The electron-impact-induced fragmentation of acridine

Studies of both high and low resolution spectra, and of metastable decompositions occurring in both the first and second field-free regions of the mass spectrometer have led to a postulated scheme for the fragmentation of acridine under electron-impact. There is no specific loss of label from either [9-²H₁]acridine or [4,5-²H₂]acridine in any fragmentation, nor is there any total scrambling of label in either molecular ion prior to loss of HCN. There is certainly some degree of scrambling preceding HCN loss from [M]⁺˙ at 70 eV, but this does not involve the 9-H to any detectable extent. There is no strong evidence for the acridine molecular ion having the same structure as that of four other C₁₃H₉N isomers.     

Mass spectral fragmentation pattern of 4,4′-bipyridines. Part II. 4,4′-oxybispyridine and 4,4′-thiobispyridine

The mass spectra of 4,4′-oxybispyridine and 4,4′-thiobispyridine are reported. In the former the base peak is due to the molecular ion and the fragmentation routes involve loss of H, CO, HCN, C₂H₂N and C_sHO from the molecular ion as well as rupture of the central bonds. In the latter the base peak is also due to the molecular ion and the fragmentation routes involve loss of H, CS, S, HCN and C₂HS as well as central bond rupture.     

Mass spectra of some aminonaphthyridines and aminoquinolines

The mass spectra of all the aminoquinolines, the 2–, 3– and 4-amino-1,5-naphthyridines, some amino-1,6-naphthyridines, and two amino-1,8-naphthyridines with methyl substituents are reported. The major fragment in the aminoquinolines is formed by the loss of HCN from the molecular ion. The most abundant fragment in the aminonaphthyridines is formed by the loss of HCN from the molecular ion except in the 2-amino-1,5-naphthyridine isomer. In both 1,8-naphthyridine isomers investigated, the loss of C₂H₂ is an alternate fragmentation pathway of significance. In all of the compounds investigated, the loss of the primary amino group from the molecular ion was found to be an insignificant fragmentation.     

Massenspektrometrische Fragmentieungen Aomatischer Isocyanide

The mass spectra of 19 aromatic isocyanides are reported and discussed. The main feature of the fragmentation of these compounds is loss of HCN usually indicated by a metastable peak. Although this process is characteristic of the behaviour of aromatic isocyanides the extent to which it dominates the mass spectrum of any aromatic isocyanide is determined by the relative ease of cleavage of other bonds within the molecule. 2,4,6-d₃-phenylisocyanide (Ib) loses predominantly DCN from the molecular ion while 2,4-d₂-1-naphthylisocyanide (lIIb) eliminates HCN. It is therefore concluded that the loss of HCN from aromatic isocyanides is mainly a non-random process (no randomization prior to fragmentation).     

Electron-impact induced fragmentation of 2-substituted 2H-cyclopenta[D]pyridazines

The mass spectra of the non-benzenoid aromatic heterocycles 2H- and 2-methyl-2H-cyclopenta[d]pyridazine and several deuterated analogs have been analyzed. The majority of the nitrogen lost from these heterocycles occurs as HCN OR H₂CN. The deuterium labeling suggests a rearrangement of the molecular ion prior to fragmentation.     

Some aspect of the doubly-charged ion chemistry of armoatic amines and diamines

Doubly-charged ion mass spectra of aromatic amines and diamines, as opposed to those of the aromatic hydrocarbons, show strong correlation with empirical formula.[M]⁺⁺is usually the base peak in the spectrum and its main fragmentation involves loss of C₂H₂, in sharp contrast wit the [M]⁺˙ ion which always loses HCN. Measurement of the Kinetic energy released in chargeseparation reactions can yield useful structural information. Result strongly support the concept of charge-localization on nitrogen atoms. Extensive scrambiling prior to nfragmentatiom was observed in all isomeric compoounds studied.     

Mass spectral fragmentation pattern of 2,2′-bipyridyls. Part VIII. 2,2′-Bipyridyl-5-carboxylic Acid and 2,2′-bipyridyl-5-sulphonic acid

The mass spectra of 2,2′-bipyridyl-5-carboxylic acid and 2,2′-bipyridyl-5-sulphonic acid obtained by electron impact are described. The principal initial fragmentation routes from the molecular ion of the carboxylic acid involve loss of CO, CN^˙, HCN, CO₂, OH^˙ and H₂O. From the molecular ion of the sulphonic acid the principal fragmentations are accompanied by loss of HCN, O₃, SO₂ and SO₃.     

Substituent and H/D randomization in the mass spectra of substituted diphenylacetylenic compounds

The mass spectra of several substituted diphenylacetylenes are reported and the [metastable ion]/[daughter ion] ratios for the isomeric chloro- and bromodiphenylacetylenes suggested substituent scrambling in their respective molecular ions. The metastable ion data also indicated equilibration of the chloro substituents in a series of isomeric dichlorodiphenylacetylenes. In addition, the fragmentation patterns for the amino- and nitrodiphenylacetylenes differed somewhat from most other aromatic amino and nitro compounds. The aminodiphenylacetylenes fragment with expulsion of H₂CN from the molecular ion and the expulsion of HCN from the [M – 1]⁺ ion was only a relatively minor reaction. 4-Nitrodiphenylacetylene loses NO from the molecular ion and OH from the [M – NO]⁺˙, whereas the more familiar loss of OH from the molecular ion was not observed. The mass spectra of several deuterated substituted diphenylacetylenes clearly showed extensive (but not complete) H/D equilibration in the molecular ion or some subsequent decomposition ion. Comparative studies between 4-chloro and 4-bromo substituted biphenyl, diphenylacetylene and diphenyldiacetylene indicated similar degrees of H/D randomization, and the results showed that the ? C?C? group did not inhibit the proton equilibration between the two phenyl groups.     

The mass spectrometric fragmentation of n-benzylacetamide

The low energy mass spectra of N-benzylacetamide have been recorded. The major fragmentations of the molecular ion are similar to those observed in the acetanilide spectrum. In addition, the secondary dissociation of the [C₆H₅CH₂NH]⁺ ion by loss of HCN is shown to occur with transfer of the -N–H hydrogen to the ring.     

Positive and negative ion mass spectrometric studies of dioximes of α-diketones and their nickel complexes

The positive and negative ion mass spectra of glyoxime, methylglyoxime, dimethylglyoxime, diphenyl glyoxime and of their nickel(II) complexes are reported. Both the positive and negative ion mass spectra of the dioximes show loss of OH^˙ and H₂O from the molecular ion to give fragment ions which probably have cyclic furazan type structures. The positive ion spectra of the complexes fragment mainly by loss of ligand radicals whereas the negative ion spectra show mainly loss of OH^˙ and H₂O.     

Stereochemical applications of mass spectrometry: 1—The utility of electron impact and chemical ionization mass spectrometry in the differentiation of stereoisomeric benzoin oximes and phenylhydrazones

A study of the electron impact and chemical ionization (H₂, CH₄, and iso-C₄H₁₀) mass spectra of stereoisomeric benzoin oximes and phenylhydrazones indicates that while the former can be distinguished only by their chemical ionization mass spectra the latter are readily distinguishable by both their electron impact and chemical ionization mass spectra. The electron impact mass spectra of the isomeric oximes are practically identical; however, the chemical ionization spectra show that the E isomer forms more stable [MH]⁺ and [MH? H₂O]⁺ ions than the Z isomer for which both the [MH]⁺ and [MH? H₂O]⁺ ions are relatively unstable. In electron impact the Z-phenylhydrazone shows a lower [M]⁺˙ ion abundance and more facile loss of H₂O than does the E isomer. This more facile H₂O loss also is observed for the [MH]⁺ ion of the Z isomer under chemical ionization conditions.     

Mass spectral fragmentation pattern of 2,2′-bipyridyls. Part XII. 2,2′-Selenodipyridine

The mass spectrum of 2,2′-selenodipyridine obtained by electron impact is reported. The base peak in the spectrum is due to the C₅H₄N⁺ ion formed principally by rupture of the central bonds. The molecular ion gives rise to a peak of 50% of the intensity of the base peak. Other fragmentations include loss of H, Se and CSe from the molecular ion and HCN from the M-1 ion.     

Preference factors and isotope effects in the loss of H. (D.) and HCN (DCN) from deuterated pyrazoles upon electron-impact

The mass spectra of deuterated pyrazoles show that loss of H^. and of HCN from the molecular ion occurs with a very high specificity from the 3(5)-position. For the two processes isotope effects and preference factors have been determined. Metastable ion decompositions involving the loss of HCN from the [M - H] -fragment indicate that the identity of the hydrogen atoms in this fragment is lost to a large extent.     

Mass spectra of some N-amino compounds

N-amino compounds on electron-impact commonly lose NH from the molecular ion, and frequently lose N, NH₂ and NH₃. This behaviour contrasts with C-amino compounds which mainly lose HCN and H₂CN. The mass spectra of eight N-amino compounds are recorded and discussed, together with some data from literature sources.     

The fragmentations of substituted cinnamic acids after electron impact

The fragmentations of a number of cinnamic acids substituted at the phenyl ring have been studied with the aid of 70 eV mass spectra and mass analysed ion kinetic energy spectra. Evidence is presented that the formation of [C₉H₇O₂]⁺ ions occurs by intramolecular aromatic substitution reactions. A mechanism is proposed for the energetically favourable loss of the substituents from meta and para positions of the phenyl ring. The analytical use of intramolecular aromatic substitution reactions is briefly discussed.     

Electron-impact induced skeletal re-arrangement of 2-methoxy-3-methylpyrazine and 2-methylthio-3-methylpyrazine

The mass spectra of 2-methoxy-3-methylpyrazine (I), 2-methoxy-6-methylpyrazine (II), 2-methylthio-3-methylpyrazine (III) and 2-methylthio-6-methylpyrazine (IV), are given and the major fragmentation pathways discussed. The novel loss of H₂O from the molecular ion of I and the corresponding loss of H₂S from the molecular ion of III indicate that a skeletal rearrangement takes place in the molecular ion preceding the expulsion of H₂O and H₂S. Proposed mechanisms for this behavior are discussed with evidence being drawn from accurate mass measurement, metastable ions, and deuterium and carbon-13 labeling of the methoxy group. The absence of ions in the spectra of II and IV corresponding to the loss of H₂O and H₂S from these molecular ions clearly indicates that the position of the methyl group with respect to the methoxy group, or the methylthio group is in-timately involved in this mechanism.     

Mass spectrometry of aralkyl compounds with a functional group—IX: Hydrogen scrambling in the molecular ion of hydrocinnamaldehyde

The molecular ion of hydrocinnamaldehyde (C₆H₅CH₂CH₂CHO) chiefly loses fragments C₂H₂O and C₃H₄O. Mass spectra of specifically deuterated analogues show that in the loss of C₂H₂O an α-hydrogen atom (with respect to the aldehyde group) is transferred to the aromatic part. A shift of the aldehydic hydrogen to one of the ortho positions of the phenyl ring and loss of C₂H₂O by a McLafferty rearrangement is not observed. In the loss of C₃H₄O also an α-hydrogen atom migrates to the aromatic part. Both reactions appear to occur with an extensive randomization of all hydrogen atoms in the molecular ion.     

Fragmentation de la Méthyl-2 Indolizine sous Impact Electronique: perte de H˙ à partir de l'Ion Moléculaire; perte de HCN à partir de l'Ion [M?H˙]+

The origin of the hydrogen radical lost in the ionization chamber from the molecular ion of 2-methylindolizine has been studdied by examination of the spectra of four specifically deuterated species. Hydrogen loss involves preferentially a hydrogen from the methyl substituent but also one of the hydrogens of either ring, especially those of the 5-membered ring. The HCN elimination from the metastable [M? H^˙]⁺ ions was studied using a linked scan method; the results are consistent with loss of identity of all the hydrogen atoms of the precursor ion, which implies an extensive reorganization prior to fragmentation.     

Discriminating alkylbenzene isomers with tandem mass spectrometry using a dielectric barrier discharge ionization source

Soft ambient ionization sources generate reactive species that interact with analyte molecules to form intact molecular ions, which allows rapid, sensitive, and direct identification of the molecular mass. We used a dielectric barrier discharge ionization (DBDI) source with nitrogen at atmospheric pressure to detect alkylated aromatic hydrocarbon isomers (C₈H₁₀ or C₉H₁₂). Intact molecular ions [M]^•+ were detected at 2.4 kV_pp, but at increased voltage (3.4 kV_pp), [M + N]⁺ ions were formed, which could be used to differentiate regioisomers by collision-induced dissociation (CID). At 2.4 kV_pp, alkylbenzene isomers with different alkyl-substituents could be identified by additional product ions: ethylbenzene and -toluene formed [M-2H]⁺, isopropylbenzene formed abundant [M-H]⁺, and propylbenzene formed abundant C₇H₇⁺. At an operating voltage of 3.4 kV_pp, fragmentation of [M + N]⁺ by CID led to neutral loss of HCN and CH₃CN, which corresponded to steric hindrance for excited state N-atoms approaching the aromatic ring (C-H). The ratio of HCN to CH₃N loss (interday relative standard deviation [RSD] < 20%) was distinct for ethylbenzene and ethyltoluene isomers. The greater the number of alkyl-substituents (C-CH₃) and the more sterically hindered (meta > para > ortho) the aromatic core, the greater the loss of CH₃CN relative to HCN was.     

Enhanced positive secondary ion emission from substituted polynuclear aromatic hydrocarbon/sulfuric acid solutions

Secondary ion mass spectra of singly substituted aromatic hydrocarbon/H₂SO₄ solutions showed intense aromatic molecular ion and protonated aromatic molecule peaks characteristic of dissolved aromatic compounds from a number of aromatic compound classes, including acids, aldehydes, ketones, nitriles and nitrogen heterocycles. The presence of simultaneously abundant peaks for molecular ions and protonated molecules in secondary ion mass spectra of each aromatic compound/sulfuric acid solution is consistent with known or expected gas-phase proton transfer chemistry. The ratio of intensities, M⁺˙:[M + H]⁺, appears to be determined by sulfuric acid solution chemistry of the compound. Spectra obtained from 1–2 μl samples were relatively free from chemical noise and persisted for up to 20 min. Detection limits for some substituted aromatic compounds are estimated to be 10^?12.