Mass spectrometric study of 4-azafluorenes

The dissociative ionization of 4-azafluorene and its methyl and phenyl derivatives was investigated. The relative intensity of the [M — CH₃]⁺ ion peak depends on the position of the CH₃ group in the 4-azafluorene ring. It was established that the loss of an RCN particle (R=H, CH₃, and C₆H₅) for unsubstituted 4-azafluorene takes place from the M⁺ and [M — H]⁺ ion, exclusively from the [M — H]⁺ ion for the methyl-substituted compounds, and from the [M — H]⁺ and [H — 2H]⁺ fragments for the phenyl-substituted derivatives. Randomization of the deuterium ions in the 9,9-d₂-4-azafluorene molecular ion was observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 246–250, February, 1978.     

Fragmentation of 2- and 4-(2-furyl) pyridines under the influence of electron impact

The dissociative ionization of 12 compounds of the 2- and 4-(2-furyl)pyridine series that contain methyl, ethyl, and n-propyl groups in various positions of the pyridine ring was investigated. It was established that the intensity of the [M — H]⁺ ion peak depends only slightly on the mutual orientation of the alkyl groups and the furyl grouping, while the probability of cleavage of the furan ring with ejection of CO and HCO particles is very sensitive to these structural factors. Cleavage of the pyridine ring leads to the development of [M — HCN]⁺ and [FuCN]⁺ ions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 769–774, June, 1982.     

Mass spectrometric study of methyl-substituted 4-azaphenanthrenes and their nitration products

The mass spectral behavior of five derivatives of the 4-azaphenanthrene series — 1,3-dimethyl-(I), 2,3-dimethyl-(II), 1,2,3,-trimethyl-(III), 1,2,3-trimethyl-8-nitro-(IV), and 1,3-dimethyl-6,7-dinitro-4-azaphenanthrene (V) — was studied. The stabilities of the molecular ions with respect to gragmentation (W_M) are higher by a factor of two or more for the methyl-substituted I–III than for nitro derivatives IV and V. The intensity of the [M-H]⁺ ion peak in the mass spectra of I–V does not depend on the number of methyl groups but only on their positions: the presence of a CH₃ group in the 2 position leads to an [M-H]⁺ ion that is 1.5 times more intense than when there is a methyl group in the 1 position. The molecular ions of I–V do not eliminate HCN molecules; this constitutes evidence for the absence of randomization of their methyl groups. The presence of a CH₃ substituent in the 1 or 2 position does not affect the intensity of the [M-CH₃]⁺ ion peaks, while the simultaneous presence of CH₃ groups attached to the C₁ and C₂ atoms increases the intensity of the [M-CH₃]⁺ fragment peak by a factor of two. In the mass spectra of nitro derivatives IV and V, [M-O]⁺, [M-OH]⁺, [M-NO]⁺, and [M-NO₂]⁺ fragments are observed in the first step of the fragmentation of the M⁺ ion, whereas the [M-CO]⁺ ion peak characteristic for the dissociative ionization of 1-nitronaphthalene is also observed for 8-nitro-substituted IV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1365–1369, October, 1977.     

Mass-spectrometric behavior of isomeric nitro- and nitroaminoindolizines and indoles

Peaks of [M — NO]⁺ and [M — NO₂]⁺ ions are characteristic for the mass spectra of nitroindolizines, whereas peaks of ions of the indole type, viz., [M — HCN]⁺ and [M- H,- HCN]⁺ (for alkylindoles), are not characteristic. In the mass spectra of nitroindoles the latter ions give more intense peaks, while the loss of a nitro group or its rearrangement is a considerably less significant process. When a dialkylamino group is introduced in the nitroindolizine molecule, the primary processes in the fragmentation of such compounds are due to fragmentation of the alkylamino group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 765–768, June, 1982.     

Mass-spectrometric study of nitro derivatives of 2(4)-azafluorenes and 2(4)-azafluorenones

The dissociative ionization of 13 nitro derivatives of 2(4)-azafluorenes and 2(4)-azafluorenones was investigated. The introduction of an electron-acceptor nitro group into the molecule markedly reduces the stability of the molecular ions and suppresses the fragmentation pathways that are characteristic for azafluorenes. Nitro-nitrite rearrangement proceeds more readily in nitro-substituted 4-azafluorenes than in nitro-substituted 2-azafluorenes. A characteristic feature of the fragmentation of azafluorenes that do not contain nitro and methyl groups in a vicinal orientation is elimination of a OH particle by the molecular ions. It was established by deuterium labeling that in this case the formation of an [M — OH]⁺ ion is due to the presence of a methylene group attached to the C₉ atom in the molecule.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 941–947, July, 1981.     

Mass spectra of chlorinated esters: 2—Methyl mono- and dichlorobutanoates

The mass spectral fragmentations of methyl mono- and dichlorobutanates have been studied. Deutrium labelling and metastable ion analysis were used to elucidate the fragmentation mechanisms. The molecular ion peaks of the esters are weak and show only in the spectra of the monochloro isomers. A McLafferty rearrangement gives the base peaks in the spectra of methyl 2-chloro-, 4-chloro- and 4,4-dichlorobutanoate; α-cleavage, [COOCH₃]⁺, in methyl 2,2- and 2,4-dichlorobutanoate; [M? Cl]⁺, in methyl 3-chlorobutanoate; [M? Cl? HCl]⁺, in methyl 3,4-dichlorobutanoate; [M? Cl? CH₂CO]⁺, in methyl 3,3-dichlorobutanoate and [M? Cl? COOCH₃]^+˙, in methyl erythro- and threo-2,3-dichlorobutanoate. The mass spectra of the stereoisomers are nearly identical, the loss of a chlorine atom and the McLafferty rearrangement giving the higher peaks in the spectrum of the threo form.     

Mass spectrometry of stereoisomeric 3-hydroxy-4-piperidones

The existence of several sites of charge localization upon the mass spectrometric decomposition of stereoisomeric 3-hydroxy-4-piperidones leads to a large number of fragmentation products both with retention and destruction of the piperidine ring. Analysis of the mass spectra of the compounds studied showed that the appearance of [M — CO]⁺ ion peaks for isomers with an axial hydroxyl group may serve as a method for determining the configuration of the carbinol site of such cyclic structures.Translated from Khimiya Geterotsiklichesikh Soedinenii, No. 3, pp. 375–379, March, 1986.     

Electron impact mass spectra of chlorinated methyl propanoates

The mass spectral fragmentations of all eleven chlorinated methyl propanoates have been studied. Deuterium labelling and metastable ion analysis were used to elucidate the fragmentation mechanism. The molecular ion peaks of all compounds are small, except methyl 3,3-dichloropanoate (38%). In most cases α-cleavage gives the base peak [COOCH₃]⁺, and the loss of a chlorine atom from the molecular ion is characteristic of the 3-chloro, 3,3-dichloro and 3,3,3-trichloro compounds. Metastable ions showed the losses of small neutral molecules such as CH₃OH, CH₂CO, CO₂ and CO from the [M? Cl]⁺ ion. α-Cleavage and the loss of Cl^˙ gives an intense [M? COOCH₃? Cl]^+˙ peak, which is the base peak in the spectra of the 2,3-dichloro and 2,3,3-trichloro compounds.     

Rearrangement of molecular ions following electron impact: IV—Origin of the [M—28]+˙ ions in the mass spectra of α-methyl-2-decalone

The transposition of the molecular ions (ring contraction) of 2-decalones is demonstrated by a study of the [M–28]⁺˙ peak and its homologue in labelled products using ionization and appearance energy measurements, and mass analysed ion kinetic energy and collision induced dissociation spectra.     

Mass spectral study of ring E of taraxasterol and compounds with similar ring substitution

The origin of the [M–69]⁺ and [M–111]⁺ signals in the mass spectrum of taraxasterol was studied through the use of C(18), (19), (21), (22) and/or (30) deuteriated derivatives. The generality of these signals for ring systems with an exocyclic methylene group and a methyl moiety on an adjacent carbon was verified with 2-methylmethylenecyclohexane, 1-methyl-2-methylene-trans-decalin, 1,10-dimethyl-2-methylene-trans-decalin and some of their deuteriated derivatives. The most plausible mechanism for the formation of the [M–69]⁺ ion appears to involve cleavage of both bonds allylic to the exocyclic methylene group with a 1,3-hydrogen transfer from the adjacent ring. Genesis of the [M–111]⁺ ion is more complicated but a five-membered allylic ion generated from ring D is proposed.     

Differences in the mass spectra of isomeric benzolactams

It is shown that 3- and 4-substituted dihydro-2-quinolones can be distinguished from the isomeric dihydro-1-isoquinolones by mass spectrometry. The [M - CO]⁺ ion is characteristic for the mass spectra of dihydroquinolone derivatives, whereas retrodiene fragmentation of the molecular ion is characteristic for dihydroisoquinolone derivatives. The intense [M - R]⁺ and [M - R, - H₂O]⁺ ion constitute evidence that the substituent is located in the 3 (for dihydroisoquinolones) or 4 (for dihydroquinolones) position. The processes that occur in the fragmentation were confirmed by data from the high-resolution mass spectra, an analysis of the observed metastable ions, and an analysis of the mass spectra of 3-methyl-3,4-dihydro-1-isoquinolone and 4-methyl-3,4-dihydro-2-quinolone containing deuterium attached to the nitrogen atoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 246–249, February, 1979.     

Mass-spectrometric study of physiologically active β-thiosemicarbazones of N-alkylisatins

The molecular ions of isatin (I) and N-methyl- (II) and N-ethylisatin (III) -thiosemicarbazones undergo fragmentation via many pathways with the elimination of NH₃, H₂S, CO, CH₂N₂, CHN₃, CH₂N₂S, CH₂NS, and CHNS particles; this is due to primary localization of the charge on the heteroatoms of the thiosemicarbazone residue. A previously unknown rearrangement, which consists in migration of an HS group to the -carhon atom of the heteroring with subsequent ejection of a CHN₃ fragment. The [M — CO]⁺ ions undergo fragmentation with the elimination of CH₂N₂S; in the case of II and III fragmentation is preceded by detachment of a hydrogen atom (II) or a methyl group (III) from the substituent attached to the ring nitrogen atom. The [M — CO, -H, -CH₂NS]⁺ (II) and [M — CO, -CH₃, -CH₂N₂S]⁺ (III) ions undergo fragmentation with the ejection of HCN in two ways through both the ring nitrogen atom and the thiosemicarbazone residue. Schemes for the principal pathways of fragmentation and rearrangements are presented. The compositions of the ions were confirmed by the high-resolution mass spectra and the mass spectra of the N-deuteroalkyl derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 75–79, January, 1979.     

Electron ionization-induced loss of a methyl radical from 1-cyclopropyl-4-substituted-1,2,3,6 tetrahydropyridine derivatives

The electron ionization mass spectra of 1-cyclopropyl-4-substituted-1,2,3,6-tetrahydropyridine derivatives are characterized by a base peak corresponding to [M-15]⁺. Evidence is presented to support a fragmentation process involving an initial cyclopropyl ring opening of the parent cyclopropylaminyl radical cation followed by intramolecular transfer of a hydrogen atom from the ring carbon atoms α to nitrogen to the primary carbon-centered radical and finally a fragmentation step proceeding by loss of a methyl radical and formation of a stable N-ethenyldihydropyridinium ion, the [M-15]⁺ fragment.     

A mass spectral study of 1-(aryldimethylsilyl)-2-propanones and their isomeric 2-(aryldimethylsiloxy)-1-propenes

The mass spectra of a series of β-ketosilanes, p-Y? C₆H₄Me₂SiCH₂C(O)Me and their isomeric silyl enol ethers, p-Y? C₆H₄Me₂SiOC(CH₃)?CH₂, where Y = H, Me, MeO, Cl, F and CF₃, have been recorded. The fragmentation patterns for the β-ketosilanes are very similar to those of their silyl enol ether counterparts. The seven major primary fragment ions are [M? Me·]⁺, [M? C₆H₄Y·]⁺, [M? Me₂SiO]⁺˙, [M? C₃H₄]⁺˙, [M? HC?CCF₃]⁺˙, [Me₂SiOH]⁺˙ and [C₃H₆O]⁺˙ Apparently, upon electron bombardment the β-ketosilanes must undergo rearrangement to an ion structure very similar to that of the ionized silyl enol ethers followed by unimolecular ion decompositions. Substitutions on the benzene ring show a significant effect on the formation of the ions [M? Me₂SiO]⁺˙ and [Me₂SiOH]⁺˙, electron donating groups favoring the former and electron withdrawing groups favoring the latter. The mass spectral fragmentation pathways were identified by observing metastable peaks, metastable ion mass spectra and ion kinetic energy spectra.     

Mass spectrometry of aryl substituted di- and trisiloxanes

The mass spectra of arylpentamethyldisiloxanes, sym-diaryltetramethyldisiloxanes and 1,5-diaryl-1,1,3,3,5,5-hexamethyltrisiloxanes were examined. Isotopic labeling and peak matching were used to substantiate the proposed fragmentation mechanisms. Siliconium ions dominate the spectra. Loss of neutral fragments from the [M-15]⁺ ions is important. Phenylpentamethyldisiloxane, sym-tetramethyldiphenyldisiloxane and 1,1,3,3,5,5-hexamethyl-1,5-diphenyltrisiloxane are representative examples of the three classes of compounds discussed. The [M-15]⁺ ion of phenylpentamethyldisiloxane loses methane, dimethylsilanone [(CH₃)₂Si?O] and phenylmethylsilanone [PhCH₃Si?O] to yield daughter siliconium ions. The [M-15]⁺ ion of sym-tetramethyldiphenyldisiloxane loses benzene, methane, dimethylsilanone and phenylmethylsilanone to yield daughter siliconium ions. The [M-15]⁺ ion of 1,1,3,3,5,5-hexamethyl-1,5-diphenyltrisiloxane loses benzene, tetramethylcyclodisiloxane and phenyltrimethylcyclodisiloxane to yield daughter siliconium ions. Finally, doubly charged ions are important in the mass spectra of the three series of aryl substituted di- and trisiloxanes discussed.     

Über quantitative Beziehungen Zwischen Fragmenten und Ihren Relativen Intensitäten im Massenspektrometer. III—Messung der Intensitätsverhältnisse aus der α-SWpaltung von Tertiären Alkjoholen und Äthern bei Niedriger Elektronenenergie

The ion intensity ratios from competing α-fissions of 30 tertiary aliphatic alcohols and 24 ethers of tertiary alcohols have been measured at 13 eV. The intensity ratios of ions [M ? alkyl1]+ and [M ? alkyl2]⁺ agree well with the reciprocal mass ratios of the respective ions in the case when the alkyl groups are not methyl (ion mass effect). The intensity ratios of [M ? alkyl]⁺ and [M ? methyl]⁺ are always too high, but intensity ratios of [M ? alkyl1]⁺ and [M ? alkyl2]⁺ may be derived indirectly from them, which also agree well with those values expected from the ion mass effect. By the indirect method it is shown, that for the 2,2-dialkyl-1,3-dioxolanes (ethylene ketals) the ion mass effect plays a dominant role too.     

Mass spectrometry of stable free radicals—II: pyrrolidine nitroxides

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.     

Evaluation of the α‐phenylvinyl cation as a chemical ionization reagent for the differentiation of isomeric substituted phenols in an ITMS

Ion–molecule reactions between the α‐phenylvinyl cation and isomeric naturally occurring phenols were investigated using a quadruple ion trap mass spectrometer. The α‐phenylvinyl cation m/z 103, generated by chemical ionization from phenylacetylene, reacts with neutral aromatic compounds to form the characteristic species: [M + 103]⁺ adduct ions and the trans‐vinylating product ions [M + 25]⁺, which correspond to [M + 103]⁺ adduct after the loss of benzene. Isomeric differentiation of several ring‐substituted phenols was achieved by using collision‐induced dissociation of the [M + 103]⁺ adduct ions. This method also showed to be effective in the differentiation of 4‐ethylguaiacol from one of its structural isomers that displays identical EI and EI/MS/MS spectra. The effects of gas‐phase alkylation with phenylvinyl cation on the dissociation behavior were examined using mass spectrometryⁿ and labeled derivatives. Copyright © 2015 John Wiley & Sons, Ltd.     

The mass spectra of alkylbenzenes—II. The formation of [M ? methyl]+ from tri- and tetra-methylbenzenes

A study of the [M ? methyl]⁺ ion in the mass spectra of ring-deuterated tri- and tetramethylbenzenes has confirmed the partial randomisation of hydrogen and deuterium atoms observed by other workers. The results can be explained by postulating randomisation of the peripheral entities, followed by several cycles of ring expansion and contraction, prior to fragmentation.     

A fast atom bombardment and field ionization/field desorption study of some isomeric unsaturated dicarboxylic acids

Geometrically isomeric dicarboxylic acids, such as maleic and fumaric acid and their methyl homologues, and the isomeric phthalic acids, have been investigated using fast atom bombardment, field ionization and field desorption mass spectrometry. The most intense peak in the positive ion fast atom bombardment spectra corresponds with the [M + H]⁺ ion. This ion, when derived from the E -acids, tragments either by successive loss of water and carbon monoxide or by elimination of carbon dioxide. In the case of the Z -acids only elimination of water from the [M + H]⁺ ions is observed to occur to a significant extent. The same is true for the [M + H]⁺ ions of the isomeric phthalic acids, that is the [M + H] ions derived from iso- and terephthalic acid exhibit more fragmentation than those of phthalic acid. All these acids undergo much less fragmentation upon field ionization, where not only abundant [M + H]⁺ ions, but also abundant [M]^+· ions, are observed. Upon field desorption only the [M + H]⁺ and [M + Na]⁺ ions are observed under the measuring conditions. Negative ion fast atom bombardment spectra of the acids mentioned have also been recorded. In addition to the most abundant [M? H]^? ions relatively intense peaks are observed, which correspond with the [M]^?˙ ions. The fragmentations observed for these ions appear to be quite different from those reported in an earlier electron impact study and in a recent atmospheric pressure ionization investigation.