Reaktionen von Glutaminsäuredimethylester im Massenspektrometer. 21. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen

The mass spectral fragmentation of dimethyl glutamate ( 1 ) and its deuterated derivatives 1a , 1b and 1c has been investigated. By loss of a methoxycarbonyl group from the molecular ion an ion of m/e 116 is generated. The latter splits off methanol (m*), the resulting fragment of m/e 84 giving raise to the base peak of the spectrum. Only part of the hydrogen transferred to the leaving group originates from thc amino group, as was suggested earlier [2] [3]. Basing on experiments with deuterated compounds we propose an additional mechanism for the reaction, i.e. hydrogen transfer from C(3) to methoxyl. The fragment generated by both processes is most likely to be a pyrrolinonium ion. Thermal side reactions in the mass spectrometer (formation of pyroglutamic acid ester) followed by fragmentation may lead to the same ion. – The mechanisms discussed are supported by the mass spectral fragmentation of N-acetyl-glutamic acid diesters 3 , 3a , 3b and 3d and of the N, N-dimethyl derivatives 4 and 4a . – The fragmentation reactions investigated are similar to some of 1,3-trimethylenediamine derivatives [7]. This means that there are parallels in the mass spectral fragmentation of difunctional compounds irrespective of the nature of the functional groups.     

o-nitroaniline derivatives. IV—The mass spectra of o-nitroanils

The principal feature of the mass spectra of o-nitroanils, ArCH?NC₆H₄NO₂(o-), is an intense peak corresponding to the [ArCO]⁺ ion; this implies oxygen transfer from the nitro group to the azomethine carbon during the fragmentation process. In this series of anils, loss of OH from the molecular ion is not apparently an important fragmentation pathway, in contrast to the fragmentation of o-nitrobenzylideneanilines. Benzylideneaniline derivatives with an o-nitro substituent in both rings have mass spectra which indicate interaction of both nitro groups with the ? CH?N? group, but in this series of spectra the [M—17]⁺ ion is again of low intensity.     

Application of the indo molecular orbital method to ortho effects in mass spectra. Cleavage of cis-β-methoxystyrene

The principal fragmentation of the cis-β-methoxystyrene molecular ion is loss of the methyl group. Although this compound has a π system similar to that of phenyl acetate, the substituent effect of a strongly electronegative ortho substituent is insignificant for this fragmentation; but for the same substitution in phenyl acetate, it had been shown to be important. The INDO method was used to show that bond orders confirm the lack of the substituent effect in the cis-β-methoxystyrene system.     

Der massenspektrometrische Zerfall isomerer Diacetamido-cyclo-hexane,ihrer N-Phenäthyl-Derivate und Bis (acetamidomethyl)cyclohexane. 32. Mitteilung über massenspektrometrische Untersuchungen,,

The Mass Spectral Decomposition of Isomeric Diacetamido-cyclohexanes, their N-Phenethyl-Derivatives and Bis(acetamidomethyl)cyclohexanes In the mass spectra of the six isomeric diacetamidocyclohexanes 2--4 (cis and trans each, Scheme 2) as well as of the six isomeric bis(acetamidomethyl)cyclohexanes 6--8 (cis and trans each, Scheme 5) are clear differences between the constitutional isomers, whereas cis/trans isomers show very similar spectra. The lack of stereospecific fragmentations is explained by loss of configurational integrity of the molecular ion before fragmentation. However, the mass spectral fragmentation of epimeric diamidocyclohexanes becomes very stereospecific by the introduction of a phenethyl group on one of the nitrogen atoms: this group avoids epimerization of the molecular ion prior to fragmentation. In the N-phenethyl derivatives 10, 11, 13 and 14 (Scheme 8) the typical fragmentations of the cis-isomer after loss of ·C₇H₇ from the molecular ion are the elimination of CH₂CO by formation of cyclic ions, and the loss of p-toluenesulfonic acid or benzoic acid, respectively, with subsequent elimination of CH₃CN (Scheme 9). In the trans-isomer the typical fragmentations are the loss of the side chain bearing a tertiary nitrogen atom, and the elimination of the tosyl or benzoyl radical, respectively, with subsequent loss of CH₃CONH₂ (Scheme 10).     

Thienoquinolines: X—The fragmentation of thieno(2,3-b)quinoline and its derivatives under electron impact

A study has been made of the fragmentation upon electron impact of thieno(2,3-b)quinoline and sixteen of its derivatives containing methoxy, methylenedioxy, chloro, bromo, iodo, nitro and methyl substituents. Besides these, the fragmentation patterns of some S-oxides, and S,S-dioxides were also investigated. The majority of the spectra contain molecular ions and the principal fragmentation routes involve loss of carbon monosulphide and hydrogen cyanide from the molecular ion. Rearrangement of the molecular ion appears to precede the fragmentation process in the case of S,S-dioxides. The fragmentation of 4-methylthieno(2,3-b)quinoline is closely analogous to that of alkylquinolines. The main features of these spectra can be predicted from the fragmentation pathways proposed for the parent thieno(2,3-b)quinoline.     

Fragmentation characteristics of hydroxycinnamic acids in ESI‐MSn by density functional theory

This work aims to analyze the electrospray ionization multistage mass spectrometry (ESI‐MSⁿ) fragmentation characteristics of hydroxycinnamic acids (HCAs) in negative ion mode. The geometric parameters, energies, natural bond orbitals and frontier orbitals of fragments were calculated by density functional theory (DFT) to investigate mass spectral fragmentation mechanisms. The results showed that proton transfer always occurred during fragmentation of HCAs; their quasi‐molecular ions ([M − H]⁻) existed in more than one form and were mainly with the lowest energy. The fragmentation characteristics included the followings: (1) according to the different substitution position of phenolic hydroxyl group, the ring contraction reaction by CO elimination from benzene was in an increasingly difficult order: m‐phenolic hydroxyl > p‐phenolic hydroxyl > o‐phenolic hydroxyl; and (2) ortho effect always occurred in o‐dihydroxycinnamic acids (o‐diHCAs), i.e. one phenolic hydroxyl group offered H⁺, which combined with the other one to lose H₂O. In addition, there was a nucleophilic reaction during ring contraction in diHCAs that oxygen atom attacked the carbon atom binding with the other phenolic hydroxyl to lose CO₂. The fragmentation characteristics and mechanism of HCAs could be used for analysis and identification of such compounds quickly and effectively, and as reference for structural analogues by ESI‐MS. Copyright © 2017 John Wiley & Sons, Ltd.     

Electron ionisation mass spectral studies of bridgehead‐fused Δ2‐norbornanethiazolines

The electron ionisation (EI) mass spectra of a series of bridgehead‐fused Δ²‐norbornanethiazolines, a new class of bridgehead‐norbornane derivatives, have been studied and their cleavage mechanisms rationalised on the basis of the substituent shifts as well as on the identification of relevant peaks through accurate mass measurements and collision‐induced dissociation tandem mass spectrometric experiments. The fragmentation patterns of isomeric pairs of 6,6‐ and 10,10‐dimethylnorbornanethiazolines are almost identical, probably due to an initial isomerisation of molecular ion previous to the fragmentation. In general, the dominant peaks in the spectra of all the studied compounds originate from initial α‐cleavages of C(5)–C(6) or C(1)–C(10) bonds, followed by concomitant homolytic cleavage of C(1)–C(9) and C(7)–C(10) bonds. The driving force for this fragmentation pathway, directed by the gem‐dimethyl group, is the formation of a highly stabilised thiazolilmethyl cation which constitutes the base peak in all the spectra and allows the identification of these interesting ligands. Copyright © 2009 John Wiley & Sons, Ltd.     

New fragmentation pathways in the electron impact mass spectrometry of derivatized pyrano-1,3-diphenylprop-2-enones

The fragmentation patterns of closely related chalcones, cinnamoylchromans and cinnamoylchromenes, are reported to be strikingly different. The mass spectra of the first group show peaks typical of the fragmentation of simple chalcones balanced by additional fragmentation routes competing effectively with the typical chalcone fragmentation. For the other group with the introduced double bond the fragmentation is considerably changed. Initial loss of a methyl group gives rise to formation of the base peak in three of four examples. The [M – CH₃]⁺ ion decomposes further, eliminating a styrene yielding the m/z 187 ion. This process may be rationalized as a retro-Diels–Alder fragmentation of a flavanone formed on intramolecular rearrangement of the molecular ion.     

Substituent effects in mass spectrometry—II. The effect of substituents on the dissociation of para and meta disubstituted benzenes

The effect of substituents on the activation energy for primary dissociation processes in the molecular ions of mono- and para and meta di-substituted benzenes has been examined. Where the daughter ion retains the substituent group, variation of the energy of activation derives from a combination of the effects of substituents on the ionisation potential of the molecular ion and the appearance potential of the daughter ion. An equation relating the energy of activation for the fragmentation of the molecular ion of a mono-substituted benzene to that of related para and meta di-substituted benzenes is presented.     

Analogie Photochimique. II—Cyclisation des Aldéhydes δ,ε Insaturés sous Impact Electronique

The mass spectra of 4, 4-dimethyl δε-unsaturated aldehydes show an ion at m/e 126 which results from the elimination of a neutral olefin directly from the molecular ion. This fragmentation is shown to occur through a cyclohexanone intermediate involving a process whcih has its equivalent in the photochemistry of these aldehydes. The abundance ratios of the unimolecular metastable decompositions of these m/e 126 ions are in excellent agreement with the proposed mechanism.     

Ortho effects in organic molecules on electron-impact I—Oxidation of olefinic double bond by the ortho nitro group in stilbazoles

The electron-impact-induced fragmentation in 2′-nitro-4-stilbazole is triggered by the oxidation of the olefinic double bond by the ortho nitro group in the initial step, while such an interaction under the same condition is totally absent in the meta and para isomers. The important fragmentation in 2′-nitro-2-stilbazole is the formation of a cyclised ion with the elimination of the nitro group.     

The mass spectra of carboxylic acids—I: Fragmentation mechanisms in maleic and fumaric acids and related compounds

The mass spectra of maleic acid, maleic acid-2,3-d, fumaric acid and fumaric acid-2,3-d have been examined and fragmentation mechanisms are proposed for these compounds. The molecular ion of the cis-acid fragments via H atom transfer from one carboxyl group to the other followed by loss of CO₂. The trans acid does not fragment significantly by this route and the former effect may be characteristic of molecules containing two carboxyl groups cis-oriented to each other. This hypothesis was successfully tested by examining the mass spectra of citraconic, itaconic and phthalic acids. Itaconic and mesaconic acids show some of the fragmentation characteristics of fumaric acid.     

Mass spectra of new heterocycles: IX. Main fragmentaion laws of 7-methyl-2-(methylsulfanyl)-3-(1-ethoxyethoxy)-4,5-dihydro-3<Emphasis Type="Italic">H</Emphasis>-azepine and its structural isomers (2,3-dihydropyridine,pyrrole, thiophene) under electron impact

Mass spectra were investigated for the first time of four structural isomers of heterocycles, formerly inavailable 7-methyl-2-(methylsulfanyl)-3-(1-ethoxyethoxy)-4,5-dihydro-3H-azepine, 2,2-dimethyl-6-(methylsulfanyl)-5-(1-ethoxyethoxy)-2,3-dihydropyridine, 1-isopropyl-2-(methylsulfanyl)-3-(1-ethoxyethoxy)pyrrole, and N-isopropyl-N-methyl-3-(1-ethoxyethoxy)-2-thiophenamine prepared from a single linear precursor, adduct of α-lithiated 1-(1-ethoxyethoxy)allene and isopropyl isothiocyanate. All compounds formed a molecular ion (I _rel 1–6%) whose primary fragmentation at the electron impact (70 eV) occurs in two principal directions related to the cleavage of the C-O bonds in the 1-ethoxyethoxy-substituent: with a simple rupture of the bonds C-OEt and C-O(heterocycle) and with the elimination of an ethoxyethene molecule. In the spectra of 4,5-dihydro-3H-azepine and 2,3-dihydropyridine the first fragmentation channel of [M]^+· dominates. The second direction prevailes at the fragmentation of pyrrole and thiophene molecular ions leading to an odd-electrons ion with m/z 171. Further fragmentation of this ion is characteristic of each isomer and resulted in the formation of diagnostic ions providing a possibility of identification of these isomers by mass spectrometry.     

Ammoniakverlust aus α,ω-Alkandiaminen im Massenspektrometer. 22. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen

Loss of ammonia from α,ω-alkanediamines in the mass spectrometer . Under electron impact α,ω-alkanediamines lose ammonia from the molecular ion. This fragmentation reaction is explained in the case of 1.4-butanediamine ( 1 ) on the basis of the spectra of homologues and deuteriated derivatives. The reaction proceeds via neighbouring group participation; the mechanism is given in Scheme 1.     

The influence of vinyl activating groups on β‐allyl sulfone‐based chain transfer agents for tough methacrylate networks

In radical polymerization of monofunctional monomers, addition fragmentation chain transfer (AFCT) agents are well known to regulate polymerization and yield polymers with lower molecular weights and narrower molecular weight distributions. Papers concerning bulk photopolymerization of monomer mixtures with AFCT agents are rarely found in literature. In this article, AFCT reagents based on β‐allyl sulfones with different vinyl activating groups were synthesized and compared. The compounds were tested in mono‐ and difunctional monomer systems providing information about the influence on photoreactivity, molecular weight, as well as thermal and mechanical properties of the resultant polymers. Where more potent activating groups (‐Ph, ‐CN) markedly influenced polymerization at lower concentrations, the AFCT reagent with an ester activating group reacted at a similar rate to the methacrylate monomer (C_T ≈ 1) and provided the best overall performance. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1417‐1427     

Mass spectrometric fragmentation of S-(1-aryltetrazol-5-yl)-monothiocarbonic acid esters

The mass spectra of S-(1-aryltetrazol-5-yl)-monothiocarbonic acid esters have been studied. The stability of the ester molecular ions is lower than the stability of the corresponding 1-aryl-5-mercaptotetrazoles. Substituents at the phenyl group increase the stability, whereas the influence of the ester alkyl groups is very small. The esters undergo fragmentation via four different fragmentation pathways. The elimination of carbon dioxide is influenced by an ‘ortho effect’ of the substituents.     

(+)‐N‐Formylnorglaucine Rotamers from Unonopsis stipitata Diels

(+)‐N‐formylnorglaucine ( 1 ), an aporphine alkaloid containing a formyl group linked to the heterocyclic nitrogen, was isolated from the leaves of Unonopsis stipitata, an Amazon medicinal plant. The chemical structure was characterized based on 1D‐ and 2D‐NMR spectroscopy and HR‐ESI‐MS. NMR spectra revealed that 1 is composed of two rotamers ( 1a and 1b ) in a ratio of approximately 2:1. In addition, the fragmentation behavior of 1 displayed an unusual fragmentation pattern compared to regular aporphine alkaloids. Thus, this compound is reported for the first time as a natural product in this study.     

Macromonomer synthesis using α‐(2‐methyl‐2‐phenylpropyl)acrylates as addition–fragmentation chain‐transfer agents expelling the cumyl radical

α‐(2‐Methyl‐2‐phenylpropyl)acrylate (RS‐2) was examined as a C? C bond‐cleavage type addition–fragmentation chain transfer (AFCT) agent in the benzene solution polymerizations of styrene (St), ethyl methacrylate (EMA), and cyclohexyl acrylate (CHA) with the objective of achieving efficient macromonomer synthesis by radical polymerization. The AFCT efficiency was evaluated in terms of the decrease in the number‐average molecular weight (M_n) upon the addition of the AFCT agent and the number of unsaturated end groups introduced per chain (f). The AFCT efficiency was rationalized by the consideration of the relative importance of AFCT as an end‐forming event and the competition between ‐fragmentation and crosspropagation as adduct radical reaction pathways. In St and EMA polymerizations at 60 °C, RS‐2 resulted in higher f values and lower M_n values than methyl α‐(2‐methyl‐2‐carbomethoxypropyl)acrylate (MMA‐2), and this suggested the facilitation of ‐fragmentation due to the expulsion of the more stable cumyl radical from the RS‐2 adduct radical. Higher f values were observed for MMA‐2 than for RS‐2 in CHA polymerization because of unsaturated end group formation by ‐fragmentation of midchain radicals. However, RS‐2 resulted in lower M_n values for poly(CHA) than MMA‐2 because of a smaller contribution of crosspropagation. Retardation in the presence of the AFCT agents was affected by the balance between b‐fragmentation and crosspropagation and by the addition rate of the propagating radical to the AFCT agent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6021–6030, 2004     

Ortho effects of a nitro group in 2′,3′ and 4′monosubstituted-trans-2,4-dinitrostilbenes on electron impact. IV

The mass spectral fragmentation patterns of thirteen 2′,3′ and 4′-R-trans-2,4-dinitrostilbenes obtained by electron impact have been studied. The main routes of fragmentation involves loss from the molecular ion due to the ortho effects of the 2-nitro substituents. Substitution on positions 2′,3′ and 4′ of stilbene moiety does not influence the fragmentation patterns.     

Mass spectrometry in structural and stereochemical problems—CXCIX Contrasting fragmentations of singly- and doubly-charged o-, m- and p-hydroxyalkylphenones and their trimethylsilyl ethers

High resolution mass spectrometry, metastable defocusing and deuterium labeling of trimethylsilyl (TMS) ethers have been used to study the electron-impact induced fragmentations of o-, m- and p-hydroxyalkylphenones and their TMS ether derivatives. These derivatives have proven useful in contrasting the fragmentation patterns of singly- and doubly-charged ions because of the competing fragmentations: α-cleavage and a McLafferty rearrangement from the ketone moiety and methyl cleavage from the TMS group. A proximity effect was responsible for a markedly increased methyl radical loss from the o-TMS ether. This fragmentation was minor with the m- and p-isomers. Significantly intense doubly-charged ions were formed from ketonic cleavage and by the loss of a TMS methyl radical. The sequence of fragmentation depended on the size of the alkyl group attached to the ketone carbonyl. There was no evidence found for a McLafferty rearrangement occurring from the doubly-charged molecular ion of the TMS ethers of the hydroxyalkylphenones but the rearrangement occurred from the doubly-charge molecular ion of bis-3-(1-oxopentyl)-4-hydroxy-phenyl-methane and, of course, from the singly charged [M]^+. The bis-p-hydroxyphenylmethane derivatives were studied in an effort to increase the intensity of the doubly-charged ions as it was expected that the charges would be separated by a longer distance.