Fragmentation of pyrazolecarbaldehyde thio- and dithioacetals under electron impact and chemical ionization

The mass spectra of 1-substituted 3,5-dimethyl-1H-pyrazole-4-carbaldehyde bis(2-hydroxyethyl) dithioacetals and thioacetals were studied for the first time. The main fragmentation pathways of their molecular ions generated under electron impact and chemical ionization were similar. Primary decomposition of the molecular ions of bis(2-hydroxyethyl) dithioacetals involves elimination of 2-sulfanylethanol molecule with formation of the corresponding 1,3-oxathiolane radical cation. Fragmentation of the molecular ions [M]⁺ · and [M + H]⁺ derived from 2-(3,5-dimethyl-1H-pyrazol-4-yl)-1,4,6-oxadithiocanes includes cleavage of the eight-membered heteroring and elimination of C₄H₉OS ·. Substituents in the heteroring of pyrazolecarbaldehydes inhibit decomposition processes related to the aldehyde group.     

Ammonia chemical ionization mass spectrometry of alcohols: Structural,stereochemical, molecular-size and temperature effects

Ammonia chemical ionization (CI) mass spectra of various open-chain, cyclic and unsaturated C₅- to C₁₀-alcohols were obtained at source temperatures ranging from 60° to 250°C. The reactivity of the ammonia adduct ion MNH and its fragmentation channels are characteristic for substrate structure. Although strongly temperature-dependent, the spectra give nevertheless information on the OH-group environment as well as on the C-skeleton at any source temperature. Primary, secondary and tertiary alcohols as well as allylic and simple olefinic alcohols can be distinguished by their spectra, which show ammonium adduct ions [MNH₄]⁺, adduct dehydrogenation ions [MNH₄-H₂], ammonium substitution ions [MNH₄-H₂O]⁺ and [M-OH]⁺-ions as the main characteristic peaks. Moreover, konfigurational assignments of stereoisomeric alcohols are possible for larger substrate-size and source-temperature ranges than with isobutane CI mass spectrometry. Homologous M NH-ions show molecular-size control of fragmentation and linear MNH-ions are less stable than branched isomers due to incomplete energy randomization.     

Electron-impact induced fragmentation of 2-substituted pyridines and picolines

The fragmentation patterns obtained upon electron impact on 2-nitro-, 2-chloro, and 2-aminopyridines, as well as those of the corresponding 3-, 4-, 5- and 6-picolines were examined. There was considerable departure from those patterns reported for the corresponding benzenoid derivatives. Although the molecular ion from 2-nitro-3-picoline did not show fragment ions attributable to an “ortho-effect” (unlike o-nitrotoluene), those from 2-chloro- and 2-amino-3-picolines did show a loss of HCl and NH₃, respectively. Quite unexpectedly the ions from 2-chloro- and 2-amino-6-picolines also lost HCl and NH₃. Such meta-eliminations for the 2-substituted-6-picolines are postulated to be preceeded by either hydrogen or methyl migration. The mass spectra of 2-pyridone, 2-pyridthione and their respective 3-, 4-, 5- and 6-methyl analogs were also studied. The primary fragmentations of the 2-pyridones were as expected from those reported in the literature. The ions from 3- and 6-methyl-2-pyridones lost water also, the former being another example of an “ortho-effect” observed in this series. Of the thiones, the fragmentations of 3-methyl-2-pyridthione proved most unique since its molecular ion showed besides the loss of HS, the pronounced elimination of H₂S, the latter presumably due to an “ortho-effect.” Figures are presented to illustrate the patterns and metastable ions are indicated when found for the transitions discussed.     

Mass spectrometry of homoadamantane derivatives

Homoadamantane derivatives can be divided into two groups according to their mass spectra. To the first group belong compounds with electron attracting substituents (COOH, CI, COOCH₃, Br); compounds with electron releasing substituents (OCH₃, OH, NH₃, NHCOCH₃) constitute the second group. The most characteristic feature of the first group compounds is the splitting off of the substituent. The hydrocarbon fragment [C₁₁H₁₇]⁺ thus formed then loses olefin molecules with the formation of corresponding ionic species C_11?nH_17?2n. The 3-substituted compounds of this group undergo thermal Wagner-Meerwein type rearrangements into adamantane derivatives, resulting in the [C₁₀H₁₅]⁺ (m/e 135) ion formation; this is the main difference between 1- and 3-substituted homoadamantanes. The series of [C_nH_2n?6X]⁺ ions (where X = OCH₃, OH, NH₂, NHCOCH₃, n = 6 to 10) are characteristic of the mass spectra of the second group compounds, the ion [C₆H₆X]⁺, [M ? C₅H₁₁]⁺ being the most abundant. The intensity ratio of [M ? C₅H₁₁]⁺ to [M ? C₄H₉]⁺ ions is 10:1 for 1-substituted and 3:1 for 3-substituted compounds of this group, allowing the location of the substituent. Some individual features of the spectra are also reported.     

Stereospezifische Fragmentierungen in den Massenspektren von Cyclohexandiaminen und Bis(aminomethyl)cyclohexanen. 33. Mitteilung über massenspektrometrische Untersuchungen,,

Stereospecific Fragmentations in the Mass Spectra of Cyclohexanediamines and Bis(aminomethyl)cyclohexanes The mass spectral behaviour, especially loss of NH₃, of the six isomeric cyclohexanediamines 1--3 (cis and trans each, Scheme 1) as well as of the six isomeric bis(aminomethyl)cyclohexanes 4--6 (cis and trans each, Scheme 6) has been investigated. The cis- and trans-compounds of the 1,2-isomers 1 and 4 show very similar spectra, because of the ease of ring cleavage at C(1)–-C(2) and the similar geometrical relations in all ring conformations. The cis- and trans-compounds of both the 1,3- and 1,4-isomers 2, 3, 5 and 6 show striking differences in their mass spectra due to stereospecific elimination of NH₃ from the molecular ion.     

Mass spectra of monosubstituted trans-stilbenes

The mass spectra of twenty-eight monosubstituted trans-stilbenes in ortho, meta, para and alpha positions with ? N(CH₃)₂, ? NH₂, ? OCH₃, ? OH, ? Br, ? Cl, ? F, ? CH₃, ? COOH, ? CN and ? NO₂ groups as substituents have been studied. A detailed fragmentation pathway is given for stilbene. This fragmentation, characteristic for most of the substituted stilbenes, takes place either from the molecular or from the [M - Substituent] ion. In o-nitro-, o-methoxy-,α-carboxyl- and α-methylstilbene, however, rearrangement reactions prior to fragmentation influence the fragmentation pattern.     

Stabilization of even-electron ions by cyclization of substituents on 3N- and 4N-nitrogens in 4N-substituted cytosines

Electron impact mass spectra of 4N-substituted derivatives of cytosine are reported. The strong influence of 4N-substituents on the mode of mass fragmentation occurring upon electron impact ionization was proved. The presence of α-carbon in the 4N-substituent extends the possibilities of fragmentation via rearrangement leading to formation of even-electron bicyclic ions containing quaternary 3N-nitrogen. When β-carbon was present in the 4N-substituent, the decomposition based on elimination of alkenes was detected as well as the rearrangement leading to formation of bicyclic even-electron ions containing quaternary 3N- or 4N-nitrogen.     

Structural characterization of 1,3,4-thiadiazolo[3,2-a][1,3,5]triazines by electron impact mass spectrometry

The electron-impact-induced fragmentation of eleven 1,3,4-thiadiazolo[3,2-a][1,3,5]triazines was investigated with the aid of exact mass measurements, B/E and B²/E linked scans, and deuterated compounds. The dominating breakdown process in the electron impact mass spectra of 2-substituted 6-phenyl-1,3,4-thiadiazolo[3,2-a]-[1,3,5]triazine-5,7-diones (1–5) is a retro-Diels-Alder reaction. This process gives rise to the base peak, whereas the molecular ions are of very low intensity. In the mass spectra of 2-substituted 7-methylthio-1,3,4-thiadiazolo-[3,2-a][1,3,5]triazine-5-ones (6–11) in which this fragmentation cannot occur because of the two conjugated double bonds in the triazine ring, the molecular ions are very intense. The mass spectral data permits an unequivocal structure assignment to these compounds, which are otherwise difficult to characterize.     

Electron-impact induced rearrangements in isomeric pyridine aldoximes

The mass spectra of α-, β- and γ-pyridine aldoximes and the respective O-methyl ethers were studied. The mass spectral behaviour of α-pyridine aldoxime is characterized by the elimination of NO, while the molecular ion of the γ-isomer expels H₂ CN. In the case of the β-isomer the formation of the m/e 67 ion (C₄H₅N) in a concerted process is the main feature. In the α-pyridine aldoxime methyl ether, in sharp contrast to the hydroxy analog, the M-30 peak was found to be due to the elimination of CH₂O, the expulsion of NO being absent. The mechanism of the fragmentation reactions is discussed, the conclusion drawn being based on the high resolution measurements as well as on the spectra of the respective deuterioanalogs and on the metastable transitions.     

Electron-impact fragmentation of N-substituted 2-aminobenzoxazoles and 2-aminobenzothiazoles

The mass spectra of twenty-eight N-substituted 2-aminobenzoxazoles and 2-aminobenzothiazoles have been recorded and the identity of various ions in the mass spectra have been established by high resolution measurement. The molecular compound of series, benzoxazole, undergoes loss of hydrogen cyanide and carbon monoxide from the molecular ion as the most important decomposition pathways. The mass spectra of N-substituted benzothiazoles showed a similar fragmentation as that of N-substituted benzoxazoles.     

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 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.     

Features of the behavior of 5-substituted N(3)-acyl-4,6-diaryl-3,4-dihydropyrimidin-2(1H)-ones under electron ionization

Mass spectra of 5-substituted N(3)-acyl-4,6-diaryl-3,4-dihydropyrimidin-2(1H)-ones are studied. The features of the dissociative ionization of their molecular ions, which occurs with ketene elimination from the acyl group, are revealed. The subsequent fragmentation of fragment ions proceeds according to the rules established for pyrimidin-2(1H)-one derivatives.     

Heterocyclic studies—XXVIII Mass spectra of some 5-trifluoromethylpyrimido-(5,4-e)as-triazines

Fragmentation of 7-substituted 5-trifluoromethylpyrimido(5,4-e)as-triazines is dominated by consecutive losses of N₂ and HCN from the triazine ring. Deuterium labelling, accurate mass measurements and spectral changes with substitution patterns confirm the fragmentation pathways. Comparison of the spectra with those of corresponding pteridines indicates that the 1,2,4-triazine ring fragments much more readily than the pyrazine ring.     

Ring contractions of dihydro- and tetrahydro-1,5-benzodiazepines in electron ionization mass spectrometry

Electron ionization mass spectra of a series of 2,4-disubstituted dihydro- and tetrahydro-1,5-benzodiazepines are discussed. The fragmentation of these compounds is dominated by ring contractions of diazepine, which give both five- and six-membered rings, benzimidazoles and quinoxalines. Tetrahydro compounds showed a tendency to eliminate one nitrogen from the ring system and give quinoline rings through NH₂ and NH₄ eliminations. The electron ionization spectra of cis and trans isomers of tetrahydro compounds are identical.     

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).     

Mass-analysed ion kinetic energy and collisionally induced dissociation mass spectra of clusters of acetylated xylo-oligosaecharides with protonated ammonia and methylannine

Per-O-acetylated methyl glycosides of D -xylan-type di- and trisaccharides were studied by mass-analysed ion kinetic energy (MIKE) and collisionally induced dissociation (CID) mass Spectrometry using protonated ammonia and methylamine, respectively, as reaction gases in chemical ionization (CI). The oligosaccharides form abundant cluster ions, [M + NH₄]⁺ or [M + CH₃NH₃]⁺, and the main fragmentation of these ions in the MIKE and CID spectra is the cleavage of interglycosidic linkages. Thus, CI (NH₃) or CI (CH₃NH₂) spectra in combination with the MIKE or CID spectra allow the molecular masses, the masses of monosaccharide units and the branching point in oligosaccharides to be established. In the case of disaccharides, it is possible to distinguish the (1 → 2) linkage from the other types of linkages.     

Investigation of azoles and azines. 76. Mass spectra of 5- and 6-substituted uracils

Peaks of molecular ions that generally have the maximum intensity are observed in the mass spectra of most of the investigated 5- and 6-substituted uracils and 5-substituted orotic acids and their deutero analogs and methylated derivatives. The principal pathway of the fragmentation of the molecular ions is retrodiene fragmentation with the formation of [O=C₍₄₎C₍₅₎R⁵C₍₆₎R₍₆₎N₍₁₎R¹]⁺ (F₁) ions. The stabilities of the latter depend on the nature and position of the substituents attached to the C₍₅₎ and C₍₆₎ atoms. The fragmentation of the F₁ ions can be realized via four principal pathways (B-E) with the detachment of N-CR⁶ (B), O=C=CR⁵ (C), CO (D), and R⁶ (E) fragments. The most general pathway for the fragmentation of 5-substituted uracils is pathway C, whereas the most general pathway for 6-substituted uracils is pathway E. In the spectra of 5-substituted orotic acids the intensities of the molecular-ion peaks are high (100%) only in the case of electron-donor R⁵ and decrease sharply with an increase in the electron-acceptor strength of the substituent. The principal pathways of fragmentation of the molecular ions are decarboxylation (F) and retrodiene fragmentation (A), the contribution of which is appreciably smaller. The M-CO₂ ions formed after decarboxylation undergo fragmentation via a scheme similar to that observed for 5-substituted uracils.See [1] for Communication 75.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 520–531, April, 1990.     

Massenspektrometrische Fragmentierungen β-Substituierter Adamantanone und Adamantandione

High resolution mass measurements and defocused metastable ion detection have been employed in an investigation of the electron-impact-induced fragmentation of a series of β-substituted adamantanones and adamantanediones. Whereas the isomeric bromo-, iodo- and thiocyanato-adamantanones give almost identical spectra, the fragmentation of the fluoro and chloro derivatives is dependent on whether the substituents are ‘axial’ or ‘equatorial’. Hydroxy- and acetoxy-adaman-tanones exhibit rather complex mass spectra. Adamantanediones, substituted in the β-position by various COR- and NR₁R₂-groups, exhibit characteristic ion peaks which are formed by McLafferty rearrangement and α-cleavage with subsequent elimination of carbon monoxide and allylic bond fission. The mass spectral behaviour of the isomeric hydroxy-carbomethoxy-adamantanones and dihydroxy-adamantanes is determined by the orientation of the functional groups.     

Proximity effects in the mass spectra of crowded bis(dimethylamino)arenes: Part II—Rearrangements of the molecular radical cations of ‘proton sponges’ by reciprocal methyl/hydrogen transfer

The EI induced fragmentation pathways of 4,5-bis(dimethylamino)fluorene, 4-(d₆-dimethylamino)-5-(dimethylamino)fluorene, 4,5-bis(d₆-dimethylamino)fluorene, 4-(dimethylamino)-5-methylaminofluorene, 4,5-bis-(methylamino)fluorene, 4-amino-5-methylaminofluorene, 1,8-bis(dimethylamino)naphthalene, 1,8-bis(d₆-dimethyl-amino)-naphthalene and 1,8-bis(dimethylamino)-2,7-dimethoxynaphthalene were investigated. A mechanism is pro-posed for the surprising elimination of CH₃? NH₂ from the molecular ion, followed by loss of C₂H₅·, C₂H₄ and CH₃CN and for the accompanying cyclizations to stable heterocyclic ions: prior to fragmentation the molecular radical ion rearranges to new, distonic radical ions by reciprocal H and CH₃ transfers between the adjacent dimethylamino groups. Each of these new, isomeric molecular ions decomposes subsequently in a characteristic way.