Showing papers in "Journal of Mass Spectrometry in 1970"

Analysis of organic salts by laser ionization

Abstract: Alkali salts of 1-hexyl sulfonate were ionized by laser irradiation and the positive ions were analyzed by time-of-flight mass spectrometry. The sodium, potassium, rubidium and cesium salts produce relatively simple spectra. The major organic ions observed are due to the salt plus a cation or the dimer plus a cation. No molecular or fragment ions were detected. The instrumentation and the method of interpreting these data are described.

Kinetic studies in mass spectrometry–VII: Competing cleavage and rearrangement processes in molecular ion decomposition reactions

Abstract: Apparently competing cleavage and rearrangement reactions in a series of molecular ions have been studied by ionization and appearance potential methods, and by determination of the electron energy dependence of both normal and metastable daughter ion peak intensities. The processes investigated were (i) [M CH3] vs. [M CH2O] in anisole; (ii) [M OC6H5] vs. [M CO] in phenyl ether; (iii) [M NO2] vs. [M NO] in nitrobenzene; (iv) [M C3H7] vs. [M C2H4] in butyrophenone: (v) [M C3H7] vs. [M C3H6] in n-butylbenzene; (vi) [M CH2OH] vs. [M CH2O] in 2-phenylethanol; (vii) [M CH3CO2] vs. [M CH2CO] in benzyl acetate; and (viii) [M C4H9O] vs. [M C4H7] in n-butylbenzoate. The results are interpreted in terms of k vs. E curves with very different frequency factors for the two reaction types. Appearance potentials of metastable ions for the rearrangement reactions have also been measured.

Combined gas chromatography-mass spectrometry of the inositol trimethylsilyl ethers and acetate esters

Abstract: Each of the inositol diastereomers have been subjected to low resolution gas chromatography-mass spectrometry as their hexa-O-trimethylsilyl (TMSi) ethers and as their hexaacetyl esters. The TMSi ethers of the inositols each possess a unique spectrum consisting of the same ions occurring with remarkable variation in intensity. This variation, which is much greater with the inositol TMSi ethers than in the spectra of the inositol acetates, is presumably an expression of the stereochemistry of each isomer exaggerated by the bulky TMSi groups. Using TMSi-d9, labeling as well as ring labeling with deuterium we identified several fragment ions which are characteristic of the cyclitols. The spectra of the TMSi inositols are compared with the spectra of other TMSi carbohydrates. Two main series of fragmentation processes are observed in the inositol hexaacetates. With the aid of acetyl-d3 labeling each of these series were found to divide into two more pathways consisting of ions of the same m/e values but of different structures. These pathways are compared with similar pathways observed in other acetyl carbohydrates. A method is described for the direct conversion of TMSi ethers to acetate esters which has potential usefulness in natural product studies.

The ion kinetic energy spectra of some aromatic hydrocarbons

Abstract: The technique of ion kinetic energy spectroscopy has been applied to the study of the aromatic hydrocarbons benzene, toluene, naphthalene, 2-methyl naphthalene, biphenyl and anthracene The method is illustrated by a complete study of naphthalene in which transitions of metastable doubly- and singly-charged ions are listed, including reactions in which singly-charged ions are formed by collision induced charge-exchange reactions of doubly-charged ions and by the double process of charge-exchange and metastable decomposition with loss of one or two hydrogen atoms Decompositions of doubly-charged ions into two singly-charged ions, together with the kinetic energies released in these decompositions, are also given for all the compounds studied

Electron-impact fragmentation of some secondary aliphatic nitramines. Migration of the nitro group in heterocyclic nitramines

Abstract: The mass spectra of a series of nitramines, including the explosives RDX and HMX, are reported. The nature of the major fragment ions is established by labeling with 15N or13C and by high resolution mass spectrometry. Electron-impact-induced fragmentation pathways including the migration of the nitro group in the heterocyclic nitramines, RDX and HMX, are postulated.

Studies in chemical ionization mass spectrometry

Abstract: The relatively minor instrumental modifications necessary to allow the operation of a CEC-21-110B mass spectrometer at pressures as high as 0·5 torr are discussed. The chemical ionization mass spectra of a series of substituted benzophenones have been investigated with several reactant gases: methane, ethane, propane and isobutane. The spectra and behavior of these gases are discussed in general and the specific fragmentation processes of these substituted benzophenones with propane are presented in some detail.

Kinetic studies in mass spectrometry—IX: Competing [M NO2] and [M NO] reactions in substituted nitrobenzenes. Approximate activation energies from ionization and appearance potentials

Abstract: Ionization (IP) and appearance potentials (AP) have been secured for apparently competing [M NO2] cleavage and [M NO] rearrangement reactions in a series of m-and p-X substituted nitrobenzene molecular ions. Approximate activation energies AP–IP were within the experimental reproducibility for most substituents for the [M NO2] reaction of m-and p-X isomer pairs of compounds, but outside it for the [M NO] process. This is interpreted as either effective substituent randomization in the reacting molecular ions or as fortuitously similar activation energies for the [M NO2] cleavage. Assuming the latter, AP–IP for both reactions gave acceptably linear correlations of negative slope when plotted against σ or σ+, which has been interpreted mechanistically in terms of a degree of positive charge dissipation in the rate limiting transition states. These findings are in direct contrast to the energetics of the [M CH3] and [M CH2O] reactions recently studied in substituted anisoles, where plots of AP–IP vs. σ+ displayed positive slopes. The advantages of AP–IP over peak relative abundance as a mechanistic probe are discussed, and corresponding plots of logZ/Z0vs. σ(σ+) and log [A0]/[M0] (1 – f) vs. σ(σ+) for the same reactions are presented and discussed. The disadvantages and limitations of IP and AP measurements are also emphasized.

The decomposition of a triply-charged metastable positive ion of biphenyl

Abstract: The transition, [C12H10]+3[C11H7]+2 + [CH3]+, has been detected both in the ion kinetic energy spectrum and in the mass spectrum of biphenyl. The width of a resulting ‘metastable peak’ has been measured by setting the magnetic field to accept [C11H7]+2 ions and scanning the high voltage at fixed electric sector voltage. The kinetic energy released in the decomposition, calculated from the peak width, amounted to 4.5 eV. With the assumption that this energy release is due entirely to charge separation, the charge distribution in [C12H10]+3 is discussed. The derivation of the equations used to calculate the energy released is given in the Appendix.

Kinetic studies in mass spectrometry—VIII: Competing [M ? CH3] and [M ? CH2O] reactions in substituted anisoles. Approximate activation energies from ioniziation and appearance potentals

Abstract: Ionization and appearance potentials have been determined for apparently competing [M CH3] cleavage and [M CH2O] rearrangement reactions in a series of m- and p-X substituted anisoles. Approximate activation energies AP–IP for most substituents are found not to differ by more than approximately 0.20 eV for m- and p-X compounds with the same substituent. This finding implies either common rearranged molecular ions and/or transition states for the [M CH3] and [M CH2O] reactions; or simply rather similar activation energies in unrearranged molecular ions. Assuming no rearrangment, we have found plots of AP–IP against σ+ to give reasonable linear correlations of positive slope for both reactions. To account for this, it is suggested that in the activated complexes for both cleavage and rearrangement, an additional degree of positive charge is developed at the reaction site, and concordant mechanisms are proposed. These conclusions have been compared to those obtained by application of peak relative intensity methods such as Z-values and their modifications.

The mass spectra of some aliphatic and alicyclic sulphoxides and sulphones

Abstract: Characteristic fragmentation processes of aliphatic sulphoxides and sulphones such as loss of hydroxyl, ‘alkene’ and/or ‘alkenyl’ are associated with hydrogen migrations to oxygen. A study of the mass spectra of di-n-butyl sulphoxide and sulphone, the saturated five-, six- and seven-membered ring sulphoxides and sulphones and their site-specifically deuterated analogues shows that these hydrogen migrations are nonspecific. Apparently steric factors play an important role in determining the relative contributions of initial hydrogen transfer from the various positions. The sites of abstraction probably determine the extent of competition between consecutive or concerted loss of hydroxyl, carbon-sulphur fission or other processes (e.g. McLafferty rearrangement). Apart from the McLafferty rearrangement only the loss of hydroxyl from sulphones shows a strong dependence on the site of initial hydrogen abstraction: γ-hydrogen is lost preferentially, yielding a cyclized [M OH] ion.

Mass spectrometry of piperidine nitroxides—A class of stable free radicals

Abstract: The 2,2,6,6-tetramethylpiperidine nitroxides constitute a family of stable free radicals with electronic structures similar to that of nitric oxide. Ionization of the molecules by electron bombardment does not lead to the formation of a radical-ion, as is the case with even-electron neutral molecules, but instead yields either a biradical or an even-electron molecular ion. The fragmentations of the ions arising from this ionization are described in detail. Accurate mass measurements on most ions (element mapping) and deuterium labelling, where appropriate, have been used to assist in the interpretation of the mass spectra. The observed elimination of nitric oxide from the molecular ions has photochemical analogies.

Mass spectrometry of some pyrrolizidine alkaloids

Abstract: The mass spectra of nine pyrrolizidine alkaloids retronecine, heliotridine, 7-angeloylretronecine, 7-angeloylheliotridine, echimidine, heliosupine, lasiocarpine, heliotrine and echinatine— were studied. Particularly the structures of the ions m/e 214, 197 and 156 in the spectrum of heliotrine are discussed. The ionization and appearance potentials for selected ions were measured for the first six alkaloids, which are pairs of epimers.

Mass spectra of nucleoside derivatives

Abstract: The mass spectra of derivatives of uridine, adenosine, cytidine and guanosine are recorded. Derivatization techniques include permethylation, acetylation, trifluoroacetylation, trimethylsilylation and the synthesis of 2′,3′-O-isopropylidenes and 2′,3′-O-phenylboronic esters. Sequential derivatization by a selective combination of some of these procedures results in nucleosides which are blocked with a characteristic group at the cis 1,2 diol position, and, which contain other substituent groups that enhance the volatility of the compound. The specific substitution at the cis-glycol region has been shown to be particularly useful in asymmetrically derivatizing dinucleoside phosphates since certain fragment ions from their mass spectra indicate the sequence of the two nucleoside components. Sequence isomers such as adenylyl-(3′-5′)-uridine and uridylyl-(3′-5′)-adenosine can be unambiguously distinguished.

Mass spectrometry in structural and stereochemical problems–CXCIV: The mass spectrometric fragmentations of steroidal sapogenins

Abstract: The characteristic mass spectral fragmentation patterns of the basic structure of the steroidal sapogenin, (25R)-5α-spirostan, have been elucidated through the preparation of analogs with deuterium labels at positions 11, 12, 14, 15, 16, 17, 20, 21, 23, 24, 25, 26 and 27. In addition, the effects of a change of stereochemistry at positions 14 and 20, of the introduction of oxygencontaining functionalities mostly in ring F, and of the incorporation of olefinic unsaturation have been determined through synthesis of many examples.

Observations on the mass spectrometry of monensin and related compounds

Abstract: Monensin and nigericin are structurally related compounds belonging to a family of biologically active, polycylic, monocarboxylic acids produced by Streptomyces. Partial interpretation of their mass spectra has been achieved with the aid of high resolution data and by correlation with spectra of derivatives. These results have been applied to structure elucidation of several minor factors produced along with monensin. An interesting aspect of the mass spectrometry of these compounds is that their alkali-metal salts are sufficiently volatile to yield mass spectra. Fragmentation of the salts is markedly different from that of the free acids and their derivatives. A scheme is proposed to account for the formation of a number of fragment ions which contain the metal atom.

Mass spectra of benzotriazoles. Correlation with thermolytic and photolytic fragmentations

Abstract: The mass spectra of some alkyl, aryl and acyl benzotriazoles are reported and discussed on the basis of their thermolytic and photolytic fragmentation products. All benzotriazoles so far studied lose a molecule of nitrogen to give the intermediate radical cations upon electron-impact. Subsequently cyclization and a hydrogen migration lead them to the molecular ions of thermolytic and photolytic fragmentation products. A general rule for predicting the possibility of 1-3 hydrogen migration, based on a knowledge of the electronic state of the radical cation is proposed.

Four‐centred rearrangements in the mass spectra of aliphatic ethers

Abstract: The [CH3OCHCH3]+ ions observed in the mass spectra of ethers of formula CH3OCH (CH3)R(R = H or alkyl) undergo two rearrangement fragmentation reactions to form [C2H5]+ and [CH2OH]+. The scope of the rearrangements has been investigated and it is shown that enlargement of the alkyl group on either side of the ether linkage leads to alternative fragmentation routes. From a study of metastable intensities it is concluded that the fragmentations probably occur directly from the [CH3OCHCH3]+ structure through four centred rearrangements rather than through the intermediacy of the [C2H5OCH2]+ ion.

The mass spectra of some pyrazole compounds

Abstract: 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 chloro-, aminochloro- and ethylaminochloro-s-triazines†

Abstract: The mass spectra of cyanuric chloride and all of the possible amino-and ethylaminochloro-s-triazines have been investigated. The simpler compounds provide evidence for the structures of low mass fragment ions found in the spectra of the more complex derivatives. Fragmentation patterns are presented which account for most of the major ions. These pathways involve either the initial loss of a chlorine atom (important for the simple aminochlorotriazines) or ring cleavage with expulsion of cyanogen chloride (important for cyanuric chloride). The ethyl derivatives undergo cleavage of the side chain prior to either ring cleavage or chlorine expulsion.

The mass spectra of s-triazines

Abstract: The mass spectra of twenty-one s-triazines have been interpreted. An unusual feature noted in the spectra of some of the compounds is transfer of a hydrogen atom of a side chain to a nitrogen atom of the s-triazine ring; two such shifts are suggested as a rationale for the unusual loss of nitrogen from a hydrazide derivative. The fragmentation of triamino- and some diamino- derivatives indicates that imino tautomers play a significant role. The spectra of aryldiamino s-triazines suggest that the site of a substituent in the aryl ring is important in some cases in directing the decomposition; some transitions have been rationalised on the basis of the juxtaposition of the substituent in relation to a nitrogen atom of the heterocyclic ring.

Positive-ion fragmentation mechanisms of some organophosphorus esters

Abstract: The mass spectra of the dimethyl and diethyl esters of phosphonic, phosphorochloridic and phosphorochloridothioic acid have been obtained, and the main paths of decomposition of their positiveions have been compared. Losses of formaldehyde occur from positive ions of all the methyl esters. Losses of C2H3˙ radicals occur consistently from the positive ions of the ethyl esters, but diethyl phosphorochloridothioate differs in showing a principal decomposition path involving initial loss of acetaldehyde. Other details are discussed.

Ortho effects–I: Fragmentation mechanisms in some ortho‐substituted nitroarenes

Abstract: The mass spectra of o-nitrobenzoic acid, o-nitroanisole, o-nitrosobenzoic acid, o-nitrobenzamide, o-nitrobenzyl alcohol and o-nitrosobenzaldehyde have been studied. Fragmentation mechanisms are proposed for the above compounds; their elucidation was aided by isotopic labeling with D and O18. Two ‘ortho-effects’ are discussed; one involving H atom transfer between substituents and the other migration of an atom or group to a charge carrying vacant ortho position. The importance of nitro to nitrite conversion in molecular and fragment ions is discussed.

Kinetic studies in mass spectrometry—IV. The [M — Cl] reaction in substituted chlorobenzenes and the question of molecular ion isomerization.†

Abstract: The [M]+˙ → [M Cl]+ reaction in a series of m- and p-X substituted chlorobenzenes has been studied, utilizing a simple kinetic approach, comparison of metastable ion relative abundances, and by measurement of ionization and appearance potentials. All evidence obtained is consistent with rearrangement prior to cleavage in the molecular ions, in which substituent position becomes effectively randomized. These findings are related to known hydrogen randomization reactions occurring in either the molecular ion or [M Cl] ion of chlorobenzenes. Mechanisms involving carbon scrambling via such species as ionized benzvalenes or prismanes, or ring-opening to isomeric acyclic molecular ions in which hydrogen randomization might occur can be entertained, but mechanisms involving simple hydrogen shifts in the intact benzene ring appear less likely.

The electron-impact-induced fragmentation of 1,2,3-benzotriazoles and some related compounds

Abstract: The mass spectra of 1,2,3-benzotriazole and some derivatives with substituents at the 1-position and in the benzenering have been examined. The loss of N2from the molecularion is characteristic; loss of N2 plus the 1-substituent is also common. Structures are proposed for these fragment ions. The relative ease of loss of N2, NO and NS from the molecular ions of benzotriazole, 2,1,3-benzodiazole, 1,2,3- and 2,1,3-benzothiadiazoles is compared.

Mass spectra of selected beta‐carbolines [β‐9H‐pyrido(3,4‐b)indoles]

Abstract: The mass spectra of fifteen β-carbolines have been interpreted and proposed fragmentations have been substantiated by means of deuterium-labeling and accurate mass determinations. Most decompositions were predictable. An interesting fragmentation was observed in the spectra of 1-alkyl-1,2,3,4-tetrahydro-β-carbolines, which rearrange to expel an alkylamino (RNH) radical from the molecular ion.

Thermal and mass spectrometric fragmentation of esters of deuterated long chain carboxylic acids

Abstract: A method combining thermal fragmentation and mass spectrometry for the determination of the position of double bonds in an unsaturated ester is presented. The thermal fragmentation of methyl esters of deuterated long chain carboxylic acids yields a homologous series of olefins plus a homologous series of unsaturated esters. The positions of the deuterium atoms in the original ester are revealed by the deuterium content of its fragments as determined by mass spectrometry. Therefore, the positions of double bonds of a polyunsaturated acid can be determined by pyrolysis after saturation by deuterium. The structures of the unsaturated fragments are ascertained by mass spectrometric method, and the formation of the ion [M – 32] in the mass spectrometric fragmentation of unsaturated methyl esters is studied by means of deuterium labeling.

Mass spectrometry in structural and stereochemical problems–CLXXXIX: Electron‐impact induced fragmentations and rearrangements of alkoxycyclohexanol trimethylsilyl ethers and alkoxycyclohexyl trimethylsilanes

Abstract: In view of the current interest in the electron-impact induced rearrangements of both trimethylsilyl derivatives and bifunctionalized cyclohexanes, the mass spectral properties of several alkoxycyclohexanol trimethylsilyl ethers and alkoxycyclohexyl trimethylsilanes have been investigated. Using deuterium labeling, the basic fragmentation modes incurred upon electron-impact of ethanol trimethylsilyl ether were elucidated. The major peaks in the spectrum of this simple ether occur also in those of the title compounds, the latter fragments having been formed by interaction of the two functional groups. Thus the initial rearrangement ion of mass 103 (e) from electron bombardment of 4-ethoxycyclohexanol trimethylsilyl ether and 2-ethoxycyclohexyl trimethylsilane corresponds to the [M CH3] ion from ethanol trimethylsilyl ether. Its further fragmentation has been studied using high resolution and metastable ion measurements, and the scope of the interaction between the alkoxy and trimethylsilyl groups, when silicon is attached both to oxygen and to carbon, has been determined. In addition, the origin of every ‘characteristic’ fragment ion has been elucidated on the basis of each corresponding peak in the spectra of several derivatives labeled specifically with deuterium. Peaks derived from initial ionization of both functionalities in each compound have been observed, although the majority of ions in the spectra of both series seem to be directed by fragmentations associated with the trimethylsilyl ether moiety.

The mass spectra of succinimides, hydantoins, oxazolidinediones and other medicinal anti‐epileptic agents

Abstract: The mass spectra of the following common anti-epileptic agents; phensuximide, methsuximide, ethosuximide, ethotoin, mephenytoin, diphenylhydantoin, trimethadione, paramethadione, primidone and phenacemide, have been recorded and interpreted. In addition the mass spectra of succinimide, α-phenylsuccinimide and the N-deuterated derivative of ethotoin were studied. The investigated compounds fragment in an interesting manner and give rise to stable ions by which means they are readily identified. The most diagnostic fragmentation in the majority of the spectra was the expulsion of a (CO)2NR fragment from the molecular ion.

Metastable ion fragmentation processes in n-alkanes

Abstract: The n-alkanes, propane to heptane, have been studied in a modified MS-9 mass spectrometer under conditions that enabled the daughter ions, resulting from metastable fragmentation processes occurring in the first field free region, to be observed with high sensitivity. The precursor ions in these fragmentations have been identified unambiguously and a general fragmentation scheme for the n-alkanes is proposed. The mass spectrometer incorporated a variable width monitor slit and narrow settings of this slit improved the energy resolution so that fine structure could be observed in some of the ‘metastable peaks’. The implications of this fine structure are discussed.

Reactions of aliphatic aldehydes under electron-impact†

Abstract: The mass spectra of hexanal, heptanal and nonanal variously labeled with deuterium confirm γ-hydrogen migration and β cleavage as the mechanism leading to [C2H4O]+˙ and [M C2H4O]+˙, although the data on the latter are complicated by contributions from other, related paths. In addition, they show that three other major primary decomposition products, [M C2H4]+˙, [M H2O]+˙ and [C3H5O]+, all arise in large part by processes involving γ-hydrogen migration to the oxygen atom. The ethylene lost to yield the first of these products consists of the α and β methylene groups. The loss of ethylene most likely occurs by way of a cyclobutanol intermediate, which, via alternative reaction paths, may well contribute to the yields of the other two products as well. These findings further extend the range of parallelism between photochemical and electron-impact-induced reactions.