Studies in chemical ionization mass spectrometry: Aryl Ketones

The CI mass spectra of aryl ketones, πCOR, were studied and found to give primarily [M + 29]⁺, [M + 1]⁺, [M ? 1]⁺, [πCO]⁺ and [RCO]⁺ ions. The major change in the spectra with increasing length of the aliphatic side chain was an increase in the [M ? 1]⁺/[M + 1]⁺ ratio. Increasing sample size was reflected primarily in the formation of [2M + 1]⁺ ions and a decrease in [M + 1]⁺ ions. Small amounts of water in the reactant gas reduced the extent of fragmentation action.     

Hydrogen transfer in the retro diels–alder fragmentation of oxygen-containing heterocyclic compounds. II—Chromones

Mass Spectra of unsubstituted, 2-methyl-, 3-methyl and 2,3-dimethylchromones were examined. These compounds showed [RDA]⁺˙ and [RDA + H]⁺ ions as characteristc ions, together with [M? H]⁺,[M? CO]⁺˙,[M? CHO]⁺ and [RDA? CO]⁺˙ ions. Based on deuterium labelling experiments and measurement of metastable peaks by the ion kinetic energy defocusing technique, the origin of transferred hydrogen in the [RDA + H]⁺ ion was clarified. The mechanism of the [RDA + H]⁺ ion formation is discussed.     

Translational energy release and stereochemistry of steroids. VIII-The mechanism of the elimination of water from metastable ions in epimeric 3-hydroxy steroids of the 5α-series

The mechanism of water elimination from metastable molecular, [M ? CH₃˙]⁺ and [M ? ring D]⁺˙ ions of epimeric 3-hydroxy steroids of the 5α-series has been elucidated. Deuterium labelling, the measurement of the translational energy released during the loss of water, and collision-induced decomposition mass-analysed kinetic energy spectrometry were the techniques used. It was found that the mechanisms of water loss from metastable M⁺˙ and [M ? ring D]⁺˙ ions is different from that from [M ? CH₃˙]⁺ ions.     

Mass spectra of chlorinated aromatics formed in pulp bleaching: I—chlorinated catechols

A systematic study on the electron impact mass spectra of all nine chlorinated catechols in presented. Metastable ion analysis was used to elucidate the fragmentation pathways. The influence of the position of the chloro substituents can be used to distinguish the structural isomers. In this respect the most characteristic fragment ions are [M? CHl]⁺˙, [M? HCOOH]⁺˙, [M? COCl]⁺, [M? HCl? CO]⁺˙, [M? CHOCl]⁺˙ and [M? HCl? HCl]⁺˙.     

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 spectra of aliphatic dicarboxylic acids and their dimethyl esters: Cyclic structures for the [M − H2O]+˙ ions from the diacids and [M − MeOH]+˙ ions from the dimethyl esters

Methyl 2-oxocycIoalkane carboxylate structures are proposed lor the [M ? MeOH]^+˙ ions from dimethyl adipate, pimelate, suberate and azelate. This proposal is based on a comparison of the metastable ion mass spectra and the kinetic energy releases for the major fragmentation reaction of these species with the same data for the molecular ions of authentic cyclic β-keto esters. The mass spectra of α,α,α′,α′-d₄-pimelic acid and its dimethyl ester indicate that the α-hydrogens are involved only to a minor extent in the formation of [M ? ROH]^+˙ and [M ? 2ROH]^+˙ ions, while these α-hydrogens are involved almost exclusively in the loss of ROH from the [M ? RO˙]⁺ ions (R = H or CH₃). The molecules XCO(CH₂)₇COOMe (X = OH, Cl) form abundant ions in their mass spectra with the same structure as the [M ? 2MeOH]^+˙ ions from dimethyl azelate.     

Structural determination of modified fatty acids by collisional activation of cationized molecules

The nature and location of a variety of modifications of fatty acids are determined by collisional activation (CA) of [M + 2Li ? H]⁺ ions. The sample molecules are cationized in situ on the probe tip, desorbed by fast atom bombardment and, upon CA, undergo charge-remote decompositions. This approach is a direct, totally instrumental method for structure elucidation. Advantages of CA of [M + 2Li ? H]⁺ ions are that fatty acids with substituents in close proximity to the carboxylate terminus and modified short-chain acids are readily determined: decompositions of carboxylate anions of these fatty acids result in collision-activated dissociation (CAD) spectra that give incomplete structural information. However, the CAD spectra of some [M ? H]^? ions, such as those from epoxy acids, are simpler to interpret than those of the [M + 2Li ? H]⁺ ions. Thus, CA of fatty acid [M + 2Li ? H]⁺ ions is a complementary approach to CA of [M ? H]^? ions for determining the fatty acid structures investigated here. The use of this approach for analyzing complex mixtures of modified fatty acids is also evaluated.     

Cyclic organophosphorus compounds. XVIII—the mass spectroscopy of some 2-amino-1,3,2-dioxaphosphorinans,cyclic phosphorodiamidates and phosphorodiamidothionates

Stepwise replacement of O in 1,3-dioxa-2-phospha(V)-cyclohexanes (or related ring systems) by NR (R=H or Me) leads to an increase in the stability of the hetero-ring ions produced under electron impact conditions. In the case of the 2-phenoxy derivatives, there is also an increased abundance of [M? PhO]⁺ or [M? PhOH]⁺ ions, and, for the 2-sulphides, a reduction in the abundance of [M-S]^+˙ and [M-SH]⁺ ions, with a concurrent increase in that of [M-PhS]⁺ ions. Such trends have been correlated with ultraviolet photoelectron spectral data on a qualitative basis.     

Mass spectra of sulfinamide derivatives and identification of their thermal decomposition products

The mass spectra of 30 sulfinamide derivatives (RSONHR', R' alkyl or p-XC₆H₄) are reported. Most of the spectra had peaks attributable to thermal decomposition products. For some compounds these were identified by pyrolysis under similar conditions to be: RSO₂NHR', RSO₂SR, RSSR and NH₂R' (in all kinds of sulfinyl amides); RSNHR' (in the case of arylsulfinyl arylamides); RSO₂C₆H₄NH₂, RSOC₆H₄NH₂ and RSC₆H₄NH₂ (in the case of arylsulfinyl arylamides of the type of X = H) The mass spectra of the three thermally stable compounds showed that there are several kinds of common fragment ions. The mass spectra of the thermally labile compounds had two groups of ions; (i) characteristic fragment ions of the intact molecules and (ii) the molecular ions of the thermal decomposition products. It was concluded that the sulfinamides give the following ions after electron impact: [M]⁺, [M ? R]⁺, [M ? R + H]⁺, [M ? SO]⁺, [RS]⁺, [NHR']⁺, [NHR' + H]⁺, [RSO]⁺, [RSO + H]⁺, [R]⁺, [R + H]⁺, [R']⁺ and [M ? OH]⁺, and that the thermal decomposition products give the following ions: [RSO₂SR]⁺, [RSSR]⁺, [M ? O]⁺, [M + O]⁺ and [RSOC₆H₄NH₂]⁺.     

Electron impact mass spectra of polycyclic aromatic compounds with several types of pyridino- and benzobenzanthrone skeletons

Electron impact mass spectra were measured for five isomers of pyridinobenzanthrones and three isomers of benzobenzanthrones. The fragmentation pattern and intensity of M²⁺, [M – H]⁺, [M – CO]ⁱ⁺, [M – CO – H(or 2H)]ⁱ⁺ and [M – CO – HCN]ⁱ⁺ (i = 1, 2) ions indicated remarkable differences and very interesting features according to the isomers with or without nitrogen and condensation positions of a pyridino or benzo ring to the benzanthrone skeleton. Further, the competition of decompositions through [M – H]⁺, [M – CO]^+˙ or [M – HCN]^+˙ ions was confirmed by the observation of metastable ions and the appearance energies of fragment ions. Interesting observations from these results were expulsion of an H atom in close proximity to the area around an O?C group, a weak bonding interaction between sp² C? H and an O?C group, inducing specific hydrogen rearrangement, and characteristic charge localization on heteroatoms.     

Ion-molecule reactions observed for nitroaromatic compounds in negative ion fast atom bombardment mass spectrometry

Analyses of a series of nitroaromatic compounds using fast atom bombardment (FAB) mass spectrometry are discussed. An interesting ion-molecule reaction leading to [M + O ? H]^? ions is observed in the negative ion FAB spectra. Evidence from linked-scan and collision-induced dissociation spectra proved that [M + O ? H]^? ions are produced by the following reaction: M + NO₂^? → [M + NO₂]^? → [M + O ? H]^?. These experiments also showed that M^?˙ ions are produced in part by the exchange of an electron between M and NO₂^? species. All samples showed M^?˙, [M ? H]^? or both ions in their negative ion FAB spectra. Not all analytes studied showed either [M + H]⁺ and/or M⁺˙ in the positive ion FAB spectra. No M⁺˙ ions were observed for ions having ionization energies above ～9 eV.     

The [M?OH]+ ions of m- and p-ethylnitrobenzene: A common structure?

The structures of the [M? OH]⁺ ions of m- and pethylnitrobenzene have been compared by measurements of metastable ion spectra, collisional activation spectra, kinetic energy releases and critical energies for the formation of these ions and their subsequent decomposition. Normalized rates of fragmentation of metastable molecular ions and metastable [M? OH]⁺ ions have been compared for ion lifetimes up to 30 μs. The energy measurements fail to distinguish between the structures of the [M? OH]⁺ ions, but the normalized fragmentation rates and the collisional activation spectra show their structures to be different.     

Electron impact mass spectra of some dioximes of o-diacyl benzenes

The electron impact mass spectra of the new synthesized dioximes of o-diacyl benzenes (2) are reported. In addition to the molecular ion, characteristic peaks appear at values corresponding to the [M ? OH] ⁺, [M ? NOH]⁺ and [M ? NHOH]⁺ ions. No initial dehydration of the molecular ion has been observed.     

Massenspektrometrie isomerer Diazaphenanthrene—I

The mass spectra of five diazaphenanthrenes formed by photochemical cyclodehydrogenation of styryl diazines are investigated. It is shown that fragmentation of these compounds starts almost exclusively at the heterocyclic part of the molecule and proceeds by competitive α-cleavage. From the intensity ratios of the ions [M ? H˙]⁺, [M ? HCN]⁺˙, [M ? N₂]⁺˙ and [M ? 2 HCN]⁺˙ generated in this way, each isomer can unequivocally be identified.     

Ion-molecule reactions in the gas phase. part XXII. Reactivity of the cis- and trans-indanediols with dimethyl ether ions

Specific reactivity of cis- and trans-indanediols has been investigated under dimethyl ether (DME) chemical ionization conditions. Several unusual species, such as [M + 29]⁺ and [M + 27]⁺ ions, are produced in high yield. From DME pressure variations and tandem mass spectrometry experiments (low-energy collisions with Ar and NH₃) including some labeled compounds, it appears that [M + 29]⁺ ions are generated by nucleophilic substitution according to a S_Ni pathway from the proton bound[M + DMEH]⁺ adduct ion. On the other hand, [M + 27]⁺ ions are produced from the covalent [M + DME ? H]⁺ adduct ions via a stepwise process inducing a water loss. This latter dehydration occurs from the adducts prepared by [DME ? H]⁺ attachment to the homobenzylic hydroxy site, which allows internal proton transfer from the charged position to the benzylic hydroxy group, promotingthe loss of water. In addition, trans indanediol labeled with ¹⁸O has been used to obtain evidence for the regioselectivity of both water-loss mechanisms from the benzylic site.     

Charge localization and aromatic stabilization in large ring ions: Mass spectra of ms-porphyrins

The major mass spectrometric fragments of ms-tetraphenylporphin and ms-tetra(p-chloro)phenylporphin are [M ? H]⁺˙ and [M ? Cl]⁺˙, respectively. Metal derivatives of these compounds give a modified characteristic fragmentation pattern with peak groups ending in the ions [M ? 4H]⁺˙, [M ? ? ? 5H]⁺˙ and [M ? 2? ? 2H]⁺˙ for the metallo ms-tetraphenylporphins, and [M ? ?Cl ? 2Cl ? 3H]⁺˙ and [M ? 2?Cl ? Cl ? H]⁺˙ for Mgms-tetra(p-chloro)phenylporphin. Deuterated metal derivatives indicate random hydrogen loss from both phenyl and pyrrole carbons. However, metal substituents do not significantly modify the fragmentation pattern in the case of ms-tetra(p-methoxy)phenylporphin. These patterns can be explained in terms of aromatic stabilization of the fragmentation products, coupled with charge localization on the π system in the free base, on the metal atom in the metallo derivatives and on the methoxy function in the p-methoxyphenyl derivative.     

Steric strain and electron-impact. The behaviour of some n,n'-dimethyl-1,1-binaphthyls,some n,n'-dimethylbiphenyls and model compounds

For the title compounds I(M), A[M ? H]⁺ and A[M ? Me]⁺ have been determined. In the biaryl compounds, unlike the xylene and the two dimethylnaphthalenes studied, A[M ? Me]⁺ is noticeably dependent on the position of the methyl group. Deuterium labelling of the methyl groups in the biaryl compounds reveals that more than one process is involved in the formation of the [M ? Me]⁺ ion. In contrast, only in the case of 2,2′-dimethylbiphenyl is the appearance potential of the [M ? H]⁺ ion position dependent. The labelling results suggest complete scrambling of the hydrogen atoms before formation of the [M ? H]⁺ ions. Some comments are made on the problem of trying to relate differences in strain energies and ionisation and appearance potentials in alkyl substituted aromatics.     

Oxidation reactions in triterpenes under chemical ionization conditions

From a collisional activation spectral study it has been found that certain triterpene alcohols with an ursane or oleanane skeleton undergo oxidation to the corresponding ketones under chemical ionization (NH₃) conditions giving rise to abundant [M + NH₄ ? 2]⁺ ions. Mass-analysed ion kinetic energy and B²/E scan results indicate that both [M + NH₄]⁺ and [M + N₂H₇ ? 2]⁺ ions contribute to the formation of the [M + NH₄ ? 2]⁺ ion.     

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.     

Selective reagents in chemical ionization mass spectrometry: Tetramethylsilane with ethers

Chemical ionization mass spectra of several ethers obtained with He/(CH₃)₄Si mixtures as the reagent gases contain abundant [M + 73]⁺ adduct ions which identify the relative molecular mass. For the di-n-alkyl ethers, these [M + 73]⁺ ions are formed by sample ion/sample molecule reactions of the fragment ions, [M + 73 ? C_nH_2n]⁺ and [M + 73 ? 2CnH_2n]⁺. Small amounts of [M + H]⁺ ions are also formed, predominantly by proton transfer reactions of the [M + 73 ? 2CnH_2n]⁺ or [(CH₃)₃SiOH₂]⁺ ions with the ethers. The di-s-alkyl ethers give no [M + 73] ⁺ ions, but do give [M + H]⁺ ions, which allow the determination of the relative molecular mass. These [M + H]⁺ ions result primarily from proton transfer reactions from the dominant fragment ion, [(CH₃)₃SiOH₂]⁺ with the ether. Methyl phenyl ether gives only [M + 73]⁺ adduct ions, by a bimolecular addition of the trimethylsilyl ion to the ether, not by the two-step process found for the di-n-alkyl ethers. Ethyl phenyl ether gives [M + 73]⁺ by both the two-step process and the bimolecular addition. Although the mass spectra of the alkyl etherr are temperature-dependent, the sensitivities of the di-alkyl ethers and ethyl phenyl ether are independent of temperature. However, the sensitivity for methyl phenyl ether decreases significantly with increasing temperature.