bluuebunny/crossref_metadata_2025_split huggingface dataset:
13C NMR shifts and conformations of substituted indans
Authors: Agrawal Pawan Kumar , Schneider Hans‐Jörg , Malik Mangel S. , Rastogi Shri Nivas 
Published: May 2005

Abstract13C NMR spectra of indan derivatives bearing substituents in the 1, 2, 5 and 6 positions are reported and assigned by LIS measurements and other techniques. Epimeric indanes bearing vicinal oxygen and phenyl or benzyl substituents show ring carbon shielding in the cis relative to the trans isomers, which is compared with corresponding cyclopentane shifts, and indicates the predominance of envelope conformations with pseudoaxial oxygen substituents for the cis isomers. Acetylation shifts show consistently larger shielding at C‐β for the trans compounds. Introduction of oxygen at C‐5 leads to asymmetric shielding effects at the ortho carbon atoms as soon as there is a substituent in the para position which can participate in mesomeric forms.
Rotational isomerism about the C‐αC‐β bonds in sulphur‐containing amino acids and their non‐sulphur‐containing isoesters
Authors: Picur B. , Siemion I. Z. 
Published: May 2005

AbstractThe conformation of the methionine side‐chain in methanolic solution does not differ from that of norleucine; some differences, however, were observed for S‐methylcysteine and norvaline derivatives. It was also shown that the temperature coefficients of the CH2 group resonances could be used for the assignment of the HR‐β and HS‐β signals.
Dynamic stereochemistry of imines and derivatives: 15—Carbon‐13 NMR studies of aryl‐substituted imines and oxaziridines
Authors: Jennings W. Brian , Wilson Valerie E. , Boyd Derek R. , Coulter Peter B. 
Published: May 2005

Abstract13C chemical shifts for several series of cis‐ and trans‐N‐alkylimines and oxaziridines bearing para‐substituted C‐phenyl rings are reported and correlated with dual substituent parameters. The 13CN and oxaziridine ring carbon shifts correlate primarily with the inductive/field parameters, σ1, whereas both resonance and inductive terms generally contribute about equally to the long‐range substituent effects on alkyl side‐chain chemical shifts. Correlations on diastereoisomeric imines show that the transmission of substituent effects can be significantly affected by the E–Z configuration. Aromatic carbon chemical shifts in imines are discussed in relation to the E–Z configuration and the conformation around the aryl—imino bond.
13C1H coupling constants in 9, 10‐dihydroanthracene
Authors: Holak T. A. , Aksnes D. W. , Syguła A. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of 9,10‐dihydroanthracene have been obtained at 2.1 and 9.4 T using selective decoupling of the methylene protons. Complete spectral analyses of the experimental spectra have provided the chemical shifts and coupling constants. The 13C1H coupling constants in 9, 10‐dihydroanthracene and biphenylene have been well accounted for by MNDO theoretical calculations of the molecular geometries and bond orders in these compounds.
Some calculations of the solvent dependences of phosphorus nuclear shielding
Authors: Nalamphun B. , Webb G. A. 
Published: May 2005

AbstractSome CNDO/S parameterized calculations of phosphorus shielding, as a function of the dielectric constant of the medium, are presented. Pople's SOS perturbation approach together with the solvaton model are employed. For trivalent phosphorus compounds a shielding decrease by up to 15 ppm is predicted as ε increases from 1 to 80. For pentavalent phosphorus a much smaller shielding variation, in the opposite direction, is predicted. In general, a consideration of changes in phosphorus charge density is insufficient to account for the variation in nuclear shielding.
Oxygen‐17 nuclear magnetic resonance study of some oxirane derivatives
Authors: Sauleau A. , Sauleau J. , Monti J. P. , Faure R. 
Published: May 2005

AbstractThe 17O chemical shifts of seventeen variously substituted oxiranes have been measured in CDCI3 solution. Deviations of δo from additivity have been interpreted in terms of steric effects and loss of conjugation. Moreover, in the case of certain cis‐ and trans‐dimethyl‐substituted compounds, 17O NMR allows a differentiation between the different molecular configurations.
Some INDO/SSOS calculations of the effects of hydrogen bonding on the nitrogen shielding of some heterocycles
Authors: Lamphun B. Na , Webb G. A. , Witanowski M. 
Published: May 2005

AbstractSome INDO/S parameterized SOS shielding calculations are reported for the nitrogen nuclei of some N‐heterocycles. Hydrogen bonding with H2O and CF3CH2OH is incorporated in a supermolecule approach. The calculated effects of hydrogen bonding are found to be in satisfactory agreement with observed nitrogen shielding variations upon a change of solvent.
Carbon‐13 NMR spectra of Δ4(20).11‐ taxadiene derivatives
Authors: De Marcano Deanna , Méndez Bernardo , De Méndez Jeannette , Monasterios José , Rojas Aníbal C. , Halsall Thomas G. 
Published: May 2005

AbstractThe 13C NMR spectra of a series of some Δ4(20),11‐taxadiene derivatives are reported. A detailed analysis of their assignments is presented.
29Si chemical shifts and additivity in pertrimethylsilylated O‐methyl, O‐benzyl, O‐benzoyl and O‐acetyl methyl β‐D‐xylopyranosides
Authors: Schraml J. , Petráková E. , Pihar O. , Hirsch J. , Chvalovský V. 
Published: May 2005

Abstract29Si chemical shifts in pertrimethylsilylated O‐methyl, O‐benzoyl, O‐benzoyl and O‐acetyl methyl β‐D‐xylopyranoside derivatives are reported. The chemical shifts in monotrimethylsilyl derivatives with the same O‐substituents are in the order: δ(Si‐2) > δ(Si‐4) > δ(Si‐3). When the chemical shifts in bis (trimethylsilyl) and tris(trimethylsilyl) derivatives are assigned according to this rule, all the chemical shifts agree well with a direct additivity rule. The only significant deviation from additivity occurs for methyl 2,4‐di‐O‐benzoyl‐3‐O‐trimethylsilyl‐β‐D‐xylopyranoside, which has a different average conformation from the other compounds studied.
Dynamic1H NMR spectroscopy of η2‐ethylene transition metal complexes
Authors: Benn Reinhard 
Published: May 2005

AbstractThe low‐temperature1H NMR spectra of bis(ethylene)trimethylphosphinenickel (1), η5‐cyclopentadienyl(ethylene)methylnickel (2a), bis(ethylene)‐η5‐cyclopentadienylcobalt (2b), [bis(1‐ethyl‐2,4,6‐triphenylphosphorinyl)nickel]P,P′‐nickel(ethylene) (3) and η5‐cyclopentadienyl(ethylene)hydrido(triphenylphosphine)ruthenium (4) exhibit {AA′B′B} (1) {ABB′A} (2a and 2b), {ABA′B′} (3) or {ABCD} (4) spin patterns, respectively, for the complexed ethylene. A full line shape analysis including all the proton couplings was performed for the ethylene rotation in 1, 2a and 2b. In addition to olefin rotation, a reversible intramolecular β‐H‐elimination was confirmed for 4 by magnetization transfer experiments.
Mass spectral correlations for some fluorinated alkanes
Authors: McCarthy E. R. 
Published: May 2005

AbstractThe cracking patterns of thirty‐three fluorinated methanes, ethanes and propanes have been tabulated. For many of the compounds molecular ions were not observed. A comparison has been made of some of the halomethyl ion abundances with stabilization energies that have recently been derived from appearance potential measurements. Rearranged halomethyl ions occur frequently in the fluoroethane spectra. Their intensities often exceed those resulting from simple carbon bond rupture.
The mass spectra of metal complexes of dibenzoylmethane
Authors: Lacey M. J. , Macdonald C. G. , Shannon J. S. 
Published: May 2005

AbstractThe mass spectra of a series of metal complexes of dibenzoylmethane have been rationalized. The paths of novel rearrangement reactions involving both hydrogen and oxygen migration may differ according to the type of metal atom in the complex. Further examples are proposed of the effect of metal valency changes in ion reactions.
The mass spectrum of 1‐(2‐thienyl) hexane‐1‐13C
Authors: Foster Norman G. , Higgins Robert W. 
Published: May 2005

AbstractThe mass spectrum of 1‐(2‐thienyl) hexane‐1‐13C is reported. The principal fragmentation routes ofthe parent ion are delineated. Beta cleavage of the alkyl chain predominates, and the label retention indicates that the alpha carbon atom remains with the charged ring moiety. A substantial part of the m/e 97 ion undergoes a ring expansion to a six membered ring. A small amount of alpha cleavage of the alkyl chain occurs with the expected loss of the label. Further fragmentation of the ions from initial alpha or beta cleavage produces similar fragment ions. It is noted that many of the neutral particles lost in the formation of the fragment ions are typical of those encountered in the alkylbenzenes or other aromatic ion systems.
Organic ions in the gas phase. Part XX. Mass spectra of phenylthiophenes
Authors: Meyerson Seymour , Fields E. K. 
Published: May 2005

AbstractThe mass spectra of 2‐ and 3‐phenylthiophenes and their phenyl‐d5 counterparts reveal that the thienyl ring is markedly more reactive than the phenyl ring under electron impact. In one process, that leading to loss of C2H2S, the atoms lost are apparently derived solely from the thienyl ring, quite probably from the original molecular configuration.
High resolution mass spectrometry—I. Some substituted δ‐lactones
Authors: Millard B. J. 
Published: May 2005

AbstractThe mass spectra of some δ‐lactones substituted in various positions by methyl groups have been studied both by accurate mass measurements at high resulution and by deuterium labelling. The loss of carbon dioxide has been shown to be important only for a mono‐substituted lactone. A fragmentation mode common to all the lactones studied is the elimination of the ring oxygen atom, plus the adjacent carbon atom with its substituents, as a neutral carbonyl molecule such as formaldehyde, acetaldehyde or acetone. Deuterium labelling has uncovered the existence of a rearrangement involving hydrogen transfer in an even‐electron ion, and a mechanism involving a six‐membered transition state is proposed for this. The bond fissions, common to all the lactones, by which the principal ions in the mass spectra arise, are summarised.
High resolution mass spectrometry.—II Some substituted benzothiazoles
Authors: Millard B. J. , Temple A. F. 
Published: May 2005

AbstractThe mass spectra of nineteen substituted benzothiazoles have been recorded and the identity of the various ions in the mass spectra has been established by high resulution (accurate) mass measurement. Deuterium labelling has been used to elucidate the fragmentation processes of these compounds. The parent compound of the series, benzothiazole, exhibits the loss of hydrogen cyanide and carbon monosulphide from the parent ion as the most important decomposition pathways. The hydrogen atom concerned in the loss of hydrogen cyanide is shown to originate from the 2‐position of benzothiazole, while in 2‐substituted benzothiazoles, different mechanisms are apparent for the loss of hydrogen cyanide, and these are clarified by deuterium labelling. Some substituted benzothiazoles can lose sulphur from their molecular ions, a process which does not occur in benzothiazole itself. The substituted benzothiazoles undergo many other types of fragmentations, in some cases retaining the substituent, and in other cases losing it prior to collapse of the thiazole ring.
The mass spectra of some chlorinated pesticidal compounds
Authors: Damico J. N. , Barron R. P. , Ruth J. M. 
Published: May 2005

AbstractThe mass spectra of nine bridged polycyclic chlorinated pesticidal compounds have been investigated, and fragmentation modes to account for the more abundant ions are postulated. The principal features of the spectra are ions corresponding to a set of retro‐Diels‐Alder decompositions, ions resulting from successive losses of Cl, HCl, or both, ions produced by combinations of a retro‐Diels‐Alder process with a preliminary or subsequent loss of Cl or HCl, and ions whose processes of formation more specifically involve the epoxide group.
Mass spectometry of aralkyl compounds with a functional group—VI1: Mass spectra of 1‐phenylethyanol‐1, 2‐phenylethanol‐1 and 1‐phenylpropanol‐2
Authors: Nibbering N. M. M. , De Boer Th. J. 
Published: May 2005

AbstractMass spectra of 1‐phenylethanol‐1 and its analogues, specifically deuterated in the aliphatic chain, suggest that the [MCH3]+ ion is represented partly by an α‐hydroxybenzyl fragment. Moreover, the molecular ion loses successively—after scrambling of all hydrogen atoms, except those of CH3a hydrogen atom and C6H6, generation the CH3CO+ ion.Diffuse peaks, found in the spectra of of 2‐phenylethanol‐1 and its analogues, specifically deuterated in the aliphatic chain and in the phenyl ring, show that the molecular ion loses C2H4O, possibly via a four‐center mechanism, after an exchange of aromatic and hydroxylic hydrogens.Mass spectra of 1‐phenylpropanol‐2 and its analogues, specifically, deuterated in the aliphatic chain, demonstrate that in the molecular ion exclusively the hydroxyl hydrogen atom is transferred to one of the ortho‐positions of the phenyl ring via a McLafferty rearrangement, generating the [M  C2H4O]+ ion. Furtherore, an eight‐membered ring structure is proposed for the [M  CH3]+ ion to explain the loss of H2O and C2H2O from this ion after an extensive scrambling of hydrogen atoms.
Pharmacologically interesting compounds—I: High resolution mass spectra of phenothiazines
Authors: Gilbert J. N. T. , Millard B. J. 
Published: May 2005

AbstractThe mass spectra of twenty‐six commercially available medicinal phenothiazines have been determined at high resolution. In each compound, the side chain attached to the 10‐position of the phenothiazine ring contains nitrogen and fission of the CC bond α to this nitrogen gives in most cases the base peak. Some of the compounds are also substituted at the 2‐position and this substituent generally remains intact, though some substituents such as acetyl, propionyl, methoxyl and methylthio can undergo fragmentation. Fragmentations fall into three groups; those which give ions representing a part of the side chain; those which give ions representing the intact phenothiazine ring with part of the side chain attached; those which give ions representing a partially fragmented ring system.
Electron‐impact fragmentation of aliphatic polynitro compounds
Authors: Larkins J. T. , Saalfeld F. E. , Kaplan Lloyd 
Published: May 2005

AbstractThe mass spectra of two series of aliphatic polynitro compounds are reported and discussed. The fragmentation patterns of aliphatic nitro and polynitro compounds are similar in that no appreciable molecular ion current is observed; however, there are several other features in the fragmentation of aliphatic polynitro compounds which differ from that of nitroalkane spectra. Both series of compounds studied‐C(NO2)x(CH3)4−x, where x = 4 to 0 and C2(NO2)x(CH3)6−x, where x = 6,4,2‐show a decrease in the number and intensity of alkylions with an increase in the NO+ and NO2+ ion current as x increases. The main ions resulting from the more nitrated compounds are [NO]+, [NO2]+, [CO2]+. and [CH3CO]+, whose noncharged counterparts are the principal species produced in the detonation of these compounds. This similarity of the products of the two processes suggests the use of mass spectroscopy for the investigation of the initial explosive processes. The principal fragmentation pathways of the polynitroalkanes have been elucidated by exact mass measurements and the observation of metastable ion transitions.
Mass spectrometry and organic analysis—XIII. The mass spectra of doubly unsaturated carbonyl compounds
Authors: Thomas A. F. , Willhalm B. , Müller Regula 
Published: May 2005

AbstractIn 2,6‐di‐unsaturated carbonyl compounds, two successive, site‐specific hydrogen transfers are necessary to account for the loss of carbon atoms 1, 2, 3 and 4, together with one hydrogen from C‐8. The deuterated methyl geranate required for this study was readily converted to pseudo‐ionone, in which a similar fission was shown to occur. Previous predictions about the β‐ionone mass spectrum2 have been shown to be substantially correct, and its similarity to the mass spectra of benzylidence acetones is pointed out.
Ionisation et fragmentation en spectrometrie de masse—I: Sur la répartition de la charge positive entre fragments provenant de mêmes ruptures
Authors: Audier H. E. 
Published: May 2005

AbstractLors d'une rupture en spectrométrie de masse, la charge positive demeure préférentiellement sur le fragment de potentiel d'ionisation le plus bas. Ce critère, qui fut mis en évidence sur les alcanes, a été généralisé à divers types de fragmentations.
The mass spectra of dunnione and hydrodunnione diacetate
Authors: Buckle D. R. , Waight E. S. 
Published: May 2005

AbstractThe synthesis of dunnione (II) from 2‐hydroxynaphtha‐1,4‐quinone has been improved and used to prepare three deuteriated analogues. The mass spectra of these compounds and of the products of their reductive acetylation and deuterioacetylation have been measured and used to interpret the mass spectrum of atrovenetin.
Die β,γ‐Spaltung von Carbonylver‐Bindungen und derivaten als Allgemeingültige Hauptabbau‐Reaktion IM Massenspektrometer
Authors: Kraft M. , Spiteller G. 
Published: May 2005

AbstractAliphaten mit polarisierten Doppelbindungen (I) zeigen bei Elektronenbeschuß im Massenspektrometer häufig eine vorzugsweise Spaltung einer zur funktionellen Gruppe β,γ‐ständigen CC Bindung. Das dadurch Entstehende heteroatomhalitige Fragment ist mit einer konjugierten Doppelbindung als (IV) zu formulieren. Es entsteht im Zuge einer doppelten Wasserstoffumlagerung (I)→(II)→(III)→(IV). Deuteriummarkierung, Hochauflösung und metastbile Ionen beweisen, daß dieses Ion (IV) durch McLafferty‐Umlagerung weiter abgebaut werden kann.
The mass spectra of 1,1,1,2‐Tetrafluoroethane and 1,1,2,2‐Tetrafluoroethane
Authors: MacKnight S. D. , Teng Lei , Jones W. E. 
Published: May 2005

AbstractMass spectra of the two compounds 1,1,1,2‐Tetrafluoroethane and 1,1,2,2‐Tetrafluoroethane are presented.
Formation of [M — C2H4]+· in O‐d1‐butyric acid
Authors: Fairweather R. B. , McLafferty F. W. 
Published: May 2005

AbstractThe mass spectrum of CH3CH2CH2COOD shows no observable loss of C2H3D. This indicates for this compound that either the McLafferty rearrangement is concerted, or that the second step (olefin loss) is very fast in comparison to the reverse transfer of hydrogen back to the methylene radical.
Evidence for aryl participation in mass spectrometric fragmentation processes
Authors: Richter W. J. , Vetter W. 
Published: May 2005

AbstractWhile heterolysis of oxonium ions generated upon electron‐impact in the mass spectrometer is a well documented phenomenon in the fragmentation of aliphatic ethers, little analogy exists for structurally comparable immonium ions. Exceptions are ions of the latter class in which dissociation is facilitated by the presence of proper substituents in position allowing satabilization of daughter ions. Two main types of subtitution were explored providing(1) resonance stabilization of the product ions by aryl substituents in benzylic,heterolysis,and (2) aryl neighboring group participation in homobenzylic heterolysis, possibly yielding phenonium ions (or isometric ions via further rearrangement) as stable products in the gas phase. In the discussion emphasis will be placed on Case 2.
Massenspektrometrische Untersuchungen an Heterocyclen—III: Thioxanthen, Thioxanthon und Phenothiazin Sowie deren S‐oxide
Authors: Heiss J. , Zeller K.‐P. 
Published: May 2005

AbstractDas massenspektrometrische Fragmentierungsverhalten schwefelhaltiger Dibenzoheterocyclen und deren S‐oxide wird mit Hilfe exakter Massenmessungen untersucht. Die Stabilität der Molekülionen und der Zerfall hängen stark von der Art der Zweiten Atomgruppe im zentralen Sechsring ab. Für die Ketenabspalutung aus den N‐Acetylderivaten von Phenothiazin und dessen S‐Oxiden werden Mechanismen diskutiert.
Cortisol‐eine ausgezeichnete Testsubstanz für die Qualitätsprüfung von Einführsystemen
Authors: Spiteller‐Friedmann Margot , Spiteller Gerhard 
Published: May 2005

AbstractCortisol ist thermisch instabil. Es zersetzt sich leicht unter Verlust von Keten und Wasser, Das Spektrum das entstehenden 11β‐Hydroxy‐Δ4‐androsten‐3,17‐dions überlagert sich dem Cortisolspektrum, das man frei von Zerstezungsprodukt nur unter sorgfältiger Einhaltung der Aufnahmebedingungen erhält Das thermische Zersetzungsprodukt läßt sich leicht an seinem Molekül‐Ion der Masse 302 und einem Schlüsselbruchstück der Masse 163 erkennen, die im Cortisolspektrum nahezu völlig fehlen, so daß Cortisol eine ausgezechnete Testsubstanz zur Qualitätsprüfung vonEinlass‐Systemen darstellt.
Mass spectra of alditol trifluoroacetates
Authors: Chizhov O. S. , Dmitriev B. A. , Zolotarev B. M. , Chernyak A. Ya. , Kochetov N. K. 
Published: May 2005

AbstractThe trifluoroacetyl derivatives of alditols are convenient compounds for mass spectrometric investigation as they are easily obtainable and highly volatile. They show simple fragmentation patterns with intensive peaks in the high mass range. Trifluoroacetates of alditols may be used for detection and location of deoxy groups in the molecule.
Substituent effects on ion abundances and energetics in substituted acetophenones
Authors: Chin Margaret S. , Harrison A. G. 
Published: May 2005

AbstractBased on the quasi‐equilibrium theory of mass spectra it is shown that the intensity ratio [A]+/[M]+, where [A]+is a fragment ion and [M]+is the molecular ion, is given by [A]+/[M]+= f′ (k1/kt) ((1/f) − 1), where f is the fraction of molecular ions with insufficient energy to fragment, f′ is the fraction of [A]+ions with insufficient energy to fragment, and k1/ktis the fraction of fragmenting molecular ions which form [A]+. For substituted acetophenones it is shown that f depends on the substituent present and that f′ k1/ktis also substituent dependent for formation of both [CH3CO]+and [YC6H4CO]+. It is also shown that no direct information concerning the effect of a substituent on the rate of a particular fragmentation reaction can be obtained from intensity studies.The ionization potentials of the parent molecules and the appearance potentials of the [YC6H4CO]+fragment ions have been measured for fifteen substituted acetophenones and the correlations with substituent constants are discussed.
The electron‐impact‐induced fragmentation of n‐alkyl cyanides
Authors: Heerma W. , De Ridder J. J. , Dukstra G. 
Published: May 2005

AbstractThe mass spectra of the alkyl cyanides up to n‐pentyl cyanide were studied. Using metastablel ion transitions, appearance potentials and deuterium labelling, the fragmentation patterns, spectral characteristics and trends for this series can be given. The investigation of labelled compounds demonstrates the specificity of rearrangement and normal decomposition processes. Alkyl ions in nitriles are produced by simple cleavage of the carbon‐carbon bond, while ions of the type [M –alkyl]+, which at the first sight could originate in the same way, are presumably formed via cyclic intermediates and are in fact rearrangement ions.Apart from the known γ and δ‐hydrogen rearrangements, there is novel evidence for a β‐hydrogen rearrangement via a five‐membered ring transition state.
Das Massenspktroskopische Fragmentierungsverhalten von Derivaten des Benzisothiazol‐S‐dioxids
Authors: Hettler H. , Schiebel H. M. , Budzikiewicz H. 
Published: May 2005

AbstractDas Fragmentierungsverhalten von Derivaten des Benzisothiazol‐S‐dioxids wird diskutiert. Es läßt sich für die Verbindungsklasse eine Reihe von typischen Zerfallsreaktionen erkennen, deren relatives Gewicht jedoch stark von der Art der substitution abhängt. Soweit dies energetisch günstig ist, tritt bevorzugt Abbau des Substituenten (evtl. gefolgt von Verlust von SO2) auf, Anderenfalls Zerfall des heteroaromatischen Ringes. (u.U. erst nach Umlagerung im Bereich der SO2‐Gruppe). parallelität zwischen thermischen und elektronenstoßinduzierten Umlagerungen wird nicht beobachtet.