bluuebunny/crossref_metadata_2025 huggingface dataset:
Solvent dependence of the molecular structures of furan and thiophene determined by NMR of partially oriented molecules
Authors: Diehl P. , Jokisaari J. , Müller S. , Väänänen T.
Published: May 2005

The molecular rα structures of furan and thiophene dissolved in liquid crystals Merck ZLI 1167 and Phase IV were determined from the linear combinations of dipolar HH and CH coupling constants derived from the 1H and 1H13C satellite NMR spectra. Significant variations with the liquid crystal solvent are observed for both molecular structures. The deformations are particularly large in the case of thiophene and, surprisingly, in the normally well behaved ZLI 1167 liquid crystal.
NMR of some benzodiazepine drugs: Structure elucidation with lanthanide‐induced shifts of N‐1 substituted benzodiazepinones
Authors: Cazaux Louis , Vidal Christiane , Pasdeloup Maurice
Published: May 2005

Two 1,4‐benzodiazepinones of psychopharmacological interest, pinazepam (2) and prazepam (3), were studied in solution by 13C and 1H NMR. 1H variable‐temperature experiments showed that the seven‐membered ring exists in a simple pseudo‐boat form at room temperature, but the energy barrier is higher in 3 (ΔG405°c = 82.8 kJ mol−1) than in diazepam (1). Moreover, upon addition of LSR, the boat conformation is retained in the lanthanide ion‐substrate complex, as with 1 in the solid state. Using a concentration‐dependent shift technique and a computer‐assisted LIS method, the conformations of the N‐branched side‐chain were investigated. Two preferred orientations were found for the propargyl group of 2, while three unequally populated conformations of the cyclopropyl moiety of 3 are distributed preferentially in the sterically unhindered space around the complex.
Some INDO calculations of the dependence of one‐bond phosphorus‐phosphorus coupling upon molecular geometry
Authors: Duangthai S. , Webb G. A.
Published: May 2005

Some INDO parameterized SCPT calculations of 1J(PP) and 1J(PP) are reported as a function of geometry. At structures corresponding to the gas‐phase equilibrium configuration of diphosphine, all of the substituted diphosphines considered are predicted to have negative values of 1J(PP). Both contact and non‐contact contributions to 1J(PP) are significant, whereas the angular variation of 1J(PP) is mainly due to the contact term. The non‐contact interactions are dominant in determining the value of 1J(PP).
Determination of acid dissociation constants of histidine‐containing peptides by proton magnetic resonance spectroscopy
Authors: Giralt Ernest , Viladrich Roser , Pedroso Enrique
Published: May 2005

The acid dissociation constant of the imidazolium ring of the decapeptide luliberin has been determined by 1H NMR‐followed titration in D2O. The normal procedure for the analysis of the titration curve, i.e. direct use of the Henderson‐Haselbalch equation, is still applicable in this case, but for more complex peptides a modified calculation procedure is proposed. Results obtained when both methods were applied to luliberin are compared. The influence of D2O when used as the solvent in this type of determination has been studied using Nα‐acetyl‐L‐histidine methyl ester as a model compound. The difference between the acid dissociation constant of this molecule determined in H2O and in D2O implies that a correction of −.25 unit is needed for those pKa values calculated by plotting the chemical shifts in D2O vs the apparent pH meter readings. The pKa found for Nα‐acetyl‐L‐histidine methyl ester, 6.30 ± 0.04, can be taken as a standard value for histidine‐containing peptides.
1H and 13C NMR spectra of 1‐palmitoyl‐2‐oleyl‐sn‐glycero‐3‐phosphorylcholine in CDCl3 solution and in sonicated dispersions in 2H2O
Authors: Santaren Juan F. , Rico M. , Ribera A.
Published: May 2005

A mixed‐acid monounsaturated lecithin, 1‐palmitoyl‐2‐oleyl‐sn‐glycero‐3‐phosphorylcholine (POL), has been synthesized by phospholipase A2 digestion of 1,2 dipalmitoyl‐sn‐glycero‐3‐phosphorylcholine followed by reacylation of the lysolecithin with oleic anhydride.

1H (90 MHz) and 13C (25.2 MHz) NMR spectra of POL in CDCl3 solution and in sonicated dispersions in 2H2O have been obtained, and spin‐lattice relaxation times measured. The relaxation times were characteristic of the type of structure formed and reflect molecular motion within the lecithin molecule in each structure. In both systems the spin‐lattice relaxation times increase along the alkyl chains towards the terminal methyl group, showing a corresponding increase in the chain molecular motion, although there are significant differences in the gradation of the changes.
Carbon‐13 NMR spectra of hydroxylated bile acid stereoisomers
Authors: Iida Takashi , Tamura Toshitake , Matsumoto Taro , Chang Frederic C.
Published: May 2005

Carbon‐13 NMR signals were assigned for the complete set of the 26 theoretically possible isomers of methyl 5β‐cholanates having one to three hydroxy groups at positions C‐3, C‐7 and/or C‐12 in the nucleus. Substituent effects on the 13C NMR shielding data serving to characterize the position and configuration of the hydroxy groups are discussed.
1H NMR spectra and conformational analysis of some 1,4‐dithiepan‐6‐ones
Authors: Cook Michael J. , Ghaem‐Maghami Ghoabad , Kaberia Festus , Bergesen Knut
Published: May 2005

1H NMR Parameters are reported for five 1,4‐dithiepan‐6‐ones. 1,4‐Dithiepan‐6‐one 1‐oxide exists in solution as an equilibrium involving two different twist‐chair conformations, which contrasts with its conformational behaviour in the solid state. Twist‐chair conformers are also adopted by other members of the series, the favoured form varying with ring substitution. The SO bond in 1,4‐dithiepan‐6‐one 1‐oxide and in its 5,5‐dimethyl analogue exhibit a preference for the pseudoaxial site.
1H NMR utilization of through‐space effects: III—configuration of oximes and analogous compounds
Authors: Rouillard M. , Girault Y. , Decouzon M. , Azzaro M.
Published: May 2005

The configurational assignment of Z and E nitrogen derivatives () of 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one was made taking into consideration the through‐space effects on oxime, O‐methyloxime, dimethylhydrazone, tert‐butylimine, N,N,N ‐trimethylhydrazonium iodide and oxime hydrochloride derivatives. The relationship between the magnitude of the chemical shifts of the α‐protons and the dihedral angle formed by the α‐CH bond and the CNOH plane was interpreted in terms of the geometrical dependence of the electric field effect. For the different Y substituents, the change in chemical shift between the Z and the E configuration of the proton near the functional group was mainly dependent on the electric field effect.
Recognition and assignment of meso and dl diastereomers: Dimethyl α,α′‐Dibromopimelate and N‐benzyl‐2,6‐dicarbomethoxypiperidine
Authors: Solladie‐Cavallo A. , Bouchet M. J. , Wermuth C. G.
Published: May 2005

The assignment of meso and dl diastereomers is carried out by NMR analysis of the signals due to the methylene protons in two simple cases, namely, dimethyl α,α′‐dibromopimelate (as an acyclic compound) and N‐benzyl‐2,6‐dicarbomethoxypiperidine (as a cyclic compound). In the case of the heterocyclic compound, an nσσ* hyperconjugative interaction between the CH bond α to the heteroatom and the lone pair of the heteroatom can be used, and leads to the same assignment.
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

The 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

The 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

The 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

The 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

2‐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

13C 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

The 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

The 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

The 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

The 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

1α,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

The 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

Two 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.
Kombination von Feldionen‐ und Elektronestoß‐Massenspektren zur Struckturbestimmung, Demonstriert am Beispiel von Monoterpenen
Authors: Beckey H. D. , Hey H.
Published: May 2005

The field ionization and electron impact mass spectra of some monoterpenes are compared. Some general rules applicable also to other substances are derived, summarizing the new structural information that can be obtained by combination of field ionization and electron impact data. The general conclusions are: (1) By comparison of FI and EI mass spectra one can recognize which of the most intense peaks in the EI mass spectra are originating from rearrangement or multistip dissociation processes on the one hand, or from simple direct bond rupture on the other hand. (2) The molecular weight of each substance containing C, H, O, N atoms (or some of them) can be determined unambiguously by field ionization, even if there is no parent peak detectable by electron impact. (3) Extremely strong metastable peaks in the FI mass spectrum are indicative of the splitting off of a polar group from a highly branched carbon atom, under rearrangement of the molecular ion. (4) Ions of about double the molecular weight are often found in the FI mass spectra if the molecule contains carbonyl or hydroxyl groups, or conjugated multiple bonds in aliphatic compounds.
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

The 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

Die 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:
magnified image
The mass spectra of some guanidines
Authors: Beynon J. H. , Hopkinson J. A. , Williams A. E.
Published: May 2005

The 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

In 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

Die 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

Competing 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

The 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

The 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.
Further insight into the mass‐spectral fragmentation of tetracyclone. Tetraphenyltetrahedrane ion
Authors: Bursey Maurice M. , Elwood Thomas A.
Published: May 2005

The p‐fluoro labeling technique is used to demonstrate that the ions formed by the loss of CO from tetracyclones pass through a tetrahedral transition state or intermediate before they fragment.
The mass spectrometry of volatile derivatives—II: N‐alkyl trifluoracetamides
Authors: Saxby M. J.
Published: May 2005

Under 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

Changes 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

The 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.
Mass spectra of benzotriazinones and the first loss of 28 mass units
Authors: Tou James C. , Shadoff Lewis A. , Rigterink R. H.
Published: May 2005

Mass spectra of five benzotriazinone derivatives are reported and the fragmentation mechanisms are discussed. That the first loss of 28 mass units is a nitrogen molecule appears to be characteristic of the molecules.
The structural significance of doubly charged ion spectra. Phenylenediamine derivatives
Authors: Vouros P. , Biemann K.
Published: May 2005

The 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

The 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

The 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

The 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.
Stereoisomeric effects on mass spectra—II: The isomeric methyldecalins
Authors: Meyerson Seymour , Weitkamp A. W.
Published: May 2005

Mass spectra of the four stereoisomeric 1‐methyldecalins and the four 2‐methyldecalins have been measured. For each set of stereoisomers, the order of relative intensity of the parent‐less‐CH3 ion, but not of the parent ion, parallels the order of relative stability of the molecules. The correlation suggests that loss of the methyl group from the members of each set of stereoisomers leads to a common product, with the differing conformational energies converting into differences in vibrational energy, which in turn lead to differing extents of further decomposition.
Mass spectrometry in structural and stereochemical problems—CLXXII: The electron‐impact promoted fragmentation of 1,2‐cyclohexanediol
Authors: Strong M. Karen , Djerassi Carl
Published: May 2005

The mass spectra of 1,2‐cyclohexanediol and important data from the spectra of four deuterium labeled analogs have been recorded and mechanistic rationalizations are given for the most important degradation processes observed. Multiple mechanisms are required to explain the indicated peak shifts in the labeled analogs. Particularly relevant is the initial loss of water from the molecular ion, which involves at least four distinct processes.
Mass spectrometric studies on gibberellins
Authors: Takahashi Nobutaka , Murofushi Noboru , Tamura Saburo , Wasada Nobuhide , Hoshino Hiroko , Tsuchiya Toshikazu , Sasaki Shin‐Ichi , Aoyama Tetsumi , Watanabe Eiji
Published: May 2005

Based on the element maps of twenty‐two gibberellin methyl esters fragmentations are discussed, which are characteristic of the common structural features as well as structural modification in gibberellin homologues.
High‐sensitivity measurement of metastable ion abundances
Authors: McLafferty F. W. , Okamoto J. , Tsuyama H. , Nakajima Y. , Noda T. , Major H. W.
Published: May 2005

Measurement of metastable ion abundances over a dynamic range of 105 is possible with a specially designed mass spectrometer.
The steric effect as a mechanistic tool in mass spectral decompositions. Comments on the activated complex for the loss of no from substituted nitrobenzenes
Authors: Bursey Maurice M.
Published: May 2005

The effect of ortho substituents in nitrobenzence radical cation decompositions are discussed for non‐interacting halogen substituents. These effects are distinct from those of the same substituents in the meta and para positions, and support previous indications that ring position identity is retained in nitrobenzene molecular ions. More importantly, the steric effect of the halo substituents may be gauged from these data; it indicates that several previously suggested mechanisms for the loss of NO must be reconsidered. The existence of steric effect in very well defined systems may be used as a structural tool in organic mass spectrometry.
Relative free radical stabilities from α‐cleavage of β‐substituted N‐ethylanilines
Authors: Shapiro Robert H. , Turk Jonathan
Published: May 2005

This paper describes a direct appearance potential difference method, which is employed to determine, qualitatively, relative free radical stabilities. The method appears to be of general value since the starting materials (β‐substituted N‐ethylanilines) are relatively simple to prepare and because the dominant electron‐impact reaction is the one which releases the free radical under investigation.
Skelettumlagerungen Unter Elektronenbeschuss—IV: Zur Struktur der C13H9‐ und C12H9N‐Ionen bei Benzylidenaminobenztriazolen
Authors: Rapp U. , Staab H. A. , Wünsche C.
Published: May 2005

Die Hauptfragmentierung des 1‐(Benzylidenamino‐) benztriazols führt über eine Skelettumlagerung zu dem [C13H9]+‐Ion als. 2‐(Benzylidenamino‐) bildet ebenfalls über eine Skelettumlagerung ein [C12H6N]+‐Ion von beträchtlicher Intensität. Durch Appearance potential‐Massungen wird gezeigt, daß für diese ionen eine Fluorenyl‐bzw. Carbazol‐Struktur ausgeschlossen werden kann.
Field ionization mass spectrometry—II: Benzyloxycarbonyl and t‐butyloxycarbonyl derivatives of some simple peptides
Authors: Brown Peter , Pettit George R.
Published: May 2005

A brief discussion is given of some factors that merit consideration in the analysis of peptides by mass spectrometry, with emphasis on sequence determination. The first systematic study of simple peptides by field ionization (FI) is described, and comparison made with the corresponding electron‐impact (EI) ionization spectra, both at low resolution (approx. 1500). The substances examined were either benzyloxycarbonyl or t‐butyloxycarbonyl derivatives of di‐through pentapeptide methyl esters, containing the amino acids glycine, alanine, leucine, serine, threonine, proline and tyrosine. The incidences of sequence‐characteristic cleavage peaks and rearrangement ion peaks were both slightly lower in the FI than the EI spectra, although the peak relative intensities generally were higher under FI conditions.
Analysis of organic salts by laser ionization
Authors: Vastola F. J. , Mumma R. O. , Pirone A. J.
Published: May 2005

Alkali salts of 1‐hexyl sulfonate were ionized by laser irradiation and the positive ions were analyzed by time‐of‐flight mass spectrometry. The sodium, potassium, rubidium and cesium salts produce relatively simple spectra. The major organic ions observed are due to the salt plus a cation or the dimer plus a cation. No molecular or fragment ions were detected. The instrumentation and the method of interpreting these data are described.
The effect of substituents on the average internal energy of benzoyl ions generated from N‐(substituted‐phenyl)benzamides
Authors: Shapiro Robert H. , Turk Jonathan , Serum James W.
Published: May 2005

The [56.5*]/[105]+ ratios observed in the spectra of N‐(nitrophenyl)benzamides are greater than those observed in the spectra of N‐(methoxyphenyl)benzamides. These results differ from those observed in the spectra of monosubstituted benzophenones. An explanation, based on energy distribution and breakdown curves, is employed to rationalize these results, as well as other phenomena reported in the literature.
Correlation of the mass spectral and photochemical behavior of some 1,3‐dieneiron tricarbonyl complexes
Authors: Dauben William G. , Lorber Milton E.
Published: May 2005

The mass spectra of a number of 1,3‐dieneiron tricarbonyl complexes have been investigated. It has been shown that complexes derived from substituted 1,3‐cyclohexadienes lose hydrogen or methane in the mass spectrometer to lead predominantly to the formation of odd electron ions containing the iron atom bonded to an aromatic system. The fragmentation route followed by these complexes and those from acyclic dienes is compared.
Mass spectrometric analysis of N‐substituted cyclohexene‐1,2‐dicarboximides
Authors: Mitchell Earl D. , Waller George R.
Published: May 2005

Both low and high resolution mass spectra of cis‐4‐cyclohexene‐1,2‐dicarboximide, its N‐methyl, N‐ethyl, N‐n‐propyl and N‐n‐butyl derivatives, and cyclohexane‐1,2‐dicarboximide were obtained at 70 eV. Each of the spectra exhibited characteristic nominal ions at masses 151, 136, 123 and a group of ions at masses 77, 78, 79, 80 and 81 of which m/e 80 was always the base peak except for the unsubstituted cyclohexane compound. The m/e 77 to 81 fragments are composed of carbon and hydrogen and derived from the cyclohexene ring. The ions possessing higher masses are heterocyclic and certain of them show doublets and triplets. Evidence for a 1,3 hydrogen migration was supplied by studies with the N‐(ethyl‐2‐d3) derivative and evidence for a 1,4 migration by the N‐(n‐propyl‐3‐d3) derivative.
Mass spectrometry—II: The unimolecular decomposition of benzaldehyde azine in the gas phase induced by electron‐impact
Authors: Scheppele Stuart E. , Grigsby Ronald D. , Kinneberg Keith F. , Mitchell Earl D. , Mannan Claude A.
Published: May 2005

The mass spectra of benzaldehyde azine‐α, αA‐d2 (III) and benzaldehyde azine‐d10 (IV) reveal that both ring and α hydrogen are lost from the molecular ion of benzaldehyde azine (II) in forming the [M –1] ion. Data from the spectra of III and IV at 70 eV and reduced ionizing voltages are consistent with the existence of two competing pathways producing [M –1] ions. Rearrangement ions are observed in the spectra of II. Randomization is unimportant in the electron‐impact‐induced fragmentation reactions of II. The rearrangement‐fragmentation reactions for II in general parallel those previously observed for acetophenone azine (I).
The mass spectra of diaziridinones
Authors: Lengyel István , Greene Frederick D. , Pazos José F.
Published: May 2005

The electron‐impact induced fragmentation of four N,N′‐di‐t‐alkyl‐substituted diaziridinones (I to IV) has been studied by both conventional and high resolution mass spectrometry. All diaziridinones exhibit weak molecular ions. Ejection of an alkyl isocyanate, corresponding to the N‐alkyl substituent, from the molecular ion, is a dominant and general fragmentation process. Isocyanate‐type odd‐electron fragment ions occur only in III and IV (where at least one R group is phenyl) and are of low abundance. Elimination of a hydrocarbon radical from the tertiary alkyl substituents is observed in all compounds investigated. McLafferty rearrangement with elimination of a neutral alkene occurs in all compounds. Abundant even‐electron hydrocarbon ions corresponding to the mass of the N‐alkyl substituent are prevalent. The complete absence of elimination of carbon monoxide is noted. Loss of oxygen from the [M  RCH2]+ species has been confirmed by accurate mass measurement. Several remarkable rearrangement reactions have been uncovered by high resolution studies and deuteration experiments.
Ortho‐rearrangement in the mass spectra of diphenylmethanes
Authors: Scott Ward M. , Wacks Morton E. , Steelink Cornelius , Fitzpatrick J. D.
Published: May 2005

The mass spectra of all possible methyl substituted derivatives of 3,3′,5,5′‐tetramethyl‐4, 4′‐dihydroxy‐diphenylmethane are recorded. The direct influence of steric hindrance to free rotation about the aryl‐methylene bonds results in the progressive importance of ortho‐rearrangement in the ionization‐dissociation pathways of these compounds.
Mass spectra of nucleoside derivatives
Authors: Dolhun J. J. , Wiebers J. L.
Published: May 2005

The mass spectra of derivatives of uridine, adenosine, cytidine and guanosine are recorded. Derivatization techniques include permethylation, acetylation, trifluoroacetylation, trimethylsilylation and the synthesis of 2′,3′‐O‐isopropylidenes and 2′,3′‐O‐phenylboronic esters. Sequential derivatization by a selective combination of some of these procedures results in nucleosides which are blocked with a characteristic group at the cis 1,2 diol position, and, which contain other substituent groups that enhance the volatility of the compound. The specific substitution at the cis‐glycol region has been shown to be particularly useful in asymmetrically derivatizing dinucleoside phosphates since certain fragment ions from their mass spectra indicate the sequence of the two nucleoside components. Sequence isomers such as adenylyl‐(3′‐5′)‐uridine and uridylyl‐(3′‐5′)‐adenosine can be unambiguously distinguished.
Spectrométrie de Masse—IV: Fragmentation des Dicétones—ϵ
Authors: Kossanyi Jean , Mogto Josué Kom
Published: May 2005

La dégradation induite par bombardement électronique de dix dicétones‐ϵ symétriques a été investiguée; une rationalisation des mécanismes de fragmentation, confirmée par deutération, a pu étre proposée pour expliquer les dégradations observées. La transposition de McLafferty ne représente pas, ici, l'une des principales fragmentations bien qu'une double transposition de ce type soit présente pour les composés à chaíne longue. Une attention particuliére a été prétée aux ions résultant de la perte d'eau et de la perte d'dne molécule d'ethyléne à partir de l'ion moléculaire, pertes qui font intervenir un intermédiaire du type cyclobutanol comme dans le cas des photoisomérisations de ces composés.
Pyrolytic studies of phenoxarsine derivatives
Authors: Tou James C. , Wang C. S. , Alley E. G.
Published: May 2005

The predicted pyrolyzate of phenoxarsine derivatives from their mass spectra is diphenylene oxide. The prediction is verified by the experiment.
Electron‐impact studies of ms‐porphyrins
Authors: Adler A. D. , Green J. H. , Mautner M.
Published: May 2005

The mass spectra of several ms‐porphyrins and their metalloderivatives have been obtained on an AEI MS‐902 mass spectrometer. The main features of these spectra are very stable parent peaks and relatively abundant doubly‐charged and triply‐charged fragments. Metal substitution has a drastic effect on the fragmentation pattern, which discloses formation of fragments with a stable composite π‐electron ring, including Hückel rings. Ion‐molecule reactions giving products up to [M + 124]+ are also reported.
Mass spectra of the substituted quinuclidines
Authors: Kostyanovsky R. G. , Mikhlina E. E. , Levkoeva E. I. , Yakhontov L. N.
Published: May 2005

The mass spectra of the quinuclidine‐2 (and ‐3)‐ones and other functional derivatives of quinuclidine as well as 2‐azaquinuclidine and benzoquinuclidine have been investigated. The fragmentation through the open form of the molecular ion and the applicability of Bredt's rule to amine fragmentation of the bridgehead nitrogen bicyclic systems are discussed.
Thermal and mass spectrometric fragmentation of esters of deuterated long chain carboxylic acids
Authors: Sun Kwok K. , Hayes Herbert W. , Holman Ralph T.
Published: May 2005

A method combining thermal fragmentation and mass spectrometry for the determination of the position of double bonds in an unsaturated ester is presented. The thermal fragmentation of methyl esters of deuterated long chain carboxylic acids yields a homologous series of olefins plus a homologous series of unsaturated esters. The positions of the deuterium atoms in the original ester are revealed by the deuterium content of its fragments as determined by mass spectrometry. Therefore, the positions of double bonds of a polyunsaturated acid can be determined by pyrolysis after saturation by deuterium. The structures of the unsaturated fragments are ascertained by mass spectrometric method, and the formation of the ion [M – 32] in the mass spectrometric fragmentation of unsaturated methyl esters is studied by means of deuterium labeling.
Electron‐impact promoted fragmentation of some substituted isoxazolidines
Authors: Duffield A. M. , Buchardt Ole
Published: May 2005

A series of substituted isoxazolidinylacetophenones (II to VI) have been shown to fragment subsequent to electron‐impact in a generally predictable fashion. One characteristic fragmentation of all the compounds investigated was the loss of H2O2 from their respective molecular ions.
Mass spectrometry in structural and stereochemical problems–CXCV: The structure of the [C6H6O]+˙ ion in the spectrum of phenyl alkyl ethers
Authors: Woodgate Paul D. , Djerassi Carl
Published: May 2005

The [C6H6O]+˙ ion from C6H5OC4H9 is structurally similar to the molecular ion from phenol as demonstrated by 13C labeling.