Mass spectral fragmentation of benzofurazan-1-oxide

Fragmentations in the mass spectrum of benzofurazan-1-oxide have been studied using linked scan, accelerating voltage scan and mass-analysed ion kinetic energy spectrometric techniques. Major pathways involve NO·+ NO· and NO·+CO loss, these double losses occurring in such rapid succession as to appear ‘concerted’ in some experiments. Minor pathways are loss of CO₂, C₂N₂O₂, or C₂HN₂O₂ from the molecular ion. The major fragment ion, m/z 76, in the conventional mass spectrum is not detected in a mass-analysed ion kinetic energy spectrometric experiment with the molecular ion until collision activation is provided. The conventional electron impact spectrum invariably includes ions from benzofurazan which is produced by thermal deoxygenation in the source.     

Positive and negative ion mass spectra of Aryl-ONN-azoxy compounds containing electron withdrawing groups

The positive and negative ion mass spectra, at 70 eV, of p-RC₆H₄N(O)?NCOOCH₃ (R?H, Cl, Br, NO₂), C₆H₅N(O)?NCOOC₂H₅, p-RC₆H₄N(O)?NCONH₂ (R?H, Cl, Br, NO₂) and p-RC₆H₄N(O)?NCOC₆H₅ (R?H, Cl, Br, NO₂) are reported. The azoxyester derivatives show abundant molecular ions and a number of weak fragment and rearrangement ions in the positive ion mass spectra, whereas weak molecular ions and abundant low mass fragment ions are present in the negative ion mass spectra. Similar behaviour is observed in the mass spectra of the azoxyamides. Conversely, for the azoxycarbonyl compounds the positive molecular ion is absent. A ready cleavage of the N? CO bond occurs and only few fragments of low diagnostic value are formed, whereas the negative molecular ion is the base peak for all these compounds with the exception of the p-NO₂ derivative, where [M? O]^?? is the base peak and [M]^?? is the second major ion. The behaviour under electron impact of these classes of compounds is compared with that of azoxycyanides reported previously.     

Rearrangements in the molecular ion of o-(methyl-d3-thio)benzoic Acid: Comparison with o-methoxy-d3-benzoic acid

Hydrogen/deuterium exchange and rearrangements in the molecular ion of o-(methyl-d₃-thio)benzoic acid lead to fragment ions [M? OD]⁺ as well as [M? OH]⁺ and m/z 106 and 107, just as in the molecular ion of o-methoxybenzoic acid. However, the fragment ion m/z 108 has the composition C₆H₄S rather than C₆H₂D₃CO as it does in the case of o-methoxy-d₃-benzoic acid. By varing the repeller potential at 10 eV (and thus the residence time in the ion source), the corresponding fragments are seen to be formed more slowly from the methylthio acid than from the methoxy acid, which leads to the conclusion that H/D exchange between carboxyl and labelled methylthio is slower than it is between carboxyl and labelled methoxyl.     

Ion chemistry of phthalamic acids. 2—mass spectral retrosynthesis of phthalanilic acids and structure analysis of [C8H6NO2]+ ions from N-cyclohexylphthalamic acid and [MH]+ of N-cyclohexylphthalimide

Under electron impact o-phthalanilic acids show the retrosynthetic reaction previously described for other phthalamic acids. As primary amine derivatives they undergo thermal and electron impact induced water loss. Like the molecular ions of the related phthalimides, their [M? H₂O]^+˙ do not give [C₈H₆NO₂]⁺ fragments, which are obtained from the N-cyclohexyl derivative. The structure of such fragments is investigated by collisionally activated mass analysed ion kinetic energy spectra, and compared with the [MH]⁺ of phthalimide, obtained by chemical ionization with CH₄ or NH₃ and assumed to be possible models.     

Determination of the fragmentation mechanisms of organophosphorus ions by H2O and D2O atmospheric-pressure ionization tandem mass spectrometry II—dialkyl alkylphosphonate ions

Diethyl methylphosphonate (DEMP), diisopropyl methylpbosphonate (DIMP), diethyl isopropylphosphonate (DEIP) and diethyl ethylphosphonate (DEEP) were characterized by H₂O and D₂O atmospheric pressure ionization tandem mass Spectrometry (API-MS/MS). Collision-induced dissociation (CID)/fragmentation pathways included alkyl ions by direct cleavage, alkyl radical and water loss processes and McLafferty and McLafferty-type rearrangements by six- and five-membered ring transition states, respectively. D₂O API proved particularly useful in that certain decomposition pathways (i.e. water and methanol neutral losses) had a statistical distribution as to the loss of an acid deuteron and proton(s). This phenomenon was manifested by two pairs of ions in the D₂O API daughter-ion mass spectrum for each phosphonate compound (e.g. both m/z 79/80 and 65/66 for DEMP and DIMP). The observed ion intensity ratios for these pairs of ions served as guides in the determination of their predicted ion relative abundance ratios and CID decomposition pathways. Water neutral losses as opposed to ether and alcohol neutral losses were favored for most of the protonated organophosphonate molecular ion decomposition schemes.     

Electron impact studies. CXXIV—Negative ion mass spectra of organic functional groups. Thioacetanilides

The thioacetanilide negative molecular ion (produced by secondary electron capture) is stable, but it fragments after collisional activation to yield [C₆H₅NH]^? by cleavage α to the C?S grouping. The negative molecular ions of (substituted) o-nitrothioacetanilides undergo a series of extremely complex rearrangement reactions. For example, the molecular anion derived from o-nitro-N-methylthioacetanilide yields both acetate and thioacetate anions as major fragment ions.     

Identification of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) pyrolysis products by simultaneous thermogravimetric modulated beam mass spectrometry and time-of-flight velocity-spectra measurements

The pyrolysis products formed during the isothermal decomposition of HMX at 211°C are H₂O, HCN, CO, CH₂O, NO, N₂O, methylformamide, C₂H₆N₂O, octahydro-1-nitroso-3,5,7-trinitro-1,3,5,7-tetrazocine, and a nonvolatile residue. The temporal behaviors of these products during the decomposition are presented. The method for using time-of-flight (TOF) velocity spectra to assist mass-spectrometry measurements in identifying the different gaseous products formed from the pyrolysis of a material by determining the approximate molecular weights of the different gaseous products contributing to the different m/z values in the mass spectrum of the mixture is described. The ion fragmentation of HMX as a function of electron energy shows complete fragmentation of the HMX molecular ion for electron energies ≥ 12.4 eV. No fragments from the pyrolysis of HMX other than those mentioned above are observed.     

Fragmentation of certain substituted azadispiro(5.1.5.2)pentadec-9-ene and azadispiro(4.1.4.2)tridec-8-ene derivatives under electron ionization

A study of the electron ionization mass spectra of certain azadispiro(5.1.5.2)pentadec-9-ene-7,15-diones and azadispiro(4.1.4.2)tridec-8-ene-6,13-diones and their derivatives has revealed that these molecules undergo fragmentation primarily by two routes, viz. loss of CO and elimination of the substituent on the pyrrolidine nitrogen. Under positive ionization conditions loss of CO is the predominant process in the diones as it releases the ring strain, while in the 6- or 7-ols loss of the substituent on nitrogen is the favoured pathway. The further decomposition pathways of these primary fragments [M ? CO]⁺˙ and [M ? OR³]⁺ have been delineated with the help of high-resolution mass measurements, D₂O exchange and metastable spectra, These compounds give very simple negative ion spectra showing only [M ? OR³]^? and [NCO]^? ions except the N-hydroxy compounds which show [M ? H]^? ions as well.     

An energy-resolved study of the fragmentation of ionized 1-Penten-3-ol

A detailed energy-resolved study of the fragmentation of CH₂?CHCH(OH)CD₂CD₃ (1-d₅) has been carried out using metastable ion studies and charge exchange techniques, combined with collision-induced dissociation studies to establish the structures of fragment ions. At low internal energies (metastable ions) the molecular ion of 1-d₅ rearranges to the 3-pentanone structure and fragments by loss of C₂H₅ or C₂D₅ leading to the acyl structure, [CH₃CH₂C?O]⁺ or [CD₃CD₂C?O]⁺, for the fragment ion. However, with increasing internal energy of the molecular ion this rearrangement process decreases rapidly in importance and loss of C₂D₅ by direct cleavage, leading to [CH₂?CHCH?OH]⁺, becomes the dominant fragmentation reaction. As a result the [C₃H₅O]⁺ ion seen in the electron impact mass spectrum of 1-penten-3-ol has predominantly the protonated acrolein structure.     

Origin of the [C4H9O]+ ions in the mass spectrum of n-butyl ethyl ether

The mechanisms of formation of m/z 73 ions in the mass spectrum of the ionized title compound were investigated by deuterium substitution and by examining the decompositions of metastable ions. Two routes to the [C₄H₉O]⁺ ions were found in the normal spectrum. The ethyl lost by the major pathway contains the α- and β-hydrogens and a γ-hydrogen from the butyl group. The minor route involves the loss of ethylene from the [M? H]⁺ ion. There were metastable peaks for losses of ethyl, ethanol and methyl from the molecular ion. The ethyl contains the α- and β-methylenes and a γ-hydrogen, while the methyl is the δ-methyl of the butyl group. The labeling data rule out a previous mechanistic proposal for the loss of ethyl and support a mechanism involving stepwise isomerization to the sec-butyl ethyl ether molecular ion. However, the metastable ion chemistries of the molecular ions from the n- and sec-butyl ethyl ethers are highly dissimilar, perhaps due to decompositions from different electronic states. The n-pentyl methyl ether ions loses both ethyl and propyl, apparently following rearrangements to the 3-pentyl and 2-pentyl ether ions. Di n-butyl and n-butyl methyl ethers also give metastable peaks for loss of methyl, ethyl and the shorter chain alcohol.     

The mass spectral fragmentation of phenyl ω-dialkoxyethyl tellurides

The 70 eV mass spectrum of phenyl ω-dimethoxyethyl telluride [C₆H₅? Te? CH₂CH(OR)₂, R?CH₃]contains an intense peak at m/z 238 which corresponds to a rearrangement ion [C₆H₅? Te? OR]⁺. The formation of this species is further illustrated by the presence of a peak at m/z 241 in the spectrum of the hexadeuterated analog (R?CD₃) and a peak at m/z 252 in the spectrum of the ethyl analog (R?CH₂CH₃). These combined results illustrate the presence of only one of the alkoxyl groups in the rearrangement ion. Several other abundant ions that contain oxygen but not tellurium are present in the spectra of these compounds. High resolution analyses have aided in the determination of the origin and composition of several of the characteristic ions formed upon electron impact fragmentation of phenyl ω-dimethoxyethyl telluride.     

Specific and random fragmentations in the mass spectra of some neopentyl compounds

The mass spectra of neopentyl alcohol, bromide and chloride and some ¹³C and ²H labelled analogues have been studied. Most fragmentations of the molecular ions of these compounds occur by simple bond cleavages and do not involve rearrangement before fragmentation. We propose that in the [M ? CH₃]⁺ fragment ions, seven of the eight hydrogen atoms and all four carbon atoms are involved in randomisation when an ethylene molecule is ejected. The eighth hydrogen atom (which comes from a methyl group) is probably associated with the heteroatom. The neopentylcation, observed only in the mass spectrum of the bromide, fragments mainly by loss of an ethylene molecule, also containing randomly selected hydrogen and carbon atoms. The [C₄H₇]⁺ ion also was observed to undergo complete atom scrambling.     

Electron impact induced fragmentation of some 7-(o- and p-R-benzylidene)-3-(o- and p-R-phenyl)-3,3a,4,5,6,7-hexahydro-2H-indazoles. I

The mass spectral fragmentation patterns of ten 7-(o- and p-R-benzylidene)-3-(o- and p-R-phenyl)-3,3a,4,5,6,7-hexahydro-2H-indazoles, I, obtained by electron impact have been studied. All the spectra analyzed contain molecular ions and the principal fragmentation routes take place either from the molecular ion, or from (M⁺-1) ion. Likewise, our investigation of the mass spectra of these compounds revealed interesting relationships between the substitution pattern in the framework of I and the fragmenation pathways.     

Massenspektren von sekundären Vinylcarbinolen

The mass spectra of secondary vinylcarbinols of the structure R? CH(OH)? CH?CH₂ show the same fragments as those of the isomeric ethylketones R? CO? C₂H₅. This is the result of a rearrangement of the molecular ions of the vinylcarbinols to molecular ions of the ethylketones before fragmentation occurs. Compounds of the two classes differ only slightly from one another in the intensity values.     

An experimental and computational investigation on the fragmentation behavior of enaminones in electrospray ionization mass spectrometry

The dissociation pathways of protonated enaminones with different substituents were investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) in positive ion mode. In mass spectrometry of the enaminones, Ar? CO? CH?CH? N(CH₃)₂, the proton transfers from the thermodynamically favored site at the carbonyl oxygen to the dissociative protonation site at ipso‐position of the phenyl ring or the double bond carbon atom adjacent to the carbonyl leading to the loss of a benzene or elimination of C₄H₉N, respectively. And the hydrogen? deuterium (H/D) exchange between the added proton and the proton of the phenyl ring via a 1,4‐H shift followed by hydrogen ring‐walk was witnessed by the D‐labeling experiments. The elemental compositions of all the ions were confirmed by ultrahigh resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR‐MS/MS). The enaminones studied here were para‐monosubstituted on the phenyl ring and the electron‐donating groups were in favor of losing the benzene, whereas the electron‐attracting groups strongly favored the competing proton transfer reaction leading to the loss of C₄H₉N to form a benzoyl cation, Ar‐CO⁺. The abundance ratios of the two competitive product ions were relatively well‐correlated with the σ_p⁺ substituent constants. The mechanisms of these reactions were further investigated by density functional theory (DFT) calculations. Copyright © 2010 John Wiley & Sons, Ltd.     

Ortho effects in organic molecules on electron impact. 12—Mechanism of the H2O loss from the molecular ion of 2-(phenylamino)benzoic acid

The mass spectrum of 2-(phenylamino)benzoic acid is characterized by the presence of the base peak at m/z 195, formed by the expulsion of H₂O from the molecular ion. A mechanism for the water loss, involving the ? COOH and ? NH functions followed by cyclization leading to the molecular ion of acridone, is proposed based on the study of the substituted derivatives and MIKE spectra.     

Structure determination of some C4H5N+˙ Ions from substituted pyridines by collisionally activated dissociation mass spectrometry

A standard procedure for recording and correcting collisionally activated dissociation mass spectra is proposed, and used to distinguish between the C₄H₅N^+˙ ions formed from hydroxy- and amino-pyridines after loss of CO and HCN, respectively. It is concluded that these ions are cyclic. From the 4-isomers the 3H-pyrrole ion is formed whereas from 2-hydroxypyridine the 1H-pyrrole ion is formed. In the other cases, mixtures of 2H- and either 1H- or 3H-pyrrole ions are generated, depending on the nature of the precursor.     

Fragmentation of 2‐aroylbenzofuran derivatives by electrospray ionization tandem mass spectrometry

We investigated the gas‐phase fragmentation reactions of a series of 2‐aroylbenzofuran derivatives by electrospray ionization tandem mass spectrometry (ESI‐MS/MS). The most intense fragment ions were the acylium ions m/z 105 and [M+H–C₆H₆]⁺, which originated directly from the precursor ion as a result of 2 competitive hydrogen rearrangements. Eliminations of CO and CO₂ from [M+H–C₆H₆]⁺ were also common fragmentation processes to all the analyzed compounds. In addition, eliminations of the radicals •Br and •Cl were diagnostic for halogen atoms at aromatic ring A, whereas eliminations of •CH₃ and CH₂O were useful to identify the methoxyl group attached to this same ring. We used thermochemical data, obtained at the B3LYP/6‐31+G(d) level of theory, to rationalize the fragmentation pathways and to elucidate the formation of E , which involved simultaneous elimination of 2 CO molecules from B .     

Mass spectral and NMR studies of some cinnolines

Fragmentation upon electron impact of cinnoline (1) occurs with the consecutive loss of N₂ and C₂H₂. Fragmentation of 4,4′-dicinnolyl (2) and 4-styrylcinnoline (4) gives a series of ions leading to the “dibenzoladderene” ion (3) and the 1-phenylbenzodibutylene ion (5) respectively. Fragmentation of 4-styrylquinoline (6) also leads to 5 , but of more interest is the loss of H. during ring rearrangement to give the highly resonance stabilized 3-styrylbenzocyclo-pentadieneoneimine ion (7) which then loses N. Fragmentation of various other substituted cinnolines follow different pathways: 4-methylcinnoline (8) apparently fragments through the “1,2-diazatropylium” ion (9) ; nitrocinnolines fragment with initial loss of the nitro substituent; aminocinnolines fragment with initial loss of N₂; and 4-cinnolone (17) fragments with the consecutive loss of two HCN's and CO. The NMR spectra of cinnolines generally show the following order of deshielding: 3-proton > 8-proton > 4-proton. The spectra of cinnolinum chloride (18) is interpreted in terms of protonation at N-1 of 1 , and the spectrum of 17 is interpreted in terms of strong intermolecular hydrogen bonding.     

Fragmentation of organosulfur compounds upon electron impact. Part III. Metastable decomposition of the molecular ions of methyl thioglycolate and ethyl thioglycolate

The metastable decompositions of the molecular ions of methyl thioglycolate (1) and ethyl thioglycolate (2) were investigated by means of mass analyzed ion kinetic energy (MIKE) spectra and deuterium labeling. The loss of methanol is the only metastable decomposition of 1^+·. This fragmentation occurs via two distinct pathways. The molecular ions of 2 decompose in a variety of ways, i.e., the losses of water, ethene, ethanol or ?₂H₃O₂. All of these decompositions, except the loss of ethene, occur through two distinct mechanisms. During the loss of ?₂H₃O₂, the ethyl group or ethene migrates from the oxygen to the sulfur atom. The loss of H?S, which corresponds to the loss of H?O with a concomitant double hydrogen transfer observed in the case of methyl glycolate (3), does not participate in the metastable decomposition of 1^+· and 2^+·. This is due to the energetic favorableness of the loss of methanol.