bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of allylic strain on the conformations of diphenyl‐substituted tetrahydro‐1,3‐oxazin‐2‐ones and hexahydropyrimidin‐2‐ones
Authors: Kurtev Bogdan J. , Lyapova Maria J. , Mishev Stoyan M. , Nakova Olga G. , Orahovatz Alexander S. , Pojarlieff Ivan G.
Published: May 2005

The conformations of the cis and trans isomers of 4,6‐diphenyl‐, 4,5‐diphenyl‐ and 5,6‐diphenyltetrahydro‐1,3‐oxazin‐2‐one and 4,5‐diphenylhexahydropyrimidin‐2‐one, and of some of their N‐substituted derivatives, have been studied by 1H NMR. Conformers with 4a, 6e‐, 4a, 5e‐ and 5a, 6e‐phenyl groups are preferred in the respective isomers of the N‐H oxazinones, confirming a half‐chair conformation of the ring. Allylic strain caused by N‐substituents shifts strongly the a,e⇌e, a equilibria in trans‐4,6‐diphenyl‐ and cis‐4,5‐diphenyl‐oxazinones, but only moderately the e,e⇌a,a equilibria in the compounds with trans‐vicinal phenyl groups. In the latter, the diaxial conformation is preferred only in the case of bulky N‐substituents. The diaxial conformation is more favoured in the trans‐4,5‐diphenylpyrimidones.
Application of the computer program GENOA and two‐dimensional NMR spectroscopy to structure elucidation
Authors: Lindley Matthew R. , Shoolery J. N. , Smith Dennis H. , Djerassi Carl
Published: May 2005

The effectiveness and utility of the combined use of the interactive computer program GENOA and two‐dimensional double quantum coherence 13C NMR spectroscopy to solve structure elucidation problems are demonstrated with three examples. The substructural information inferred from the 1H NMR and 13C NMR spectra was insufficient to identify the structures of the example compounds. However, with the additional substructural information available from the two‐dimensional NMR experiment (which identifies directly bonded carbon atoms), the problems were solved in an extremely efficient manner.
The shielding of H‐α in the stabilized rotameric forms of α,α‐di‐tert‐butylthioacetic esters. The electric and magnetic anisotropic effects of the thione group
Authors: Balasubrahmanyam S. N. , Bharathi S. Narasimha , Usha G.
Published: May 2005

The currently accepted geometry of carbonyl magnetic anisotropic effects, if regarded as extendable to the thione group, imply that the more deshielded of the two H‐α lines in the1H NMR spectra of α,α‐di‐tert‐butylthioacetic esters should be assigned to the ‘180° form’ in which CS is antiperiplanar to C‐αH. CNDO results, however, indicate the opposite; the line should be assigned to the ‘O° form,’ in which CS eclipses C‐αH, if the predicted considerable increase in 1s density at H‐α on going from the 0° form to the 180° form is taken into account. A change in 1s density at H‐α as a result of increased branching of alkylation at C‐α is also found. These specific effects must be taken into account when discussing the anisotropic effects of CO or CS on H‐α shifts.
The NMR spectra of porphyrins: 22—Ring current effects in chlorins versus porphyrins
Authors: Smith Kevin M. , Goff Dane A. , Abraham Raymond J. , Plant James E.
Published: May 2005

The proton NMR spectra of tetraphenylporphyrin, octaethylporphyrin and the analogous chlorins (7,8‐dihydroporphyrins) are presented, and the chemical shift changes on chlorin formation are interpreted using a ring current model. In these compounds a general 10% reduction in the ring current occurs upon chlorin formation. Similar comparison of the chemical shifts of the corresponding dications and also of the protonated form of 2‐vinylphylloerythrin methyl ester with the corresponding chlorin, methyl pyropheophorbide‐a, shows that chlorin formation now has a much larger effect on the ring current, this reflecting the increased steric effects within the macrocycle which occur upon protonation. Variable temperature studies on the porphyrins and chlorins examined show clearly the effect of NH exchange processes and, in particular, novel intermolecular exchange processes with trifluoroacetic acid in the protonated species are recorded.
Configuration and NMR study of tricyclic oxazines fused to a norbornene or norbornane skeleton
Authors: Sohár P. , Stájer G. , Bernáth G.
Published: May 2005

Tricyclic oxazines fused with norbornane or norbornane were synthesized for pharmacological and stereochemical purposes. Analogous oxazin‐2‐ones and ‐2‐thiones were also obtained. The diendo or diexo anellation of the hetero ring to the norbornene or norbornane skeleton was confirmed by 1H and 13C spectral data. The assignment of the proton signals was proved and the proton‐proton coupling values were determined by double resonance experiments. With mono‐ and dichloroacetyl chloride, the oxazines fused to norbornene gave azetidinones which are mixtures of two isomers. The mixtures were separated into homogeneous substances, the configuration and conformation of which were determined via differential NOE experiments.
Carbon‐13 nuclear magnetic resonance examination of benzonorbornene derivatives. Assignment of site of aromatic ring substitution in benzonorbornen‐2‐ones
Authors: Reitz Thomas J. , Grunewald Gary L.
Published: May 2005

13C nuclear magnetic resonance spectra were collected for a series of 5‐ and 6‐monoaromatic ring‐substituted benzonorbornadienes and 5‐, 6‐, 7‐, and 8‐monosubstituted benzonorbornen‐2‐ones. 13C chemical shifts values were found to be useful in the differentiation of the four monosubstituted aromatic ring isomers of benzonorbornen‐2‐one (1). We found that the 13C NMR spectrum of a substituted benzonorbornen‐2‐one (A) could be predicted with good accuracy (R2 for each aromatic carbon ≥ 0.925) from a knowledge of the 13C NMR spectrum of 1 and the appropriately substituted benzene. The substituents studied were NO2, NH2, I, CF3, CN, OCH3, and H. Correlation analysis showed that the carbonyl in A was effectively insulated from the ring π‐system.
1H and 13C NMR spectra of cyclic trimers, tetramers and pentamers derived from p‐substituted phenylacetylenes
Authors: Rao V. V. Ramana , Griesbaum K.
Published: May 2005

The 1H and 13C spectra of p‐substituted 1,3,5‐triarylbenzenes, 7‐ and p‐substituted 1,3,9‐triaryl‐9‐methyl‐fluorenes and 2‐, 10‐ and p‐substituted 6,12,13a‐triaryl‐12‐methylbenzo(6,7)cycloheptadieno[1,2,3‐jk]fluorenes have been examined. p‐Substituents were methoxy, methyl and fluorine groups. The 1H spectra were recorded at 300 MHz and permitted assignments for the aromatic protons by selective proton decouplings. Partial assignment of the carbon atoms in the 13C spectra was also possible.
The NMR spectra of the porphyrins: 23—Metalloporphyrins as diamagnetic shift reagents, chemical applications
Authors: Abraham Raymond J. , Bedford Geoffrey R. , Wright Brian
Published: May 2005

Some applications illustrating the use of zinc (II) meso‐tetraphenylporphyrin (ZnTPP) as a diamagnetic shift reagent are described. The complexation shifts (ΔP) in a series of substituted pyridines are shown to be determined by both the basicity of the coordinating nitrogen atom and steric effects of ortho‐substituents. The selectivity of ZnTPP (N»O) in the simplification of the spectra of multifunctional ligands is demonstrated. Addition of the reagent neither affects the rotamer populations of the Inderal side‐chain nor produces any distortion of the 2‐benzylmorpholine ring. In addition, the substrate‐reagent solution may be shaken with D2O to identify exchangeable protons. The application of ZnTPP in structural problems involving substituted imidazo[2,1‐b]thiazoles and 2‐benzyl‐1,3‐dioxopyrrolo[3,4‐c]pyridines allows unambiguous identification of the possible structural isomers. To overcome the solvent limitations of ZnTPP, the more soluble Co(III)TPPBr can be used successfully as a shift reagent in DMSO‐d6, CD3OD and acetone‐d6 solutions.
Structural studies on 9‐hydrazono‐6,7,8,9‐tetrahydro‐4‐oxo‐4H‐pyrido[1,2‐a]pyrimidines by 1H, 13C and 15N NMR spectroscopy
Authors: Tóth Gábor , Szöllösy ÁRon , Almásy Attila , Podányi Benjámin , Hermecz István , Breining Tibor , Mészáros Zoltán
Published: May 2005

1H, 13C and 15N NMR studies demonstrated that 9‐hydrazono‐6,7,8,9‐tetrahydro‐4‐oxo‐4H‐pyrido‐[1,2‐a] pyrimidlnes exist as an equilibrium mixture of Z‐E isomers in the hydrazono–imino tautomeric form having an exocyclic double bond. Proton‐catalysed Z‐E interconversion is fast. Substituent and solvent effects revealed that the decisive factors controlling the Z:E ratio are internal hydrogen bonding in the Z‐isomer, stabilization by solvation and steric interaction.
Electronegativity and linear electric field effect on γ‐anti13C chemical shifts
Authors: Duddeck Helmut , Islam Md. Rabiul
Published: May 2005

The contribution from the existence of a 1,3‐diaxial H‐α ⃛H‐γ arrangement to the γ‐anti effects of substituents X, which was previously believed to be generally shielding, is shown to be extremely dependent on the electronegativity of substituent X. In the presence of axial γ‐substituents Y, linear electric field effects appear to play a significant role if the C‐γ—Y bond is highly polarizable.
Carbon‐13 NMR spectra of chlorophyll a, chlorophyll a′, pyrochlorophyll a and the corresponding pheophytins
Authors: Lötjönen Simo , Hynninen Paavo H.
Published: May 2005

The 13C NMR spectra of C‐10 epimeric chlorophylls a and a′, pheophytins a and a′, pyrochlorophyll a and pyropheophytin a have been recorded and assigned by chemical shift comparison, by long‐range selective 1H decoupling experiments and by the examination of the fully coupled spectra. Various factors influencing the 13C chemical shifts of the chlorophyll derivatives, e.g. the coordination of magnesium to the chlorin nucleus, the effect of solvent and the steric strain at the periphery of the macrocycle, have been examined. The 13C NMR spectra of chlorophyll a measured in acetone‐d6 and tetrahydrofuran‐d8 (THF) were compared, and remarkable solvent effects on the 13C chemical shifts were observed. These effects were interpreted mostly in terms of specific chlorophyll‐solvent interactions. Different electron donor and steric properties of acetone and THF were considered to cause conformational alterations in the macrocycle, induced by the ligation of the solvent molecule(s) to the axial position(s) of the central magnesium atom of chlorophyll a. These results show that 13C NMR spectroscopy is a method of high information value for investigations of the unique electron donor acceptor (EDA) properties of the chlorophylls. The structural differences between the C‐10 epimeric chlorophylls and pheophytins were examined in terms of the substituent chemical shift (SCS) parameters for the C‐10 methoxycarbonyl group. The analysis showed that the change from the (10R) to the 10(S) configuration induces conformational alterations in the whole macrocycle which are, however, most prominent in rings IV and V. Owing to the increased steric interaction (repulsion) between the bulky substituents at C‐7 and C‐10, the peripheral strain is larger in the (10S) form, and is relieved by more pronounced deviations of rings IV and V from the macrocyclic plane compared with the (10R) form. The examination of the SCS parameters also showed that the peripheral steric strain is dissipated to a larger extent over the entire macrocycle in the Mg‐free derivatives. These results confirm the previous conclusions based on 1H NMR and CD data. The possible function of chlorophyll a′ in photosynthesis is briefly discussed.
Direct structure determination of the self‐condensation product of 1‐phenylpentane‐2,4‐dione using T1 and NOE measurements from 13C NMR spectroscopy
Authors: León V. , Espidel J. , Bolívar R. A.
Published: May 2005

The nuclear Overhauser effect (NOE) is known to depend on molecular dynamics and structure. However, in some cases the values obtained for selective homonuclear and heteronuclear NOE are much too small, considering that the nuclei involved are located within a short distance of each other in space. A quantitative treatment of the NOE values allows a clear explanation of this apparent anomaly, and allows the possibility of using T1 and NOE values measured with broad‐band proton irradiation. The corresponding relationship is useful for solving many structural problems in organic chemistry, and has the great advantage of employing the typical high resolution of fully decoupled spectra. The method was used in this work for the structure determination of the self‐condensation product of 1‐phenylpentane‐2,4‐dione, and it was concluded that the previous assignment of the 13C NMR spectrum was erroneous. An independent proof of the new assignment is given using the selective collapse of the fine structure under low‐power irradiation of the methyl protons.
The mass spectra of some alkyl and aryl oxazoles
Authors: Bowie J. H. , Donaghue P. F. , Rodda H. J. , Cooks R. Graham , Williams Dudley H.
Published: May 2005

The mass spectra of a variety of alkyl and aryl oxazoles have been determined and the spectra analyzed with the aid of deuterium labelling and high resolution mass spectrometry. In contrast to the corresponding benzenoid compounds, the mass spectra of isomeric alkyl oxazoles are distinctive and in this respect are akin to those of the corresponding pyridines. Further analogy to the pyridines is suggested by the unfavorable nature of a carbonium ion adjacent to the 2‐position and this effect may be used to locate alkyl substituents attached to the oxazole nucleus. The loss of carbon monoxide from the molecular ions of 2,5‐disubstituted oxazoles probably occurs with ring opening and migration of the C‐5 substituent (e.g.Br) to the C‐4 position.
A study of rearrangement processes in the mass spectra of substituted benzophenones which provide a guide to orientation
Authors: Ballantine J. A. , Pillinger C. T.
Published: May 2005

An investigation of the mass spectra of substituted benzophenones has shown that a number of rearrangement processes are operative. The rearrangements have been shown to involve solely theortho‐substituents to the carbonyl group and in many cases the carbonyl oxygen atom itself participates in the processes. Deuterium labelling experiments combined with data obtained from accurate mass and metastable analysis have enabled the probable mechanisms of rearrangement and fragmentation to be elucidated. An understanding of these processes should greatly assist in the location of substituents in unknown benzophenones.
The symmetry of the Ion formed by stepwise loss of CO molecules in the mass spectra of p‐benzoquinones
Authors: Elwood Thomas A. , Bursey Maurice M.
Published: May 2005

Contrary to previous suppositions, it appears that the produced by the loss of 2 CO from para‐benzoquinones passes through the symmetry of not a substituted cyclobutadiene, but rather a substituted tetrahedrane, at least for inert R. The p‐fluoro labeling technique is used to obtain this result.
Mass spectrometry of aralkyl compounds with a functional group—VII. On the structure of the ions C8H9+ from C6H5C2H4X‐ and C9H11+ from C6H5C3H6X‐compounds
Authors: Nibbering N. M. M. , De Boer Th. J.
Published: May 2005

The C8H9+‐ion, formed from the molecular ions of 2‐phenyl‐1‐bromoethane, 1‐phenyl‐1‐bromoethane and of 1‐phenyl‐1‐nitroethane by loss of the bromine atom and of the nitro group, splits off a molecule of acetylene after an almost complete randomization of hydrogens, as proved by deuteration. An eight‐membered ring structure for the C8H9+‐ion is proposed to explain these results.

By loss of the nitro group from the molecular ions of 1‐phenyl‐1‐nitropropane and of 1‐phenyl‐2‐nitropropane the well‐known phenylated cyclopropane ion3 (C9H11)+ is generated. Mass spectra of analogues, specifically deuterated in the side‐chain, show that in this ion a randomization of hydrogen atoms in the cyclopropane ring as well as a hydride transfer from the cyclopropane ring to the phenyl cation occur.
The mass spectra of some triterpenoid dehydration products
Authors: Elgamal M. H. A. , Fayez M. B. E. , Kemp T. R.
Published: May 2005

The mass spectra of ten dehydration and solvolysis products obtained from β‐amyrin and glycyrrhetic acid were studied. With the exception of those resulting from ‘backbone’ rearrangement, they exhibited conventional fragmentation due to the ring C chromophore, like the parent alcohols. Only those products with a contracted ring A suffered loss of an isopropyl radical. In the latter type, special fragmentation features were exhibited by the isopropylcyclopentene and by the isopropylidene products. These differences enabled the assignment of probable structures for two unknown derivatives.
Mass spectometry in structural and stereochemical problems—CLXVIII. Effect of fluorine substitution on the McLafferty rearrangement of aliphatic ketones.
Authors: Carpenter Wayne , Duffield A. M. , Djerassi Carl
Published: May 2005

The mass spectra of allphatic ketones are drastically altered following substitution of a trifluoromethyl entity adjacent to the carbonyl group (II and III) or attachment to the γ‐carbon atom (V). Loss of the trifluoromethyl group by α‐cleavage far exceeds the alternative elimination of an alkyl radical. Virtually complete repression of the McLafferty rearrangement process (I → a) occurs when a CF3 group is attached to the γ‐carbon atom. A fluorine atom is not transferred in lieu of hydrogen in the McLafferty rearrangement as demonstrated by the mass spectrum of 1,1,1,7,7,7‐hexafluoroheptan‐4‐one (IV). Rationalization for these results are presented as is a description of the syntheses of several hitherto unknown fluorinated ketones.
Mass spectra of organometallic compounds—VIII. Some transition metal organometallic halide derivatives
Authors: King R. B.
Published: May 2005

The positive ion mass spectra of the transition metal organometallic halide derivatives C5H5M(CO)3Cl(M  Mo or W), C7H7W(CO)2I, C3H5Fe(CO)3I, [C3H5PdCl]2, and [C5H5Mo(NO)I2]2have been investigated. Further examples of the elimination of CO and C2H2fragments were noted. In addition the following effects of particular interest were observed:

(i) Evidence in the mass spectra of the chlorides for reactions with adventitious iodine and even bromine present in the mass spectrometer; (ii) Evidence for conversion of the compounds C5H5Mo(CO)3X to the new halides [C5H5Mo(CO)X]2upon pyrolysis; (iii) Evidence for facile losses of the π‐allyl group, the iodine atom, and methyl iodide in the mass spectrum of the π‐allyl derivative C3H5Fe(CO)3I; (iv) Evidence for loss of iodine upon introducing [C5H5Mo(NO)I2]2into the mass spectrometer to give ions derived from [C5H5Mo(NO)I]2.
Mass spectra of some acyclic α,β‐unsaturated aldehydes, ketones and esters
Authors: Bowles A. J. , Brittain E. F. H. , George W. O.
Published: May 2005

The mass spectra of a series of aliphatic acyclic α,β‐unsturated aldehydes, ketones and ester have been examined. The spectra do not show evidence for McLafferty rearrangements, alkoxyl migration or for fragmentations which are dependent upon the s‐trans or s‐cis conformations of the compounds. There is some evidence for cis‐trans isomerism about the double bond.
The mass spectrometry of volatile derivatives—III: N‐aryl trifluoracetamides
Authors: Saxby M. J.
Published: May 2005

The effects of substituents on the fragmentation of N‐aryl trifluoracetamides has been investigated. The base peak in all ring‐monosubstituted derivatives is the molecular ion. Other important ions arise by loss of CF3 and COCF3 from the molecular ion, and the latter daughter ion fragments further, by loss of the aromatic substituent and by expulsion of small neutral molecules. The effects of substituents on the intensity of these ions is discussed. 1‐Phenylethyl trifluoracetamide exhibits a base peak which is the molecular ion, wheras the corresponding 2‐phenyl derivative has a molecular ion of very low intensity.
Mass spectra of π‐cyclopentadienyl‐diene cobalt complexes
Authors: Yasufuku Katsutoshi , Yamazaki Hiroshi
Published: May 2005

Many reports on the mass spectra of organotransition‐metal complexes have appeared in recent years,1 whilst there have only been a few reports on the mass spectra of transition metal olefin complexes, some metal carbonyl olefin complexes234 and π‐cyclooctenyl‐π‐cyclooctadienyl cobalt.5 Recently fragmentation paths of π‐cyclopentadienyl‐cyclooctadiene rhodium were elucidated by King.6 The present authors found metastable ions in the mass spectra of π‐cyclopentadienyl‐diene cobalt complexes as well as in the mass spectra of π‐cyclopentadienyl‐diene rhodium complexes.7.

In the present paper the authors wish to report the mass spectra of several π‐cyclopentadienyl diene cobalt complexes.
Metastable transitions in the mass spectra of fluoro‐ethylenes
Authors: Jennings K. R.
Published: May 2005

Metastable transitions in the mass spectra of six fluoroethylenes are reported. In several cases in which HF is the neutral species lost, 0.4 to 0.7 eV of kinetic energy is liberated. In two fragmentations, it is shown that the kinetic energy release is only about half the minimum energy of activation of the back reaction calculated from thermochemical data. Evidence is presented to support the view that in some cases at least, fragmentation occurs from two or more electronic states of the molecular ion.
Positive‐ion fragmentation mechanisms of some organophosphorus esters
Authors: Pritchard J. G.
Published: May 2005

The mass spectra of the dimethyl and diethyl esters of phosphonic, phosphorochloridic and phosphorochloridothioic acid have been obtained, and the main paths of decomposition of their positiveions have been compared. Losses of formaldehyde occur from positive ions of all the methyl esters. Losses of C2H3˙ radicals occur consistently from the positive ions of the ethyl esters, but diethyl phosphorochloridothioate differs in showing a principal decomposition path involving initial loss of acetaldehyde. Other details are discussed.
The mass spectra of s‐triazines
Authors: Preston P. N. , Steedman W. , Palmer M. H. , Mackenzie S. M. , Stevens M. F. G.
Published: May 2005

The mass spectra of twenty‐one s‐triazines have been interpreted. An unusual feature noted in the spectra of some of the compounds is transfer of a hydrogen atom of a side chain to a nitrogen atom of the s‐triazine ring; two such shifts are suggested as a rationale for the unusual loss of nitrogen from a hydrazide derivative. The fragmentation of triamino‐ and some diamino‐ derivatives indicates that imino tautomers play a significant role. The spectra of aryldiamino s‐triazines suggest that the site of a substituent in the aryl ring is important in some cases in directing the decomposition; some transitions have been rationalised on the basis of the juxtaposition of the substituent in relation to a nitrogen atom of the heterocyclic ring.
Ortho effects–I: Fragmentation mechanisms in some ortho‐substituted nitroarenes
Authors: Benoit F. , Holmes J. L.
Published: May 2005

The mass spectra of o‐nitrobenzoic acid, o‐nitroanisole, o‐nitrosobenzoic acid, o‐nitrobenzamide, o‐nitrobenzyl alcohol and o‐nitrosobenzaldehyde have been studied. Fragmentation mechanisms are proposed for the above compounds; their elucidation was aided by isotopic labeling with D and O18. Two ‘ortho‐effects’ are discussed; one involving H atom transfer between substituents and the other migration of an atom or group to a charge carrying vacant ortho position. The importance of nitro to nitrite conversion in molecular and fragment ions is discussed.
Zum mechanismus Massenspektrometrischer Fragmentierungsreaktionen–III: Stereospezifische Reaktionen in den Massenspektren der Methyläther cyclischer Polyalkohole
Authors: Winkler Johann , Grützmacher Hans‐Friedrich
Published: May 2005

Ein Vergleich der Massenspektren von Stereoisomeren der Polymethoxycycloalkane läßt eine deutliche Abhängigikeit von der Geometrie der Molekül‐Ionen erkennen. Die Größe des stereochemischen Effekts wird beeinflußt von der cyclischen Molekü‐Ionen. Wegen energetisch günstiger Ringspaltungen wird der Effekt durch vicinale Methoxysubstituenten aufgehoben, durch Methylsubstituenten benachbart zu Methoxygruppen vermindert.

Die wichtigsten steeochemisch kontrollierten Fragmentierungen sind Elilminierung einer Methoxygruppe als Methanol‐ oder Formaldehydmolekül aus den Molekü‐Ionen. Durch Untersuchung spezifisch mit Deuterium markierter Di‐ und Tri‐methoxycyclohexane wird gezeigt, daß beide Reaktionen mit der Übertragung eines leicht abspaltbaren H‐Atoms von einem Carbinol‐C‐Atom an das O‐Atom einer Methoxygruppen beginnen. Der Eintritt beider energetisch günstiger Reaktionen hängt davon ab, ob in den möglichen Konformationen der Molekül‐Ionen eine hinreichende räumliche Annäherung der beteiligten H‐ und O‐Atome möglich ist.

Die Stereochemische Kontrolle der Fragmentierung von 1,3‐Dimethoxycyclopentan mit dem wenig beweglichen Fünfring ist gering, die der Fragmentierung von Di‐methoxycycloheptanen mit dem flexiblen Siebenring ist von vergleichbarer Größe wie der sterische Effekt in den Massenspektren von Cyclohexanderivaten.
Mass spectra of organometallic compounds–XII: Tetraphenylcyclobutadiene derivatives
Authors: King R. B. , Efraty A.
Published: May 2005

The mass spectra of the tetraphenylcyclobutadiene complexes (C6H5)4C4Fe(CO)3, C5H5CoC4(C6H5)4 and C9H7CoC4(C4H5)4 are reported. Evidence is presented for the loss of the tetraphenylcyclobutadiene ring by a two‐step sequence involving successive losses of two (C6H5)2C2 fragments. Significant differences are observed in the fragmentations of the monopositive and dipositive molecular ions of C9H7CoC4(C6H5)4.
Mass spectrometric studies–VI: Aziridines
Authors: Porter Q. N. , Spear R. J.
Published: May 2005

The mass spectra of C‐alkylaziridines show that generally β‐cleavage is the most important fragmentation, although α‐cleavages also occur as do γ‐, and δ‐ and ϵ‐cleavages in appropriate examples. A surprising rearrangement of the β‐cleavage ions has been explained as the result of a four‐centre cyclization followed by fragmentation. Other decompositions occur via transannular cleavages with and without hydrogen transfer. α‐Cleavage appears to be the most important fragmentation of N‐alkylaziridines. N‐Phenylaziridine shows very marked 1,2‐phenyl‐migration before fragmentation.
Electron‐impact fragmentation of N‐substituted 2‐aminobenzoxazoles and 2‐aminobenzothiazoles
Authors: Ogura H. , Sugimoto S. , Itoh T.
Published: May 2005

The mass spectra of twenty‐eight N‐substituted 2‐aminobenzoxazoles and 2‐aminobenzothiazoles have been recorded and the identity of various ions in the mass spectra have been established by high resolution measurement. The molecular compound of series, benzoxazole, undergoes loss of hydrogen cyanide and carbon monoxide from the molecular ion as the most important decomposition pathways. The mass spectra of N‐substituted benzothiazoles showed a similar fragmentation as that of N‐substituted benzoxazoles.
Mass spectrometry of kaurene derivatives—I. The mass spectra of some (−)‐kauran‐16‐ols
Authors: Kalinovsky A. I. , Serebryakov E. P. , Zolotarev B. M. , Simolin A. V. , Kucherov V. F. , Chizhov O. S.
Published: May 2005

The mass spectra of nine compounds belonging to the group of (−)‐kauran‐16‐ols are reported. These compounds differ either by stereochemistry at C16 (I, II) or by the nature of the substituent at C4 (III to VIII). In all cases the most characteristic ions correspond to a process in which ring D is split off and lost as a C3H6O fragment. The nature of the substituent R1 at C4 can be deduced from such typical ions as [M  R1]+ or [M  R1  H2O]+. Kauranols epimeric at C16 show little difference in their mass spectra; the assignment of configuration at this centre may be reliable only when the spectra of both epimers are compared.
Mass spectra of 1‐phenylflavazole derivatives of monosaccharides
Authors: Dolejš L. , Veisová Z. , Farkaš J.
Published: May 2005

1‐Phenylflavazole derivatives of monosaccharides show structurally characteristic and easily interpretable mass spectral fragmentation processes. The position of the deoxy or methoxy grouping may be conveniently localized.
Chemical ionization mass spectrometry of complex molecules—VI: Peptides
Authors: Kiryushkin A. A. , Fales H. M. , Axenrod T. , Gilbert E. J. , Milne G. W. A.
Published: May 2005

The chemical ionization mass spectra of a series of simple peptides containing six or fewer amino acids have been studied. Using methane as the reactant gas we found cleavage of the peptide bond occurs in two ways, yielding either the acyl carbonium ion or the complementary ammonium ion. The observation of both types of fragments permits the determination of the amino acid sequence of the peptide. The ammonium ions provide an additional sequence determining route compared to that available from electron‐impact spectra. ‘Sequence‐determing ions,’ especially the quasimolecular ion at m/e [M+1] are usually more intense than in the electron‐impact mass spectra.
Mass spectral fragmentation studies in monomeric and dimeric coumarins
Authors: Kutney James P. , Engendorf Guenter , Inaba Tadanou , Dreyer David L.
Published: May 2005

A study on the behavior of a large number of monomeric and dimeric coumarins in the mass spectrometer is reported and discussed. The results illustrate that the observed characteristic fragmentation patterns are of considerable utility in the application of mass spectrometry to structure elucidation in this series.
Mass spectrometry of hop compounds—III. Mass spectra of substituted 1,3‐cyclopentanediones derived from hop constituents
Authors: Shaw S. J. , Shannon P. V. R. , Collins E.
Published: May 2005

The mass spectra of isohumulones (IV, V), tetrahydroisocohumulones (VI, VII), tetrahydroisohumulones (VIII) neohydroisocohumulones (XI, XII) cohumulinic acid (III), lupuloxinic acid (XV), humulinone (XIV) and related compounds are described. Ions which appear to be diagnostic for particular structures are discussed.
Field desorption mass spectrometry with high temperature activated emitters
Authors: Schulten H. R. , Beckey H. D.
Published: May 2005

The use of emitters which have been activated at high temperature in Field Ionization and Field Desorption mass spectrometry offers some important advantages over the usual emitter type activated at room‐temperature. Higher thermal stability of the microneedles is achieved and the emitters are extremely resistant to chemical attack. It becomes possible to induce a thermal fragmentation of solid compounds adsorbed on the emitter surface between room‐temperature and approximately 2000°C. The field anodes may be re‐used many times without loss of quality. The problem of mass references is solved in Field Ionization/Field Desorption‐Mass Spectrometry when high temperature emitters are used. The Field Ionization mass spectra of perfluorokerosene (PFK) and perfluorotributylamine display peaks in the mass range between m/e 50 to 800, with a resolution of up to 30000 (10% valley definition). A short description of a rapid and easy activation to produce high temperature microneedles is given.

The following abbreviations are used throughout this paper:—

HT
High Temperature

RT
Room‐Temperature

BAT
Best Anode Temperature

HR
High Resolution

MS
Mass Spectrometry/Spectrum/Spectra

EI
Electron Impact

FI
Field Ionization

CI
Chemical Ionization

FD
Field Desorption
Mass spectra and pyrolysis of some oxymethylene‐linked perfluoroaromatic compounds
Authors: Cotter J. L.
Published: May 2005

The mass spectra of four oxymethylene‐linked perfluoroaromatic compounds are reported and discussed. Proposed ion structures are substantiated by precise mass measurement. The principal fragmentation pathways involving scission of oxygen to methylene bonds are supported by appropriate metastable peaks.

Parallels between the electron‐impact and thermal behaviour of two of these compounds are noted.
A method of estimating relative kinetic shifts for mass spectral fragmentation schemes
Authors: Benezra Steven A. , Bursey Maurice M.
Published: May 2005

Availability of computer‐generated tables for the estimation of kinetic shifts by the older form of the quasi‐equilibrium theory is announced.
Chemical ionization mass spectra of amino acids and derivatives. Occurrence and fragmentation of ion‐molecule reaction products
Authors: Leclercq P. A. , Desiderio D. M.
Published: May 2005

The Chemical ionization mass spectra of free amino acids, their amides, methyl esters and Na‐acetyl derivatgives, using methane as reagent gas, are presented, The occurrence and fragmentation of ion‐molecules reaction products are discussed. A preference for a head to tail, configuration of the association complex [2M + 1]+ is postulated to esplain promienent fragmentation pathways of this complex. Interesting fragmentation pathways have been found with onithine, arginine and citrulline.
Mass spectrometric studies—II: Mass spectrometric studies of maleimides and benzaldazine adducts. Identification of solid mixtues
Authors: Tam S. W.
Published: May 2005

It has been found by mass spectrometric studies that the so‐called ‘1:1‐adduct’ formed by N‐( nbutyl)maleimide and benzaldazine, is in fact a solid mixture of one part bis‐imide L and one part benzaldazine. Bis‐imide L is one of the three stereoisomeric products obtained by the addition of two mole of N‐( n‐butyl)malemide and one mole of benzaldazine. The three stereoisomeric bis‐imides gave identical mass spectra. Mass spectra of bis‐imide M and bis‐imide M‐ d2 are discussed, and confirm the proposed structures of perhydroprazolo‐pyrazole derivatives for these 1:2‐adducts.
The fragmentation of ortho‐methoxyphenyl‐2‐propanone oximes and related compounds–further examples of an ortho‐effect
Authors: Coutts R. T. , Malicky J. L.
Published: May 2005

An [M  31]+ ion was a prominent fragment in the mass spectra of three ortho‐methoxy‐phenyl‐2‐propanone oximes and is shown to be due to the expulsion of a methoxyl radical from the molecular ion as a result of an ortho‐effect. In contrast, an [M  31]+ ion was absent from the spectra of a structurally related ketone and a hydroxylamine, and was not observed in the spectra of meta‐ and para‐methoxyphenyl‐2‐propanone oximes.
Etude en Spectrometrie de Masse d'une Serie d'Anhydride du Type Acetoxy‐3 Bicyclo[2.2.2]octene‐2 Dicarboxylique‐5,6
Authors: Cassan J. , Geribaldi S. , Torri G. , Azzaro M.
Published: May 2005

Une série d'anhydrides du type acétoxy‐3 bicyclo[2.2.2]octéne‐2 dicarboxylique‐5,6 ne différant que par des substituants hydrocarbonés, a été étudiée en spectrométrie de masse é I'aide de la haute résolution. Les spectres de cette série sont complexes et ne différent que par la présence de certains pics et par des intensités relatives variables. Par des mécanismes classiques, nous avons pu expliquer la presque totalité des pics. Nous nous sommes appuyés sur les mécanismes observés dans une série analogue1,2 de bicyclo‐[2.2.2]octéne‐2 étudiée par Cimarusti et Wolinsky. On retrouve le méme schéma directeur quels que soient les substituants et les positions relatives de ceux‐ci.
Mass spectrometry of stable free radicals—II: pyrrolidine nitroxides
Authors: Davies A. P. , Morrison A. , Barratt M. D.
Published: May 2005

3‐Substituted‐2,2,5,5‐tetramethylpyrrolidine nitroxides are stable free radicals used extensively in the synthesis of ‘spin labels’. The high resolution mass spectra of these nitroxides substituted with CH2OH, OH, NH2 and o have been recorded on magnetic tape and the elemental compositions of the ions calculated by computer. Ionisation by electron bombardment(70eV), gives rise to an even‐electron molecular ion species. [M+1]+. ions are observed in the spectra of all compounds examined, except in the case of the 3‐carbonyl compound, 2,2,5,5‐tetramethylpyrrolid‐3‐one‐1‐oxyl. Loss of a methyl radical from these ions leads to the appearance of ions at [M ‐14]+. The predominant fragmentation for those compounds in which the substituents can supply electrons to the ring, is the sequential elimination of isobutene, nitric oxide and a hydrogen radical. In the case of the 3‐hydroxy compound, these ions account for 23 percent of the total ion current.

2,2,5,5‐Tetramethylpyrrolid‐3‐one‐1‐oxyl, which bears an electron‐withdrawing substituent gives rise to a fragmentation pattern somewhat different from those of the other compounds. The main features are the absence of a peak at [M + 1]+˙ and the general phenomenon of fewer peaks but with higher intensities.
Electron‐impact‐induced fragmentation of some diterpenoid acetals
Authors: Cambie R. C. , Preston A. F. , Woodgate P. D.
Published: May 2005

Study of the low and high‐resolution mass spectra of a series of diterpenoid acetals, including both positional isomers and stereoisomers, has permitted the proposal of some characteristic fragmentation pathways leading to analytically distinctive peaks. The mass spectrum was particularly informative in the assignment of structure to an unexpected rearrangement product (V).
Mass spectrometry in structural and stereochemical problems‐CCXXIX: Electron‐impact‐induced fragmentation of boric acid esters
Authors: Hammerum Steen , Djerassi Carl
Published: May 2005

The mass spectral decompositions of cyclic and acyclic borates have been examined. Straight chain trialkyl borates fragment by CO cleavage reactions accompanied by transfer of one or two hydrogen atoms, whereas tri‐(sec‐alkyl) borates primarily undergo α‐cleavage reactions. Both types of cleavage are observed in the fragmentation of cyclic borates. BO bonds are not broken in the formation of most major fragment ions. The fragmentations of borates are compared with those of phenylboronates with special emphasis on the rearrangements leading to hydrocarbon ions in the spectra of the latter.
Metastable peaks in a mass spectrum measured automatically under high resolution fast scan conditions
Authors: Carrick Alan , Paisley H. M.
Published: May 2005

Three metastable peaks have been automatically recorded in the fast scan high resolution mass spectrum of 2‐hydroxy‐4‐octoxybenzophenone. Values for released kinetic energy in the transitions m/e 326 to 325 and m/e 214 to 213 agree with the results obtained by conventional means.
Massenspektrometrie von Silylpyrazolen—I: Isomere Trimethylsilylpyrazole
Authors: Birkofer L. , Franz M. , Schmidtberg G.
Published: May 2005

Durch Vergleich der Massenspektren von isomeren Mono‐, Bis‐ und Tris(trimethylsily)pyrazolen

Die Trimethylsilyl‐Gruppe (CH3)3Si‐wird im folgenden mit TMS bezeichnet.

lassen sich charakteristische Einflüsse der verschiedenen TMS‐Gruppen ableiten. Eine N‐TMS‐Gruppe liefert bei N‐TMS‐pyrazol ein Ion m/e 72 und führt bei mehrfach silylierten Pyrazolen zur Abspaltung eines neutralen Fragmentes C3H8Si. Eine 4‐TMS‐Gruppe zeichnet sich durch bevorzugte Fragmentierung und somit durch eine geringe Molpeak‐Intensität (c.5%Σ40) aus. Eine intensive HCN‐Eliminierung aus dem [M  CH3˙]+‐Ion zeigt bei N‐silylierten Pyrazolen, die keine 4‐TMS‐Gruppe besitzen, ein unsubstituiertes C‐3‐Atom an. Für nicht N‐silylierte unsymmetrisch substituierte Pyrazole ist eine Aussage über das vorherrschende Tautomere nach silylierung mit eine N‐Trimethylsilylacetamid möglich.
The mass spectra of 1,6‐dibromo‐1,6‐dideoxyhexitols
Authors: Jarman M. , Tamás J.
Published: May 2005

The mass spectra of 1,6‐dibromo‐1,6‐dideoxy‐D‐mannitol and its O‐deuterated analogue were rationalised in terms of the number and location of the bromine and hydroxy substituents on the carbon chain.
The mass spectrometry of four acyl derivatives of 2,2′‐difurylmethane
Authors: Ferretti Aldo , Flanagan Vincent P. , Ruth John M.
Published: May 2005

Low resolution mass spectra and high resolution data for selected important peaks are presented and discussed for the following compounds: [(5‐acetyl‐2‐furyl)‐(2′‐furyl)]methane (I), [(5‐acetyl‐2‐furyl)‐(5′‐methyl‐2′‐furyl)]methane (II), [(5‐formyl‐2‐furyl)‐(2′‐furyl)]methane (III) and [(5‐formyl‐2‐furyl)‐(5′‐methyl‐2′‐furyl)]methane (IV). The fragmentation of II has been clarified by examining the mass spectrum of its d3‐acetyl analog; the fragmentation of III and IV by examining the spectra of their carbonyl 13C‐labeled analogs.
Mass spectrometry of pyrylium salts. Free radical evaporation
Authors: Hvistendahl Georg , Györösi Peter , Undheim Kjell
Published: May 2005

From ionisation potential measurements it is shown that 2,4,6‐triphenylpyrylium and thiopyrylium cations are thermally reduced in the mass spectrometer to the corresponding free radicals during evaporation of the bromides, iodides and fluoroborates. For the fluoroborates minor amounts of a fluoride adduct were also present. Perchlorate salts led to oxidation. The gaseous species from 2,6‐diphenyl‐4‐methylpyrylium iodide consists of the anhydro base and hydrogen iodide.
The mass spectrometry of 1,3,4‐thiadiazolines
Authors: Wolkoff Peder , Hammerum Steen
Published: May 2005

The mass spectra of di‐, tri‐ and tetraaryl substituted 1,3,4‐thiadiazolines have been examined. They are characterized by thiadiazolium ions, formed by elimination of a C‐5 substituent, by ions formed through elimination of C6H5S˙ radicals arising by transannular phenyl migration and by ions generated via elimination of thiocarbonyl neutrals in retro‐1,3‐dipolar cycloaddition reactions. The influence of the stability of the dipolarophile on the latter reaction is discussed and the fragmentation reactions of thiadiazolines and oxadiazolines are compared.
Chemical ionization mass spectrometry. i‐Butane reactant gas modified by ethanolamine or ethylenediamine
Authors: Bowen D. V. , Field F. H.
Published: May 2005

1,2‐Diaminoethane and 2‐aminoethanol‐1 were added to the isobutane plasma of a chemical ionization mass spectrometer. The resulting reactant gas mixture did not react with additives containing a single oxygen functional group. Addition reactions were observed with some additives containing multiple oxygen functions. Additives containing nitrogen functions were protonated by the reactant mixture. The relative proportion of protonation to addition depended on the ability of the additive to chelate the reactant ion and on the basicity of the additive. This use of 1,2‐diaminoethane and 2‐aminoethanol‐1 provides a convenient method of varying the reactivity of the plasma in a chemical ionization source.
Mass spectrometry of 2‐substituted‐1‐keto‐3‐aryl‐5H‐imidazo‐(1,5‐a)‐pyrroles derived from Schiff bases of N‐terminal prolyl peptides
Authors: Hamilton R. E. , Patil G. V. , Jayasimhulu K. , Day R. A.
Published: May 2005

We have been able to extend the use of Schiff base derivatives in peptide sequencing to N‐terminal prolyl peptides. Earlier studies from this laboratory revealed that certain aromatic Schiff bases of peptide esters gave electron‐impact mass spectra with relatively intense molecular, sequence and internal fragment ions. We observed that the reaction of N‐terminal prolyl peptide esters with 4‐dimethylaminonaphthaldehyde, p‐dimethylaminobenzaldehyde and 2‐pyridinecarboxaldehyde gave cyclization products which were found to be 2‐substituted‐1‐keto‐3‐aryl‐5H‐imidazo‐[1,5‐a]‐pyrrole derivatives. The molecular ion and many of the expected cleavages were prominent in the mass spectra. Deuterium labeling at the α‐carbon, amide nitrogen, or other exchangeable positions has been used in assigning the structure. It was also confirmed by the fragmentation pattern of the products derived by permethylation of the peptide derivative with tetramethylammonium hydroxide. Comparable cleavage patterns were seen among the N‐terminal prolyl peptides examined. Proline amide gave the corresponding cyclized product. With the inclusion of N‐terminal prolyl peptides in the list of peptides that we have examined, we may now prepare volatile derivatives of peptides containing any of the protein amino acids in two steps: esterification and treatment with the appropriate aromatic aldehyde.
Mass spectra of B, B′‐disubstituted bis(amino)diboranes(4)
Authors: Hancock Kenneth G. , Uriarte Anthony K.
Published: May 2005

The mass spectra of five B,B′‐disubstituted derivatives of the bis(amino)diboranes(4). Most of the fragmentations postulated have a precedent in similar processes of isoelectronic and/or isopolar species and are supported by the occurrence of metastable peaks.
Elektronenstossinduzierte Fragmentierung von Acetylenverbindungen. IX—Struktur der Stabilen [C9H11]+‐Ionen aus Isomeren C9H11‐Chloriden
Authors: Köppel Claus , Schwarz Helmut , Bohlmann Ferdinand
Published: May 2005

Die Struktur der stabilen [C9H11]+‐Ionen aus verschiedenen Modellverbindungen der Summenformel C9H11Cl wird mit Hilfe energetischer Messungen untersucht. Es wird ferner gezeigt, daß Acetylenverbindungen im Bereich der Auftrittspotentiale zu aromatischen Ionen cyclisieren.
Mass spectrometry of onium compounds. XXI—Substituent effect on the evaporation of anilinium oxides
Authors: El‐Mouafi Hamdi M. R. , Hvistendahl Georg , Undheim Kjell
Published: May 2005

The ionisation potentials and characteristic fragmentations of a series of anilinium oxides and their isomeric ethers have been used to assign structures for the gaseous species from the zwitterions. Transmethylation and direct evaporation of the zwitterions are competing processes. A bulky substituent ortho to the oxygen or a strongly electron attracting group in the 2‐isomer will prevent or reduce the transmethylation. If the volatility is much reduced, however, the temperature increase for evaporation results in transmethylation. The 4‐isomer was transmethylated even with two tert‐butyl groups ortho to the oxygen. The appearance potentials for an isomeric pair showed the energy difference between the zwitterion and the ether in the gas phase to be 11.5 kcal/mol.
Chemical ionisation mass spectra of explosives
Authors: Gillis R. G. , Lacey M. J. , Shannon J. S.
Published: May 2005

The chemical ionisation mass spectra of a number of representative explosives have been obtained using hydrogen as reagent gas. Fragmentation modes of the protonated molecular ions tend to be simple although some rearrangements have been noted. Loss of a radical from an even electron parent ion has been observed. The use of ‘ghost spectra’ for confirmation of the molecular weight of the sample is stressed: these consist of ions of low abundance resulting from reactions between sample ions and sample molecules. Labelling studies were carried out using deuterium as reagent gas.
Massenspektren Alicyclischer Verbindungen. IV—Die Massenspektren der Thiacycloalkanone und der Thiacycloalkanon‐1,1‐Dioxide
Authors: Herzschuh Rainer , Remane Horst
Published: May 2005

Die elektronenstoßinduzierte Fragmentierung einer Reihe von 1‐Thiacycloalkanonen und 1‐Thiacycloalkanon‐1.1‐dioxiden mit 5 bis 8 Ringgliedern wurde untersucht. Die Ergebnisse wurden mit denen des Fragmentierungsverlaufes in den Cycloalkanonen, in den Thiacycloalkanen und in den 1‐Thiacycloalkan‐1.1‐dioxiden verglichen. Es Zeigte sich, daß in den Thiacycloalkanonen der bevorzugte Ort der Ladungslokalisierung der Schwefel ist.
Common electron‐impact fragmentations of 2‐methoxy‐8,9‐dehydroadamantane and 2‐exo‐methoxyprotoadamantene
Authors: Murray Roger K. , Jelus Barbara L. , Babiak Kevin A.
Published: May 2005

2‐Methoxy‐8,9‐dehydroadamantane and 2‐exo‐methoxyprotoadamantene undergo common electron‐impact fragmentations at 70, 20 and 14.3 eV.
Isomerisation of hydrocarbon ions:I—Isomeric octanes: Acollisional actiation study
Authors: Levsen K.
Published: May 2005

The molecular ions of isomeric octanes retain their structural identity, while their alkyl fragments [CnH2n+1]+ (n = 3 to 7) isomerise to common structures prior to decomposition. Structures for [C6H13]+ and [C7H15]+ ions are proposed.
Mass spectrum and heat of formation of isocyanic acid. Production of [hco]+ from discrete electronic state of molecular ion
Authors: Compernolle F.
Published: May 2005

The appearance potentials for the transition ([HNCO]+·→ [HCO]+ + N), determined for the reaction in the ion source and in the first field free region (15·84 and 15·52 eV) correspond, respectively, to the vertical and adiabatic third ionisation potential of HNCO, as determined by photoelectron spectroscopy. The formyl ion and nitrogen radical are formed in the ground state, which requires predissociation of a quartet molecular ion of HNCO.

A heat of formation δHf(HNCO)g = −25 ± 3 kcal mol·1 was determined from the appearance potential and kinetic energy release for the metastable ion [HCO]+, and from the difference in appearance potentials for the ion [NH]+· produced from the isoelectronic molecules HNCO and HN3.