an einer der Gruppen entstandenen Fragmente kann man daher den Einfluß der Substituenten miteinander vergleichen und diese nach steigender Einflußnahme auf die Bruchstückbildung in einer Reihen anordnen. Es ergibt sich danach etwa die folgende Reihung:
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The mass spectra of some guanidines
Authors: Beynon J. H. , Hopkinson J. A. , Williams A. E. 
Published: May 2005

AbstractThe mass spectra of guanidine and ten of its derivatives have been studied under both high and low resolution conditions. Evidence was detected for the migration of methyl groups, the formation of intermediate three‐membered ring structures and decompositions involving expulsion of N. with release of kinetic energy.
Organic mass spectrometry—X. Electron impact fragmentations of alkylthio group in 2‐alkylthio‐5‐aminothiazolo[5,4‐d] pyrimidines
Authors: Tatematsu A. , Sugiura S. , Inoue S. , Goto T. 
Published: May 2005

AbstractIn order to discuss hydrogen transfer in the skeletal fragmentation of thioethers on electron impact, mass spectra of a series of 2‐n‐alkylthio‐5‐aminothiazolo [5,4‐d]pyrimidines have been determined. To aid the interpretation of the hydrogen migration, deuterium‐labeled compounds which are substituted with deuterium in each position of 2‐n‐butylthio‐5‐aminothiazolo‐pyrimidines were studied. By correlation of the spectra obtained from such labeled compounds, the initial hydrogen migration in the fragmentation to produce [M  SH], [MS  CH3] and m/e 184 ions is concluded to be as follows: migration of the α‐hydrogen atom to the sulfur induces formation of the [M  SH] ion; migration of the β‐hydrogen atom to the sulfur or nitrogen atom by a McLafferty rearrangement induces formation of the m/e 184 ion; and migration of γ‐hydrogen atom to the sulfur induces formation of the [M  SCH3] ion.
Massenspektrometrische Fragmentieungen Aomatischer Isocyanide
Authors: Zeeh Bernd 
Published: May 2005

AbstractDie Massenspekren von 19 aromatischen Isocyaniden werden angegeben. Hauptmerkmal des Elektronenstoß‐induzierten Zerfalls dieser Verbindungen ist der Verlust von HCN, der gewöhnlich von einem metastabilen Peak begleitet wird. Obsleich dieser Prozeß charakteristisch ist für das Verhalten von aromatischen Isocyaniden, tritt er mehr und mehr in den Hintergrrund, wenn andere leicht spaltbare Bindungen im Molekül vorhanden sind. 2,4,6‐d3‐Phenylisocyanid (Ib) spaltet aus dem Molekülion vorwiegend DCN ab, während 2,4,d2‐1‐Naphthyl‐isocyanid (IIb) hingegen HCN eliminiert. Es wird deshalb angenommen, daß bei der Abspaltung von HCN aus aromatischen Isocyaniden der dazu benötigte Wasserstoff aus einer spezifischen Stellung des Benzolkerns kommt und keine statistische Verteilung der Wassertoff‐Atome vor der Fragmentierung eintritt.
Organic ions in the gas phase—XXI. Competitive primary loss of C2H4 and CO from 1‐tetralone under electron impact
Authors: Meyerson Seymour , Vander Haar R. W. 
Published: May 2005

AbstractCompeting primary reactions by which 1‐tetralone loses C2H4 and CO give rise to a doublet at mass 118 in the high‐resolution mass spectrum corresponding to 96·4% C8H6O+ and 3·6% C9H10+, respectively. Study of the remainder of the spectrum however, suggests that these intensities constitute a poor measure of the relative importance of the two reaction paths. The C9H10+ ion evidently degrades more readily than C8H6O+, since an estimated 26% of the ions arising in these paths involve primary loss of CO. This estimate is supported by voltage dependence of the intensity distribution between the members of the doublet. As ionizing voltage is decreased, the intensity distribution is constant to about 20 volts, but between 20 and 10 volts the value for C9H10+ rises smoothly from about 3.5% to about 25%.
The mass spectra of some cyclic ethers
Authors: Smakman R. , De Boer Th. J. 
Published: May 2005

AbstractThe mass spectral fragmentations of the saturated five‐, six‐ and seven‐membered ring ethers have been determined by studying their site‐specifically deuterated analogues by both high and low‐resolution mass spectrometry.The initial processes, governing the fragmentations of the cyclic ethers are shown to be identical with the well‐known processes of linear nonbranched ethers, i.e. predominant α‐fisson in the lower members and predominant carbon‐oxygen fisson with charge retention on the carbon atom in the higher members.
Electron‐impact studies of organometallic molecules—VI. Some transition metal derivatives of alicyclic fluorocarbons
Authors: Bruce M. I. 
Published: May 2005

AbstractThe mass spectra of a series of alicyclic fluorocarbon complexes of manganese, rhenium, iron and ruthenium are described and discussed. It is shown that the breakdown of these complexes after ionization depends on the nature of the metal, and of the other groups attached to the metal. Effects due to elimination of metal halides, formation of metal fluoride ions, and ligand transfer reactions are found, and result in significant differences in the fragmentation patterns of the complexes from those of the parent fluorocarbons.
The mass spectrometry of volatile derivatives—II: N‐alkyl trifluoracetamides
Authors: Saxby M. J. 
Published: May 2005

AbstractUnder electron‐impact, N‐alkyl trifluoracetamides exhibit peaks due to [CF3]+ and [M  CF3]+. Ions corresponding to [COCF3]+ are absent. The base peak in many straight chain derivatives occurs at m/e 126 due to alkyl radical loss from the molecular ion; the mass of this ion rising to m/e 140 in the α‐substituted N‐sec‐butyltrifluoracetamide and to m/e 154 in the tert‐butyl derivative. High resolution measurements on a number of peaks indicate that they originate by loss of HF from other fragment ions.
An investigation of tautomeric equilibria by means of mass spectrometry
Authors: Zamir Lolita , Jensen Bror Skytte , Larsen Elfinn 
Published: May 2005

AbstractChanges in the mass spectra with inlet temperature were used in this work to demonstrate the dependence of keto‐enol tautomerism of acetylacetone, 3‐methyl acetylacetone and 3‐allyl acetylacetone on temperature.The largest dependence of temperature were shown by the ion [M  42]+. arising from a McLafferty type rearrangement and by the ion [M  Me]+ resulting from simple α‐cleavage. The ion [M  42]+. peak increases with the temperature of the inlet system while the ion [M  Me]+ peak decreases. By assuming that the ion [M  42]+. represents the keto form and that the ion [M  Me]+ represents the cis‐enol form (stabilized by the hydrogen bond) one sees that the direction of the intensity variation of these peaks with temperature is in accord with the expected change of keto‐enol tautomerism with temperature. A quantitative correlation on the basis of the above assumptions is also approached.Recording of the mass spectra of these three β‐diketones at different energies of the incident electrons enables us to estimate whether or not the particular ions present in the mass spectra result from energetically favourable processes.The variation of the intensities of the peaks with the temperature of the inlet at different electron energies is also discussed.
The formation of the styryl ion in the mass spectra of cinnamyl compounds
Authors: Brittain E. F. H. , Kelly J. P. , Mead W. L. 
Published: May 2005

AbstractThe formation of the styryl ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm PhCH = }\mathop {\rm C}\limits^{\rm + } {\rm H} $\end{document} in the mass spectra of some cinnamic compounds is shown to occur via the intermediate formation of the cinnamoyl ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Ph} - {\rm CH} = {\rm CH} - {\rm C} \equiv \mathop {\rm O}\limits^{\rm + } $\end{document} rather than by direct cleavage of the bond α to the double bond.
The structural significance of doubly charged ion spectra. Phenylenediamine derivatives
Authors: Vouros P. , Biemann K. 
Published: May 2005

AbstractThe distribution of doubly charged ions found in the mass spectra of various N, N′‐alkyl substituted phenylenediamines is compared to that of their singly charged counterparts. Structural and electronic requirements for the resonance stabilization of doubly charged organic ions are suggested and it is shown that doubly charged ions could be used to differentiate between certain structural isomers which give practically identical singly charged ions. The doubly charged ions were distinguished from singly charged ions of the same integral m/e value by high resolution techniques.
Mass spectrometry of five classes of trityl compounds‐loss of 12C from (C6H5)313CH
Authors: Berlin K. Darrell , Shupe R. D. 
Published: May 2005

AbstractThe mass spectra of 25 triphenylmethyl (trityl) substituted compounds have been recorded. The trityl cation m/e 243 appears as a peak of major intensity for all classes of compounds examined; these contained trityl‐carbon, trityl‐nitrogen, trityl‐oxygen or trityl‐sulfur bonds. Fragmentation of the non‐trityl portion of the molecules produced simple ions whose origin was predictable or of low intensity. A mechanism for the decay of the trityl cation is presented which is based upon retention of the α‐carbon. Supporting evidence was afforded by mass spectral analysis of (C6H5)313CH in which all fragments from the trityl cation appear to retain nearly all of the 13C.
Mass spectra of substituted uracils
Authors: Reiser R. W. 
Published: May 2005

AbstractThe mechanisms for the major fragmentations obtained with selected substituted uracils are discussed. Interpretation of data was facilitated by use of metastable peaks, high‐resolution data, and low‐voltage spectra.The major fragmentation obtained with N‐alkyl substituted uracils, when the alkyl group contains 2 or more carbons, is due to cleavage of the alkyl substituent. This cleavage is accompanied by a rearrangement of 1 or 2 hydrogens from the alkyl group to the uracil ring. Possible mechanisms for the rearrangements are discussed. It was found that the molecular ion of 1‐ and 3‐alkyl substituted uracils (where the alkyl group has 2 or more carbons) does not undergo the expected ‘retro Diels‐Alder Reaction’. Instead, the odd‐electron ion formed by loss of the alkyl substituent with a single hydrogen rearrangement undergoes this reaction (loses HNCO). Since it is formed as a secondary reaction product, the relative abundance of the ‘retro Diels‐Alder’ fragment is low compared to what is obtained in the spectra of the simple uracils.The ‘retro Diels‐Alder Reaction’ can be used to differentiate between 2‐ and 4‐thiouracils, and between 1‐ and 3‐methyl and phenyl substituted uracils. It was found that 1‐ and 3‐alkyl substituted uracils (alkyl group of 2 or more carbons) can be differentiated by the mass of the M‐alkyl fragment since the 3‐substituted compounds give predominantly a double hydrogen rearrangement and the 1‐substituted compound gives mainly a single hydrogen rearrangement. In addition the intensity of the molecular ion, relative to the M‐alkyl ion, is considerably stronger in the 1‐substituted uracils.
Fragmentation of some even‐electron nitroaromatic ions: The question of the nitrotropylium ion
Authors: Shapiro Robert H. , Serum James W. 
Published: May 2005

AbstractThe behavior of the even‐electron mass 150 ions, (presumably nitrobenzoyl cations) generated by simple α‐cleavage of m‐ and p‐nitrobenzoic acid derivatives, undergo two competing secondary fragmentations to yield odd‐electron ions by the expulsion of NO and NO2. Expulsion of NO from the mass 150 ions from p‐nitro compounds is far greater than expulsion of NO from those generated from m‐nitro compounds. In addition, the behavior of the even‐electron mass 136 ions, generated from m‐ and p‐nitrobenzyl compounds, was compared to that of the mass 150 ions and they were found to decompose in a similar fashion. From our results we conclude that the decomposing mass 136 ions produced from either the m‐ or p‐nitrobenzyl compounds, or both, do not have the nitropylium structure; our data are more consistent with the decomposing ions having nitrobenzyl structures.