Showing papers in "Journal of Mass Spectrometry in 1968"

Gas chromatographic—mass spectrometric studies of long chain hydroxy acids.—III.1 The mass spectra of the methyl esters trimethylsilyl ethers of aliphatic hydroxy acids. A facile method of double bond location

Abstract: Trimethylsilylation has proved to be extremely useful in the gas chromatography and the mass spectrometry of hydroxy acid methyl esters. The characteristic mass spectral fragmentation patterns have shown these derivatives to be superior in some respects to others for structural elucidation; in particular, hydroxylation followed by trimethylsilylation provides a useful method of double bond location in unsaturated fatty acid esters.1

Stereoisomeric effects on mass spectra—I. A Review

Abstract: The unimolecular reactions that give rise to mass spectra are controlled by spatial relationships and energy considerations. In molecules that contain a heteroatom, elimination reactions, involving bond-making as well as breaking, are often prominent, e.g. loss of water from alcohols. The ease of such reactions depends on spatial relationships in the molecule, and the resultant ion intensities in the spectra of geometric isomers can consequently be correlated with differences in geometry and hence furnish a basis for assigning structures. Processes that do not involve bond-making do not have such rigorous geometric requirements, but depend rather on attainment of a transition state defined in terms of a minimum energy content. Common product ions from stereoisomeric hydrocarbons seem often to arise via a common transition state. When this condition holds, the difference between the enthalpies of the isomers is reflected in the relative appearance potentials and–though the cause-and-effect relationship here is less direct and more readily obscured by other factors–relative intensities of the common product derived from the isomers. In both classes of processes, the spectra of stereoisomers can be simplified and made more distinctive by lowering source temperature and ionizing voltage.

Electron impact‐induced rearrangement of trimethylsilyl groups in long chain compounds

Abstract: Mass spectra of trimethylsilyl (TMS) derivatives of long chain dicarboxylic acids, hydroxy acids, cyano acids, and terminal diols, dithiols and diamines have been examined. A number of fragmentation pathways involving rearrangement of partial or intact TMS groups between the termini or remote points in the chain have been determined, using deuterium and carbon-13 labeling, and high resolution mass spectrometry. Knowledge of the occurrence of functional group migrations of this type is essential to the correct interpretation of mass spectra of TMS derivatives, which are now in wide use in mass spectrometry and gas chromatography. These data in addition provide further evidence for the general ability of remote functional groups to interact, by winding or coiling of long chains. A number of interesting doubly-charged ions are reported, in which the charges are reported, in which the charges are located at opposite ends of long chains, and for which no singly-charged counterparts are observed.

Zur Massenspektrometrie von Nitrophenylverbindungen—I. Nitrophenylphydrazone Aromatischer Aldehyde und Ketone und Verweandte Verbindungen

Abstract: Die Fragmentierung von Nitrophenylhydrazonen aromatischer Aldehyde und Ketone, von Nitrostillbenen, Nitrobenzalacetophenonen und analogen Verbindungen unter Elektronenbeschuss wird entscheidend durch intramolekulare Oxidationsreaktionen beeinflusst, sofern sich eine Nitrogruppe in o-Stellung zum ungesattigten substituenten befindet. Es findet eine Sauerstoffubertragung von der o-Nitrogruppe auf die Hydrazon- oder Stilbendoppelbindung statt; ein wesentlicher Teil der charakterisierenden Fragmente in den Massenspektren dieser Verbindungen stammt aus dem Zerfall dieser Sauerstoffubertragungsprodukte. 20 Spektren von 40 untersuchten Verbindungen werden prasentiert und diskutiert. Eine Reihe weiterer umlagerungsreaktionen werden beobahtet. Eine konjugierte zusatzliche Dopplbindung in der Hydrazonkette andert die Reaktivitat der Verbindung vollsandig. auch die Fragmentierung gesattigter Substituenten (Cyclopropyl) kann durch eine o-Nitrogruppe entscheidend beeinflusst werden. Fragmentation under electron impact of phenylhydrazones of aromatic aldehydes and ketones, of nitrostilbenes, nitrobenzalacetophenones and analogous compounds is determined by intramolecular oxidation reactions. Oxygen transfer from the o-nitrogroup on to the hydrazon- or stilbene-double bond is taking place; degradation of the resulting rearrangement products provides some of the most characteristic features in the mass spectra of such compounds. The spectra of 20 out of 40 compounds investigated are presented and discussed. Several other rearrangement reactions are observed. An additional conjugated double bond in the hydrazone chain completely changes the reactivity under electron impact. Even saturated substituents (cyclopropyl) can be drastically affected in their mode of fragmentation by an o-substituted nitrogroup.

High resolution mass spectrometry.—II Some substituted benzothiazoles

Abstract: The mass spectra of nineteen substituted benzothiazoles have been recorded and the identity of the various ions in the mass spectra has been established by high resulution (accurate) mass measurement. Deuterium labelling has been used to elucidate the fragmentation processes of these compounds. The parent compound of the series, benzothiazole, exhibits the loss of hydrogen cyanide and carbon monosulphide from the parent ion as the most important decomposition pathways. The hydrogen atom concerned in the loss of hydrogen cyanide is shown to originate from the 2-position of benzothiazole, while in 2-substituted benzothiazoles, different mechanisms are apparent for the loss of hydrogen cyanide, and these are clarified by deuterium labelling. Some substituted benzothiazoles can lose sulphur from their molecular ions, a process which does not occur in benzothiazole itself. The substituted benzothiazoles undergo many other types of fragmentations, in some cases retaining the substituent, and in other cases losing it prior to collapse of the thiazole ring.

The mass spectra of some chlorinated pesticidal compounds

Abstract: The mass spectra of nine bridged polycyclic chlorinated pesticidal compounds have been investigated, and fragmentation modes to account for the more abundant ions are postulated. The principal features of the spectra are ions corresponding to a set of retro-Diels-Alder decompositions, ions resulting from successive losses of Cl, HCl, or both, ions produced by combinations of a retro-Diels-Alder process with a preliminary or subsequent loss of Cl or HCl, and ions whose processes of formation more specifically involve the epoxide group.

The mass spectra of some alkyl and aryl oxazoles

Abstract: The mass spectra of a variety of alkyl and aryl oxazoles have been determined and the spectra analyzed with the aid of deuterium labelling and high resolution mass spectrometry. In contrast to the corresponding benzenoid compounds, the mass spectra of isomeric alkyl oxazoles are distinctive and in this respect are akin to those of the corresponding pyridines. Further analogy to the pyridines is suggested by the unfavorable nature of a carbonium ion adjacent to the 2-position and this effect may be used to locate alkyl substituents attached to the oxazole nucleus. The loss of carbon monoxide from the molecular ions of 2,5-disubstituted oxazoles probably occurs with ring opening and migration of the C-5 substituent (e.g.Br) to the C-4 position.

Einfluss funktioneller Gruppen auf die Massenspektren von 17β-Hydroxysteroiden

Abstract: AM Beispiel des 17β-Hydroxy-5α-androstans wird der unterschiedliche Einflus funktioneller Gruppen auf die Bruchstuckbildung von Steroiden studiert. Im 17β-Hydroxy-5α-androstan wird durch die Hydroxylgruppe lediglich die in Steroiden vorhandene eigung zur Spaltung der C-13/C-17 Bindung unter Ausbildung eines positiven Ladungszentrums an C-13 vertarkt. Dieser Einflus der Hydroxylgruppe uberwiegt aber nur, solange Substituenten fehlen, die zur Ionisation einen geringeren Energieaufwand benotigen, als zur Ionisation der C-13/C-17 Bindung erforderlich ist. Bereits bei Vorhandensein einer Doppelbindung kann sich das Spaltbild stark wandeln. Wenn sich aber in Stellung 17 noch eine zusatzliche Alkygruppe befindet, so erfolgt die Ionisation mit hoher Wahrscheinlichkeit durch Abspaltung eines Elektrons vom Hydroxylsauerstoff in Stellung 17. Es treten daher andere Hauptabbaureaktionen ein als in Molekulionen, die das Ladungszentrum am C-13 haben. In solchen Verbindungen ist selbst der dominierende Einflus eines konjugierten Systems auf die Bruchstuckbildung weitgehend eingeschrankt. Bei Veratherung der Hydroxylgruppe wird dieser Effekt potenziert. Im Zuge dieser UNtersuchungen wurden einige bisher noch nicht bekannte, fur die Anwesenheit bestimmter Strukturelemente im Steroidskelett typische Abbaureaktionen aufgefunden, die ebenfalls kurz diskutiert werden. The different influence of functional groups on fragmentation reactions is demonstrated by the example of 17β-hydroxy-5α-androstanes. In 17β-hydroxy-5α-androstane the tendency of steroids to be cleaved by rupture of the C-13/C-17 bond under production of a charged centre at C-13 is only enhanced by the hydroxyl group. This influence of the hydroxyl group only predominates as long as substituents are absent which need less energy for ionization than is necessary to ionize the C-13/C-17 bond. Even the presence of a double bond may change the fragmentation pattern completely. If, however, an additional alkyl group is located at C-17, ionization occurs with high probability by elimination of an electron from the OH group connected to C-17. Therefore, other main degradation reactions occur than in molecular ions, having the charge located at C-13. In such compounds even the dominant influence of a conjugated system on the fragmentation reactions is considerably reduced. By etherfication of the hydroxyl group this effect is still very much increased. In the course of this investigation some not yet known degradation reactions, rather typical for the presence of certain groups in the steroid skeleton, were found. These are discussed briefly.

Massenspektren Schwach Angeregter Moleküle. 4.Mitteilung

Abstract: Die thermische Anregungsenergie der Molekule beeinflust mehrstufige Abbaureaktionen aliphatischer Verbindungen im massenspektrometer sehr stark. Thermische Anregung erhalten die Molekule vielfach erst durch Wandstose in der Ionenquelle. Da in den Wenigsten Fallen die Ionenquellentemperature vollig konstant gehalten werden kann, unterscheiden sich Spektren ein und derselben Verbindung oft in ihren Intensitatwerten voneinander. Diesem Umstand sollte bei der Anlage von Spektrensammlungen Rechnung getragen werden. Durch Erniedrigung von Elektronenenergie und Ionenquellentemperatur lassen sich mehrstufige Abbaureaktionen os lenken, das vorzugsweise nur primare Spaltprodukte entstehen. Die Spektren werden dadurch qualitativ besser auswertbar. Bie Anwendung dieses Verfahrens auf bifunktionelle aliphatische Verbindungen Konnen nahezu samtliche Spaltstucke ovn Molekulionenspezies abgeleitet werden, die an der einen oder anderen funktionellen Gruppe ionisiert wurden. Je nach der Mange der durch Ionisation an einer der Gruppen entstandenen Fragmente kann man daher den Einflus der Substituenten miteinander vergleichen und diese nach steigender Einflusnahme auf die Bruchstuckbildung in einer Reihen anordnen. Es ergibt sich danach etwa die folgende Reihung: The thermal excitation energy of molecules greatly influences multistep degradation reactions of aliphatic compounds in the mass spectrometer. Molecules very often obtain their thermal excitation energy only within the ion source by wall collisions. Since it is not usually possible to keep the ion source temperature entirely constant the peak intensities in the spectra of one and the same compound differ considerably. Attention should be paid to this fact in the preparation of mass spectra collections. Multistep degradation reactions may be influenced by reduction of the electron energy and the ion source temperature such that only primary degradation products are preferentially formed. The interpretation of such spectra is easier. This technique was used to study the fragmentation reactions of bi-functional aliphatic compounds. It was shown that nearly all fragments can be deduced from molecular ion species, ionized at one or other functional group. Depending on the amount of fragments produced by ionization at the functional group it is possible to compare the iniluence of the various substituents on the fragmentation, and to rank them according to their increasing influence on the fragmentation as shown:

The primary fragmentation step of isoxazole upon electron impact. A correlation with photochemistry

Abstract: Three isomeric compounds, I, II and III, were prepared and their mass spectra recorded. Comparisons of the spectra showed that the fragmentation of I proceeds only by way of II, and that II itself is transformed in part to III upon electron impact. It is suggested that selective ionization of each one of the two isolated functional groups in II may afford two isomeric radical ions, IIa and IIb. A possible interrelation to the photochemistry of these compounds is also discussed.

Skeletal rearrangements in mass spectra. Part I. Bis-aryl compounds

Abstract: Examination of a large number of spectra indicates that bis-unsaturated compounds commonly undergo a skeletal rearrangement in which part or all or the bridging moiety is eliminated, often with concomitant loss of hydrogen atoms. The spectra of labeled azobenzene, diphenyl sulfide, and their p,p′-dimethyl derivatives show that scrambling of hydrogen atoms precedes or accompanies such rearrangements, in contrast to the loss of a p-methyl group from the latter derivatives. These results are rationalized in terms of the radical site formed on one unsaturated functional group attacking the polarizable π-electrons of the other unsaturated group.

The mass spectra of metal complexes of dibenzoylmethane

Abstract: The mass spectra of a series of metal complexes of dibenzoylmethane have been rationalized. The paths of novel rearrangement reactions involving both hydrogen and oxygen migration may differ according to the type of metal atom in the complex. Further examples are proposed of the effect of metal valency changes in ion reactions.

A study of rearrangement processes in the mass spectra of substituted benzophenones which provide a guide to orientation

Abstract: An investigation of the mass spectra of substituted benzophenones has shown that a number of rearrangement processes are operative. The rearrangements have been shown to involve solely the ortho-substituents to the carbonyl group and in many cases the carbonyl oxygen atom itself participates in the processes. Deuterium labelling experiments combined with data obtained from accurate mass and metastable analysis have enabled the probable mechanisms of rearrangement and fragmentation to be elucidated. An understanding of these processes should greatly assist in the location of substituents in unknown benzophenones.

Mass spectrometry and organic analysis—XII αβ-Unsaturated secondary alcohols†

Abstract: The fact that some αβ-unsaturated alcohols give mass spectra that bear some similarity with the corresponding saturated ketones is discussed, and the double hydrogen transfer necessary to accommodate this is examined by deuterium labelling.

Energetics of the electron-impact fragmentation of alkoxybenzenes and alkylthiobenzenes

Abstract: Using energetic considerations, ketonic structures are postulated for the [Molefin]+ fragments derived from alkoxybenzenes, alkylthiobenzenes and 9-ethoxyanthracene. Experimentally determined heats of formation for the tautomeric molecular ions derived from anthrone and 9-anthrol differ by 37 Kcal. mole−1.

A study of rearrangement processes in the mass spectra of substituted diphenyl‐ethers

Abstract: An investigation of the mass spectra of a number of substituted diphenyl ethers has shown that the major fragment ions are commonly due to cleavage of the molecule into the two benzene ‘half’ fragments although in many cases the molecular ion is the most abundant species observed. Little evidence is seen of MCO or MCHO peaks in these molecules but a large number of different rearrangement processes have been observed which involve ortho-substituents. These rearrangement ions, although in some cases not very abundant, can be diagnostic in the problem of locating substituents in the diphenyl ether nucleus.

Mass spectometry of aralkyl compounds with a functional group—VI1: Mass spectra of 1-phenylethyanol-1, 2-phenylethanol-1 and 1-phenylpropanol-2†

Abstract: Mass spectra of 1-phenylethanol-1 and its analogues, specifically deuterated in the aliphatic chain, suggest that the [MCH3]+ ion is represented partly by an α-hydroxybenzyl fragment. Moreover, the molecular ion loses successively—after scrambling of all hydrogen atoms, except those of CH3a hydrogen atom and C6H6, generation the CH3CO+ ion. Diffuse peaks, found in the spectra of of 2-phenylethanol-1 and its analogues, specifically deuterated in the aliphatic chain and in the phenyl ring, show that the molecular ion loses C2H4O, possibly via a four-center mechanism, after an exchange of aromatic and hydroxylic hydrogens. Mass spectra of 1-phenylpropanol-2 and its analogues, specifically, deuterated in the aliphatic chain, demonstrate that in the molecular ion exclusively the hydroxyl hydrogen atom is transferred to one of the ortho-positions of the phenyl ring via a McLafferty rearrangement, generating the [M C2H4O]+ ion. Furtherore, an eight-membered ring structure is proposed for the [M CH3]+ ion to explain the loss of H2O and C2H2O from this ion after an extensive scrambling of hydrogen atoms.

The mass spectra of some guanidines

Abstract: The mass spectra of guanidine and ten of its derivatives have been studied under both high and low resolution conditions. Evidence was detected for the migration of methyl groups, the formation of intermediate three-membered ring structures and decompositions involving expulsion of N. with release of kinetic energy.

Fragmentations in the mass spectra of 2‐oxo‐3‐indolyl derivatives

Abstract: The mass spectra of a series of isatin, oxindole and 2-oxo-3-indolyl derivatives have been investigated using high resolution and deuterium labelling techniques. The fragmentations involve the sequential loss of a number of neutral molecules and the results show that the concept of charge localisation can be applied with success to explain the fragmentation processes even in these polyheteroatom species.

The oxygen rearrangement of aromatic and unsaturated esters under electron‐impact—I: General regularities of the rearrangement

Abstract: Some esters of γ, δ-unsaturated or β-arylsubstituted acids undergo a peculiar transformation under electron-impact including an elimination of the alcohol residue as a radical R. with the following loss of the ketene molecule. One of the oxygen atoms of the carbonyl group enters an ion which is formed from an unsaturated part of the molecule. The possible mechanism of this reaction and the influence of structural modifications on the course of this process are discussed.

Mass spectra of azetidines and 2-azetidinones†

Abstract: The mass spectra of twenty three azetidines and seventeen 2-azetidinones are reported and discussed. The majority of spectra contain molecular ions. Fragmentation modes are largely dependent upon the substitution pattern and involve specific cleavage of the four-membered ring. Several hydrogen rearrangement reactions occur, and in some cases, cis and trans isomers may be distinguished by large differences in the relative abundances of certain fragment ions.

High resolution mass spectrometry in molecular studies. Part XVII. Evidence for ring contractions in molecular ions: The fragmentation of N‐acetylmorpholine

Abstract: In comparing N-acetylmorpholine to closely related systems, two major differences in fragmentation are observed M-15 and M-43 fragments, although quite common to such systems, are unusual with respect to their genesis Formation of the M-15 fragment by loss of C-3 instead of the anticipitated loss of C-2 or C-8 is evident from shifts in the spectra of deuterated analogs The M-43 species arises from total loss of the N-acyl substituent rather than the usual two-step loss of ketene plus a ring hydrogen These data are presented in support of mechanistic rationale involving radical induced ring contraction to a common intermediate molecular ion Techniques of high resolution mass spectrometry and isotope labeling have been employed to substantiate certain mechanistic details

Massenspektren von sekundären Vinylcarbinolen

Abstract: Die Massenspektren sekundarer des Typs RCH(OH)CHCH2 zeigen die gleichen Bruchstucke wie die der isomeren Athylketone RCOC2H5. Dies ist auf eine Umlagerung der Molekulionen der Vinylcarbinole in solche der Athylktone vor Eintritt der Bruchstuckbildung zuruckzufuhren. Die Massenspektren beider Verbindungsklassen unterscheiden sich nur geringfugig in den Intensitatswerten. The mass spectra of secondary vinylcarbinols of the structure RCH(OH)CHCH2 show the same fragments as those of the isomeric ethylketones RCOC2H5. 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.

The mass spectra of some cyclic ethers

Abstract: The mass spectral fragmentations of the saturated five-, six- and seven-membered ring ethers have been determined by studying their site-specifically deuterated analogues by both high and low-resolution mass spectrometry. The initial processes, governing the fragmentations of the cyclic ethers are shown to be identical with the well-known processes of linear nonbranched ethers, i.e. predominant α-fisson in the lower members and predominant carbon-oxygen fisson with charge retention on the carbon atom in the higher members.

‘Mass spectrometry of vitamin B6: Different forms of the vitamin, its metabolites, antimetabolites, and analogs’

Abstract: The mass spectra of the different forms of vitamin B6, some metabolites and antimetabolites, and some analogs are reported. The free bases are suitable for study, but the 5-phosphates are not sufficiently volatile. The hydrochloride salts dissociate thermally in the inlet system into the free base and HCl and give the spectrum of the free base with the spectrum of HCL superimposed on it. The compounds studied are: pyridoxol, pyridoxamine and pyridoxal, which are different forms of vitamin B6; 4-pyridoxic acid and its lactone, 5-pyridoxic acid lactone, isopyridoxal, 5-formyl-3-hydroxy-2-methylpyridine-4-carboxylic acid, and 3-hydroxy-2-methylpyridine-4,5-dicarboxylic acid, which are vitamin B6 metabolites; α4-and α5-deoxypyridoxol, 3-deoxypyridoxol, and 4- and 5- norpyridoxol, which are antimetabolites and analogs of vitamin B6.

High resolution mass spectrometry—I. Some substituted δ‐lactones

Abstract: The mass spectra of some δ-lactones substituted in various positions by methyl groups have been studied both by accurate mass measurements at high resulution and by deuterium labelling. The loss of carbon dioxide has been shown to be important only for a mono-substituted lactone. A fragmentation mode common to all the lactones studied is the elimination of the ring oxygen atom, plus the adjacent carbon atom with its substituents, as a neutral carbonyl molecule such as formaldehyde, acetaldehyde or acetone. Deuterium labelling has uncovered the existence of a rearrangement involving hydrogen transfer in an even-electron ion, and a mechanism involving a six-membered transition state is proposed for this. The bond fissions, common to all the lactones, by which the principal ions in the mass spectra arise, are summarised.

The mass spectrum of 1‐(2‐thienyl) hexane‐1‐13C

Abstract: The mass spectrum of 1-(2-thienyl) hexane-1-13C is reported. The principal fragmentation routes ofthe parent ion are delineated. Beta cleavage of the alkyl chain predominates, and the label retention indicates that the alpha carbon atom remains with the charged ring moiety. A substantial part of the m/e 97 ion undergoes a ring expansion to a six membered ring. A small amount of alpha cleavage of the alkyl chain occurs with the expected loss of the label. Further fragmentation of the ions from initial alpha or beta cleavage produces similar fragment ions. It is noted that many of the neutral particles lost in the formation of the fragment ions are typical of those encountered in the alkylbenzenes or other aromatic ion systems.

The fragmentation of organic molecules under electron-IMPACT—II. The mass spectra of tetronic acid and some of its derivatives†

Abstract: The mass spectra of tetronic acid and of a number of its derivatives are recorded and discussed. Where necessary, the composition of the fragment ions has been checked by high resolution mass measurements. Fragmentation of the molecular ion is explained in terms of the rupture of a bond attached to C-4, and the predominant routes for many of the compounds can be explained on the basis of two schemes, the first involving preliminary ketonisation of the molecular ion, followed by elimination of carbon monoxide, the second involving rupture of the C-4R3 bond prior to elimination of carbon monoxide. Special structural features, however, provide alternative routes.

Etude Des Spectres de Masse Des Constituants Amers Des Simarubacées

Abstract: The bitter compounds isolated from the species Simaroubaceae represent a new family of degraded triterpenoids. Ailanthone, glaucarubolone and chaparrinone having a C20 skeleton belong to this family and their structures were previously determined. Mass spectra of these compounds and some of their derivatives have now been studied in detail and the results obtained are discussed in this communication. The observed fragmentation pattern is characteristic of the structural features of this group of compounds.