The mass spectra of intramolecularly hydrogen bonded 2(1H)-quinoxalinone and 2H-1,4-benzoxazin-2-one

The mass spectra of those 3-phenacyl derivatives of 2(1H)-quinoxalinone and 2H-1,4-benzoxazin-2-one with an intramolecular hydrogen bonding showd that: (1) the primary elimination of the shole sidchain is reduced as compared with an unchelated derivative; (2) the importan t fragmentation routes in the quinoxalinone series are ring cleavage with loss of CO followed by recyclization and expulsion of a hydrogen atom, and this can also occur in the reverse order; (3) this reverse process is virtually absent in the benzoxazinone series. Finally, the doubly charged molecular ions appear to undergo an analogous decomposition giving fairly intense [M-CO]²⁺ or [M-(CO+H or CI]²⁺ ions.     

Mass spectral study of meso-alkyl and meso-cycloalkyl calix(4)pyrroles under electron impact conditions

A series of meso-cycloalkyl calix(4)pyrroles (I) and meso-dialkyl calix(4)pyrroles (II) has been studied under electron ionization (EI) mass spectral conditions. All the calix(4)pyrroles showed prominent molecular ions. The cleavage of the C--C bond linked at position 2 of the pyrrole ring (beta-cleavage) is the foremost and dominant fragmentation process. The beta-cleavage process, either through ring opening or directly, results in the loss of an alkyl radical from the molecular ion. The collision-induced dissociation (CID) spectra of I showed specific sequential expulsion of pyrrole and/or cycloalkyl rings from the molecular ion with or without hydrogen migrations, revealing more information on the structure of individual compounds than was available from the EI spectra. The isomeric cycloalkyl calix(4)pyrroles showed distinguishable CID spectra, indicating structure specificity in initial ring opening whereas, in the case of II, the EI mass spectrum contains all the structure-indicative fragment ions. The CID spectra of II resulted in a dominant [M-R]+ ion, with other characteristic ions being less abundant.     

Electron impact fragmentation of 2-arylhydrazonopropandioic acid derivatives

Examination of the mass spectra of eleven 2-arylhydrazonopropandioic acid derivatives reveals that a radical ion which is tentatively formulated as a 1H-diazirine species is produced in each case (except for the diphenyl este) by more than one process. Formation of what is formally the aryl amine radical ion occurs by a novel hydrogen rearrangement. Simple cleavage of the bonds β to either the aromatic ring or the C?N moiety also produces abundant ions. The diphenyl ester behaves anomalously yielding the phenol ion instead of the amine. The proposed mechanisms were confirmed by metastable studies, deuterium labelling and exact mass measurements.     

Mass spectrometry of heterocyclic compounds. V—Substituent effects on the fragmentation pathways of 3,5-diphenyl-1,2,4-oxadiazole derivatives

The 70 eV mass spectra of a number of derivatives of 3,5-diphenul-1,2,4-oxadiazole substituted either in the 5-phenyl (fifteen) or in the 3-phenyl (four) position, have been studied using exact mass measurements and metastable determinations by the defocusing technique. The substituent effects on the heterocyclic cleavage are not very important for electron-withdrawing and weak electron-donating groups. The main cleavage is the formal retro 1,3-dipolar cycloaddition with the positive charge retained by the C₇H₅NO (orYC₇H₄NO in the case of the 3-substituted derivatives) fragment specifically containing the 3-phenyl, as oreviously observed for 3,5-diphenyl-1,2,4-oxadiazole using labelling experiments. Two other minor primary processes leading to benzoyl and nitrile ions, both containing the 5-phenyl, become important in the case of the electron-donating substituted compounds. Correlation of the abundance of these fragmednts and of the molecular ions with σ⁺ (para) Brown constants is discussed. Proximity effets are shown by some ortho derivatives.     

Mass spectra of some 4,5-dihydroimidazole derivatives

The mass spectra of a series of 4,5-dihydroimidazole derivatives were determined. Deuterium labelling and high resolution mass spectrometry were utilized in order to elucidate the mechanism of a number of fragmentations. The most significant ions arise from the following processes: (1) elimination of the C-4 substituent; (2) cleavage of the 1,2-N? C and 4,5-C? C bonds with or without hydrogen migration; (3) cleavage of the 1,5-N? C and 2,3-C? N bonds with charge retention on the N-1? C-2 moiety.

1 In this paper the standard numbering of the imidazole ring (see structures) is retained for the fragment ions.

Anomalous behaviour is shown by the t-butoxy derivative; the reasons for this behaviour are discussed.     

Fragmentation of some even-electron nitroaromatic ions: The question of the nitrotropylium ion

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.     

Mass spectrometry of substituted 1,3-dihydro-2H-imidazole-2-thiones

The electron impact mass spectra of the 4-formyl-1, 3-dihydro-2H-imidazole-2-thione, its six 1-methyl(n-propyl, n-hexyl)-3-methyl(phenyl)-disubstptuted derivatives, and the 1,3-dihydro-1-phenyl-2H-imidazole-2-thiome are discussed. The fragmentation pattern is strongly influenced by the alkyl or phenyl N-substituents, as well as by the length of the alkyl chain. The odd-electron ions containing an N-phenyl substituent, but not a propyl or hexyl group, eject a hydrogen atom from the phenyl ring, while the presence of a long alkyl chain greatly enhances the loss of the sulphyhydryl radical and facilitates the expulsion of several alkenes, and alkyl and alkenyl radicals.     

Fragmentation pathways of oxygenated tetracyclic triterpenoids and their application in the qualitative analysis of Ganoderma lucidum by multistage tandem mass spectrometry

The fragmentation pathways of oxygenated tetracyclic triterpenoids from Ganoderma lucidum were systematically studied based on interpreting the mass spectra of 44 known triterpenoids using a combination of multistage tandem mass spectrometry (MS(n)) experiments and high-resolution mass spectrometry (HRMS) analysis. In negative ion mode, the fragmentation pathways of triterpenoid acids are rather characteristic. After the prominent loss of H(2) O or CO(2), cleavages take place on the A, B, C and D rings. Interestingly, the cleavage mode is highly dependent on the positions of the carbonyl groups and hydroxyl groups in the tetracyclic skeleton. Characteristic cleavage of ring A occurs in 7-oxo-11-H or 7-oxo-11-hydroxy derivatives; characteristic cleavage of ring B occurs in the 7-oxo-11-hydroxy derivatives; characteristic cleavage of ring C occurs in the 7-hydroxy-15-oxo derivatives; while the cleavage of ring D can be observed in the majority of the compounds investigated. The odd-electron species, which disobey the 'even-electron rule', are also observed and discussed in this paper. These phenomena provide an easy way to determine the tetracyclic skeleton and distinguish the isomers of the triterpenoids from each other. What is more, the fragmentation pathways of triterpenoid alcohols were also investigated in positive ion mode. The accurate masses of the product ions were determined using quadrupole orthogonal time-of-flight (QTOF) instruments. Finally, the fragmentation rules were applied to identify the components of G. lucidum. As a result, 73 triterpenoids including 11 new ones were identified. The triterpenoids were classified into six subclasses according to their different fragmentation behaviors. The application of tandem mass spectrometry was further explored.     

Tetracyclic phenothiazines. VII. Electron impact promoted mass spectral fragmentation of some pyrido[3,2,1-kl]phenothiazines

The mass spectral fragmentation pattern of a series of pyrido[3,2,1-kl]phenothiazines is reported. The major fragments are derived from the breakdown of the pyrido ring and substituents thereon. The 1,2-/2,3-unsaturated, unsubstituted and most of the 3-substituted compounds show the molecular ion as the base peak indicative of their relative stability toward electron impact. The genesis of the base peaks from the molecular ions of the 2,2-dithiophenyl substituted compounds probably involves a concerted expulsion of a neutral diphenyldisulfide molecule and hydrogen atom transfer from the 1-position to the 2-position in the pyrido ring. On the other hand, 2-thiophenyl substituted molecular ions lead to base peaks involving simultaneous ring opening of the pyrido ring, cleavage of phenylthiomethylene moiety as a radical and contractive ring closure to the pyrrole system. These two mechanisms appear to be diagnostic for distinguishing 2,3- versus 2,2-positional isomers. The McLafferty rearrangement takes place in the 2-thiophenyl and 2,2-dithiophenyl substituted compounds. The retro-Diels-Alder fragmentation of the pyrido ring occurs in varying degrees depending on the nature of the 2- and 3- substituents and also the presence or absence of unsaturation in the pyrido ring. In the 2-thiophenyl-3-keto compounds, thiophenyl group participation with 3-carbonyl carbon and oxygen atoms is observed in the genesis of some interesting ion fragments. The detection of metastable ions in the spectra of 1,2-dihydro-2-thiophenyl-, 1,2-dihydro-2,2-dithiophenyl-3-hydroxy-, and 1,2-dihydro-2,2-dithiophenyl-3-keto-3H-pyrido[3,2,1-kl]phenothiazines; and spectra of 1,2-dihydro-3-methyl-, 1,2-dihydro-2-carbethoxy-3-keto- and 1,2-dihydro-2-thiophenyl-3-keto-3H-pyrido[3,2,1-kl]pheno-thiazines at low voltage support major fragmentation pathways.     

罗丹明-三嗪衍生物的合成及探针性质

在控制反应温度的条件下, 用罗丹明B酰肼(或罗丹明B乙二胺)选择性分步取代三聚氯氰环上的活性氯, 合成了系列罗丹明-三嗪衍生物. 考察了不同取代获得的衍生物的探针识别性能, 发现所制备的衍生物能高灵敏、高选择性地识别Al³⁺, Cr³⁺或Cu²⁺离子, 是一类性能良好的金属离子荧光和比色增强型探针.     

The ion kinetic energy spectra of isomeric chlorobenzenes and polychlorinated biphenyls (PCB'S)

The ion kinetic energy (IKE) spectra of the isomeric di-and trichlorobenzenes have been examined and the data for the latter compounds suggested that there was incomplete chlorine randomization in their molecular ions in the first field-free region of the mass spectrometer. Previous studies on the mass spectra and [metastable ion]/[daughter ion] ratios of the di-, tetra- and hexachlorobiphenyls (PCB's) indicated chlorine randomization in the molecular ions of those isomers containing less than two chlorine groups ortho to the Ph-Ph ring junction. In contrast the IKE spectra of the isomers are different and the results indicate incomplete chlorine randomization in the first field-free region of the mass spectrometer. These spectral differences may be of some use in PCB analysis.     

Zur lokalisierung funktioneller gruppen in steroiden mit hilfe der massenspektrometrie—VII : 3,11-Dihydroxypregnan-20-one

The mass spectrometric degradation reactions of 3,11-dihydroxypregnan-20-ones concern mainly cleavage reactions in the D ring. Characteristic fragments are the ions of mass 43 combined with ions of mass 84 and 85. Equally, after single and double loss of water CH₃CO? is eliminated, as well as C 15–17, C20 and C21.All spectra of 3,11-dihydroxypregnan-20-ones are characterised by a key fragment of mass 190 produced by cleavage of bonds in the B ring.Ions with an 11α-OH group show important ions of mass 124 which are dominating if the A/B ring system is cis connected. In contrast the configuration of an OH group in position 3 can hardly be deduced by the spectra.     

Electron ionization mass spectral fragmentation of derivatized 4,5- and 5,6-epoxysterols

The electron ionization (EI) mass spectral fragmentation of derivatized 4,5- and 5,6-epoxysterols was investigated. Interesting fragmentation processes involving a transannular cleavage of the epoxide ring after transfer of the trimethylsilyl group are significant in the case of 4,5-epoxysterol trimethylsilyl ethers (affording abundant fragment ions at m/z 403 and 404). Different pathways, which have been substantiated by deuterium labelling, are proposed in order to explain the formation of these ions. In contrast, this transfer is not significant in the case of 5,6-epoxysterol trimethylsilyl ethers. The EI mass spectra of these latter compounds appear to be very complex and to differ slightly according to the stereochemistry of the epoxy group. Acetate and trifluoroacetate derivatives of 4,5-epoxysterols display interesting EI mass spectra dominated by a fragment ion at m/z 332 resulting from cleavage of the steroid ring A.     

Characterization of iridoids by fast atom bombardment mass spectrometry followed by collision-induced dissociation of

Fast atom bombardment mass spectra of a series of naturally occurring and synthetically modified iridoid glycosides were studied using lithium cationization and collision-induced dissociation of the resulting [M+Li]+ ions. Lithium cationization leads to the unambiguous determination of the molecular masses of these compounds. Collision-induced dissociation of the lithiated molecular ions give valuable structural information regarding the nature of the substituent on both the aglycone and the sugar moieties. The characteristic fragmentation pathways identified are (1) elimination of neutral molecules comprising the substituents on either the aglycone or sugar moieties, (2) formation of lithiated aglycone and their fragment ions, (3) formation of lithiated sugar and their fragment ions, (4) fragmentation corresponding to the cleavage of the aglycone or sugar ring and (5) fragmentation characteristic of the substituents present in either the aglycone or sugar parts of the molecule. Elimination of two acyloxy radicals from the lithiated molecular ion is a characteristic fragmentation in the case of acyloxy derivatives.     

Vergleich der Produkte aus der Reaktion von Phenylguanidin-Derivaten mit β-Ketoestern bzw. Propiolsäureestern (Synthese von Pyrimidonen)

Comparison of reaction products afforded by phenylguanidine derivatives with β-ketoesters or propiolic esters, respectively (synthesis of pyrimidones). 2-Anilino-imidazolines, when treated with either β-ketoesters or propiolic esters, yield two isomeric groups of pyrimidones. The isomerism is based on different positions of the carbonyl group in the pyrimidone ring. The mass spectra permit an unequivocal assignment of constitution I to the product formed with β-ketoesters and of constitution V to that formed with propiolic esters. Additionally, 2-(2-amino-anilino)-2-imidazoline (XII) when treated with methyl phenylpropiolate yields IX; while treatment with ethyl benzoylacetate yields XIII as an intermediate, which eliminates spontaneously one molecule of water to give the benzimidazole derivative XIV. Phenylguanidines (XV) add propiolic esters in the same way as do imidazoline derivatives. Photochemical cleavage of two carbon atoms with their adherent hydrogen atoms from the imidazole ring of the pyrimidones (V) leads to aminopyrimidine derivatives, e.g. XVI.     

Mass spectra of 1,2,4-triazoles—II: Alkyl 1,2,4-triazoles

The mass spectra of monomethyl 1,2,4-triazoles contain fragment ions produced by specific cleavage of the heterocyclic ring. A major fragmentation from many molecular ions involves the elimination of HCN, but loss of N₂ is either very small or completely absent. No N or H scrambling occurs within the triazole ring system, as evidenced by labelling studies. The loss of a hydrogen atom from the molecular ions of 3-alkyl-1,2,4-triazoles (alkyl ? C₂H₅) originates from hydrogens attached to the β carbon and nitrogen atoms.     

Mass spectra of o-aminobenzophenones

The electron impact induced fragmentation of chlorine substituted o-aminobenzophenones has been examined. All the compounds show ions formed by α-cleavage on either side of the carbonyl group. The relative intensity of the resulting ions is predictable from the quasi-equilibrium theory. The most important features of the mass spectra of these compounds are, however, intense [M? H]⁺ ions for the primary amines and [M – OH]⁺ ions for the N-methylated compounds. These and other less intense peaks as well as some metastable ions allows structural elucidation.     

Mass spectra of azetidines and 2-azetidinones

The mass spectra of twenty three azetidines and seventeen 2-azetidinones are reported and discussed. The majority of spectra contain molecular ions. Fragmentation modes are largely dependent upon the substitution pattern and involve specific cleavage of the four-membered ring. Several hydrogen rearrangement reactions occur, and in some cases, cis and trans isomers may be distinguished by large differences in the relative abundances of certain fragment ions.     

Fragmentation Study of Limonoids from Turraae pubescens by Electrospray Ionization Quadrupole Time-of-flight Mass Spectrometry

Nine representative limonoids isolated from Turraae pubescens were investigated by electrospray ionization quadrupole time-of-flight tandem mass spectrometry in positive ion mode. Although the structures of these compounds are similar, the corresponding fragmentation patterns and mass spectrometry and tandem mass spectrometry (MS/MS) spectra are clearly different. For Turrapubin A–C, product ions can be detected in both low and high mass ranges. A McLafferty-type rearrangement is the only way for the cleavage of C9–C10. For 11-epi-toonacilin, Turrapubin E, Turraflorin A, 11-epi-23-hydroxytoonacilide, Turrapubin H and 11-epi-21-hydroxytoonacilide, the cleavage of C9–C10 goes through two different ways, including McLafferty-type rearrangement and homolytic cleavage. The relative abundances of product ions from McLafferty-type rearrangement for 11-epi-toonacilin, 11-epi-23-hydroxytoonacilide, and Turrapubin H are high, while those for Turrapubin E, Turraflorin A, and 11-epi-21-hydroxytoonacilide are low. A pair of epimers was distinguished unambiguously by MS/MS spectra. It was found that the substituent group at C-1, hydroxy group, O atom linked to C-14 and C-15, and the oxygenated furan ring were the important factors leading to the differences of their MS/MS spectra.     

Collisional-activated decomposition of benzyloxycarbonyl-protected tripeptide derivatives containing proline in fast atom bombardment mass spectrometry

The effect on the fragmentations of N-benzyloxycarbonyl-protected tripeptide ethyl esters due to the existence of L -proline in the gas phase was examined by the collisional-activated decomposition of the deprotonated molecule and the fragment ions produced by the cleavage of the tripeptide derivatives containing the neutral amino acids (L -alanine, L -leucine and L -phenylalanine) and L -proline, in which changes in both the numbers and positions of the prolyl residues were observed, in negative-ion fast atom bombardment mass spectrometry. The cleavage patterns of these ions in the collisional-activated decomposition mass spectra were observed to depend on the numbers and positions of prolyl residues in the peptide derivatives. These results indicate that the conformational differences in the peptide derivatives due to the existence of L -proline affect the decomposition of the ions containing the neutral amino acids in the gas phase.