Mass spectra of indazolones and pyrazolones—II: 5-pyrazolones

The mass spectral fragmentations of 3-methyl-5-pyrazolone (I), 3-methyl-5-pyrazolone-1-d₁ (II), 3-methyl-5-pyrazolone-1,4,4-d₃ (III), 1-acetyl-3-methyl-5-pyrazolone (IV), 3-methyl-5-ethoxy-pyrazole (V), 3,4-dimethyl-5-pyrazolone (VI), 1,3-dimethyl-5-pyrazolone (VII), 1-acetyl-5-acetoxy-3,4-dimethylpyrazole (VIII), 1,2,3-trimethyl-5-pyrazolone (IX), 3,4,4-trimethyl-5-pyrazolone (X), 3,4,4-trimethyl-5-pyrazolone-1-d₁ (XI), 3-phenyl-5-pyrazolone (XII), 2-acetyl-3-phenyl-5-pyrazolone (XIII) and 5-acetoxy-3-phenylpyrazole (XIV) are reported. Comparison is made between the mass spectra of 5-pyrazolones and 3-indazolones. As for the latter compounds initial loss of ·N₂R is preferred to loss of ·CHO, and is followed by loss of CO. The [M ? 1]ions are intense in the C-methyl substituted pyrazolones, and unlike the 3-indazolones, the pyrazolones do not show any significant loss of HCN from these ions. The mass spectra distinguish between certain isomeric 5-pyrazolones.     

Hydrogen randomization in phenyl azide

The loss of both HCN and C₂H₂ from the phenyl nitrenium cation radical generated from 2,4,6-d₃-phenyl azide is preceded by H/D randomization.     

The question of hydrogen and randomization in phenyl isocyanide

The loss of HCN and DCN from 2,4,6-d₃-phenyl isocyanide is preceded by H/D randomization in the large majority of k-states which could be sampled in this study.     

Mass spectra of some syn- and anti-aromatic aldoximes

The mass spectra of eight pairs of geometric isomers of aromatic oximes and four other single aromatic oximes are reported. The loss of H₂O, HO and HCN are major fragmentations from the molecular ion of all the benzaldoximes studies; however, the loss of HCN from the molecular ion did not occur in the oximes of 9-phenanthraldehyde, 1-naphthaldehyde and 2-naphthaldehyde. The halogen substituted benzaldoximes eliminate HCNO and H₂CNO forming an additional fragmentation pathway from the molecular ion. In general, variations were found for each pair of syn- and anti-oximes but no consistent patterns could be found in the spectra for all the syn-isomers versus all of the anti-isomers. The geometric isomerism of four oximes previously reported in the literature have been established for the first time as anti-m-bromobenzaldoxime, syn-9-phenanthraldoxime, syn-1-naphthaldoxime and syn-2-naphthaldoxime. Three new oxime acetates were prepared and their mass spectra are discussed.     

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.     

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.     

Gas Phase Reactions of 1,3,5-Triazine: Proton Transfer,Hydride Transfer,and Anionic σ-Adduct Formation

The gas phase reactivity of 1,3,5-triazine with several oxyanions and carbanions, as well as amide, was evaluated using a flowing afterglow-selected ion flow tube mass spectrometer. Isotopic labeling, H/D exchange, and collision induced dissociation experiments were conducted to facilitate the interpretation of structures and fragmentation processes. A multi-step (→ HCN + HC₂N₂⁻ → CN⁻ + 2 HCN) and/or single-step (→ CN⁻ + 2 HCN) ring-opening collision-induced fragmentation process appears to exist for 1,3,5-triazinide. In addition to proton and hydride transfer reactions, the data indicate a competitive nucleophilic aromatic addition pathway (S_NAr) over a wide range of relative gas phase acidities to form strong anionic σ-adducts (Meisenheimer complexes). The significant hydride acceptor properties and stability of the anionic σ-adducts are rationalized by extremely electrophilic carbon centers and symmetric charge delocalization at the electron-withdrawing nitrogen positions. The types of anion-arene binding motifs and their influence on reaction pathways are discussed.     

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.     

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.     

The fragmentation of aliphatic ketones in the mass spectrometer: A detailed study of nonan-4-one using ion kinetic energy spectroscopy

The ion kinetic energy (IKE) spectra of nonan-4-one, 7,7-d₂-nonan-4-one and 1,1,1-d₃-nonan-4-one have been recorded and interpreted. The various fragmentations observed in the IKE spectra have been confirmed and some new fragmentations found by carrying out high voltage scans with the magnetic field set successively to collect ions at each mass to charge ratio throughout the mass spectrum. Several new fragmentation modes have been discovered, and their significance is discussed.     

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.     

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.     

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.     

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.     

The mass spectra of some pyrazole compounds

The mass spectra of ten pyrazole compounds have been determined. Fragmentation schemes have been derived by means of the metastable defocusing method. The predominant process is cleavage of the nitrogen-nitrogen bond resulting in expulsion of HCN. The process second in prominence is the loss of a nitrogen molecule after initial removal of a hydrogen radical or a substituent, giving the species [C₃H₂R]⁺, probably a cyclopropenyl ion. In general, the fragmentation pattern is strongly influenced by the substituent.     

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.     

Ion chemistry of deprotonated phenylthiocarbamyl-phenylalanine

The fragmentation of an [M-H]^? anion of phenylthiocarbamyl (PTC)-phenylalanine (Phe) and of a deuterium labeled analog using electrospray ionization (ESI) in a negative ion mode was studied. Product ion experiments show that deprotonated PTC-Phe fragments mainly through three different pathways. Further tandem mass spectrometry experiments show that these three pathways actually correspond to the three different deprotonation sites in the molecule. These three ionization sites lead to the losses of, respectively, H₂S and (H₂S+CO₂), C₆H₅N=C=S, and C₆H₅NH₂ from [M-H]^? in the first steps. They yield anions stabilized by resonance. The fragment produced by the loss of C₆H₅NH₂ is relatively weak and originates from a less acidic site. By selecting these fragment anions successively as precursors from the ion source, detailed information on the fragmentation mechanism is obtained. The benzyl-type anion plays a stabilizing role through conjugation. The fragmentation process also involves some uncommon neutral losses. For example, losses of HCN involve reactions that may occur through fouror five-membered cyclic transition states and cyanide ion-molecule complexes. Similar losses of HCN may occur through both the carboxylate anion and one of its tautomeric forms. Deuterium labeling studies support all the mechanistic proposals. The fragments obtained following the loss of the derivatization reagent (C₆H₅N=C=S) show that it is the anion of the deprotonated free amino acid. Preliminary results have shown that this also occurs for other PTC amino acids.     

A Dimer of Hydrogen Cyanide Stabilized by a Lewis Acid

A highly labile dimer of hydrogen cyanide, HCN???HCN, was extracted from liquid HCN by adduct formation with the bulky Lewis acid B(C₆F₅)₃, affording HCN???HCN?B(C₆F₅)₃, which was fully characterized. The influence of the solvent (HCN, CH₂Cl₂, and aromatic hydrocarbons) on the crystallization process was studied, revealing dimer formation when using HCN or CH₂Cl₂ as solvent, whereas aromatic hydrocarbons led to the formation of monomeric arene??HCN?B(C₆F₅)₃ adducts, additionally stabilized by η⁶‐coordination of the aromatic ring system similar to well‐known half‐sandwich complexes.     

The electron-impact-induced fragmentation of some alkyl isocyanides and α-branched alkyl cyanides

The HRP mass spectra of some alkyl isocyanides (R? NC in which R equals CH₃, C₂H₅, n-C₃H₇, n-C₄H₉ and t-C₄H₉) and two methyl branched alkyl cyanides (R? CN in which R equals i-C₃H₇ and t-C₄H₉) have been studied. Using metastable ion transitions and appearance potentials, the fragmentation patterns and spectral characteristics of the isocyanides can be given. A comparison has been made with the mass spectral data of the corresponding cyanides. Although the mass spectra of alkyl cyanides and isocyanides show close relationship, evidence could be obtained that this resemblance is not caused by rearrangement of the isocyanide into cyanide molecules. The main difference between the spectra of both compounds is caused by the strength of the α-bond, being weaker in the case of the isocyanides. The abundance of ions formed by α-bond cleavage decreases with increasing size of the alkyl group.     

Bridgehead nitrogen heterocycles—II: The mass spectra of some pyrazolo[1,5-a]pyridines

Pyrazolo[1,5-a]pyridine undergoes fragmentation upon electron-impact by loss of HCN or C₂H₂N·. In the 2,3-dimethyl derivative loss of HCN and CH₃CN were both observed from the [M – 1]⁺ ion and, in the 3-methyl-2-phenyl derivative, loss of PhCN occurred from the corresponding [M – 1]⁺ ion. Loss of methyl and phenyl radicals was also observed. In 3-acetyl-2-methyl and 3-benzoyl-2-phenyl derivatives, characteristic losses of the CH₃CO· and PhCO· groups were noted. The introduction of a 7-methyl substituent into the six-membered ring had little effect on the fragmentation pattern.