Mass spectra of germacranolide type sesquiterpene dilactones and derivatives

The low and high resolution mass spectra of five germacranolide sesquiterpene dilactones together with the d₀-, d₃-acetates, d₀-, d₉-TMSi derivatives and deuterium exchange products were obtained. The mass spectra of the five dilactones revealed several kinds of common fragment ions. The germacranolides containing a 4,5 double bond exhibit characteristic ions at m/e 274, 256, 228, 165 and 147, while the 4,5-dihydro compound exhibits fragment ions at m/e 276, 258, 230 and 162.     

Mass spectra of alkylferrocenes and biferrocenyls

Mass spectra of alkylferrocenes and biferrocenyls have molecular ion peaks which are also base peaks. The predominant fragment ions are formed by beta-cleavage of the alkyl group. Gamma-and alpha-cleavages are the only other significant modes of alkyl side-chain fragmentation. The cleavage of the alkyl group is often accompanied or followed by the cleavage of either one or both of the cyclopentadienyl-iron bonds. Weak m/e 121 ([C₅H₅]⁺) mass peaks are found in the spectra of 1,1′-dialkyl- and 1,1′-disilyl-ferrocenes. Therefore, the m/e 121 peak may not be used as a sensitive criterion to determine the presence of unsubstituted cyclopentadienyl rings. The relative intensity of the peak may, however, serve as an indicator. Expansion of the cyclopentadienyl ring to six- and seven-carbon rings in the fragmentation of alkylferrocenes, diethylbiferrocenyl and deuterated ethylferrocenes is indicated. The spectra of benzylferrocene and benzylferrocene-alpha-d₂ do not show a beta-cleavage but suggest a pentalene ring formation. Methyl and phenyl groups in the beta-position of substituted ferrocenes were found to migrate to the iron atom.     

Mass spectral studies on steroidal compounds. VIII—a comparative study of 6- and 7-oxalactones

The mass spectra of three steroidal ring B 7-oxalactones and one 6-oxalactone have been examined and comparison made with previously studied spectra of 6-oxa isomers. Whereas the mass spectra of 6-oxalactones are conspicuous by an intense peak at m/e 318, no such peak was found for 7-oxalactones. On the contrary, the 7-oxalactones showed characteristic [M ? CH₂O]⁺ ions. Thus, mass spectrometry offers an excellent means of differentiating between isomeric 6- and 7-oxa ?-lactones in the cholestane and β-sitostane series. The fragmentation pathways suggested are supported by accurate mass measurement of some of the salient fragment ions.     

Structure of chlorinated poly(vinyl chloride). III. Preparation of poly(vinyl chloride)-β,β-d2 as a model for the study of the mechanism of chlorination and of the chlorinated poly(vinyl chloride) structure

A method for the preparation of poly(vinyl chloride)-β,β-d₂ (PVC-β,β-d ₂) as a model for the investigation of the mechanism of chlorination and of the CPVC structure has been suggested. The conditions of preparation of deuterated intermediates of a multistage synthesis of vinyl chloride-β,β-d₂ and of suspension-polymerized PVC-β,β-d₂ have been described including the mass balance. Malonic acid was used as the starting compound. Tacticity values of a sample of PVC-β,β-d₂ and its infrared and NMR spectra are presented and compared with data already published.     

Structure of chlorinated poly(vinyl chloride). IV. Chlorination of β,β-d2-poly(vinyl chloride) as model for determination of the mechanism of chlorination

Chlorinated β,β-dideuterated poly(vinyl chloride) (β,β-d₂-CPVC) was prepared by photochemical suspension chlorination in concentrated hydrochloric acid with chloroform as swelling agent, and thermally in tetrachloroethane solution. ¹H-NMR (nuclear magnetic resonance) spectra of β,β-d₂-CPVC were recorded. The content of deuterium was determined in combustion products of β,β-d₂-CPVC as the D₂O:(H₁D)₂O ratio by means of mass spectroscopy. Both in the photochemical suspension chlorination and in the thermal solution chlorination of β,β-d₂-PVC, a decrease of the concentration of ? CHCl? groups was observed. The differences in structure of the suspension chlorinated and solution chlorinated β,β-d₂-PVC were confirmed.     

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

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.     

Stereochemical studies by mass spectrometry: C15Nuphar alkaloids

Representative C₁₅ Nuphar alkaloids, containing the quinolizidine system, were studied by high-resolution mass spectrometry and metastable-ion decomposition analysis. The appearance with N-oxide species of ions at m/z 168, useful in ascertaining the stereochemistry of the quinolizidinic ring junction, are also discussed.     

A field ionization study of octan-2-one

H/D randomization is not observed within the octan-2-one-1,1,1,3,3-d₅ molecular ion at times less than 7 × 10^?10 sec following field ionization. Partial H/D randomization is observbed at 10^?6 to 10^?5 sec. It is deduced that the curves of microscopic rate constant k against internal excitation energy E for the reactions effecting randomization and for the McLafferty rearrangement intersect. The field ionization kinetics (FIK) for the McLafferty rearrangement in octan-2-one-1,1,1,3,3-d₅ are investigated over a time range extending from 10^?11 to 10^?6 sec. The maximum microscopic rate constant k for the reaction is estimated as 5 × 10¹⁰ sec^?1. It is suggested that FIK measurements with a double focusing mass spectrometer be made by sweeping the blade potential rather than by the alternative technique of sweeping the electric sector analyzer potential. The ‘normnal’ FI mass spectra of octan-2 one and octan-2-one and octan-2-one-1,1,1,3,3-d₅ are presented and discussed. It is proposed that the m/e 56 species in the ‘normal’ FI mass spectrum of octan-2-one represents a doubly charged ion formed by loss of oxygen in a surface process.     

Die massenspektrometrische Identifizierung von Alkyl-1, 3-thiazolen

Positional isomers of mono-, di- and trialkyl-1,3-thiazoles can be identified unequivocally by their electron impact mass spectra and differentiated from their isomers. The decisive criteria for this are the m/e values and the relative abundances of significant ions, in particular of the molecular ions, the [M – 1]⁺ ions, the thiazolylmethyl carbocations or their ring expanded thiazinium structures, and also of the thiiren radical ions which are formed upon the elimination of a nitrile molecule with ring contraction. In this way, 22 thiazole derivatives have been identified in the glass capillary gas chromatogram of aroma constituents of roasted coffee using a gas chromatograph mass spectrometer system. The structural correlations are substantiated by comparative measurements with a series of authentic samples.     

The reaction intermediate spectrum. A new type of experiment in tandem mass spectrometry

A new scan is described which responds to ions that are intermediates in the dissociation of a mass-selected parent ion (m_p) to give a mass-selected daughter ion (m_d). The scan gives a simple mass v. abundance output for ions which satisfy this condition. It is implemented here on a BEQQ hybrid mass spectrometer using, in sequence, collision-induced dissociation occurring at high energy in the first reaction region, and low-energy collisional activation in the collision quadrupole. The experiment provides information on reaction sequences not available from single scans of other types. In the several cases examined, it is demonstrated that, among many conceivable fragmentation routes connecting a parent ion with a particular fragment ion, only a few are significant. Examination of reaction intermediate spectra also appears to be a fruitful new approach to mechanistic questions, as illustrated by consideration of the behavior of several isomeric octanones. These new spectra also have analytical value: they show good signal-to-noise ratios and allow ready distinction between isobaric and isomeric ions. A comparison of the reaction intermediate spectrum with a daughter spectrum obtained by the B/E linked-scanning technique reveals the contributions of artifact peaks which result from poor parent ion mass resolution in the latter. Reaction intermediate spectra combine information from the daughter spectra of m_p and the parent spectra of m_d and, as a specified portion of this data domain, have unique characteristics.     

Ion cyclotron resonance mass spectrometric study of ion—molecule reactions in toluene—pyridine mixtures

Ion—molecule reactions in toluene, toluene-d₈, pyridine, 4-methyl-, 4-ethyl- and 4-terr-butylpyridine and quinoline and their mixtures were studied by ICR mass spectrometry at 10^-7 Torr (1 Torr = 133.3 Pa). The reactions of benzyl (m/z 91), benzyl-d₇ (m/z 98), methylbenzyl (m/z 105), and azabenzyl (m/z 92) ions with pyridines and quinoline were observed. The reactions of protonated pyridines with unprotonated molecules leading to homoconjugated ions (BHB)⁺ were detected.     

Zur Lokalisierung funktioneller Gruppen mit Hilfe der Massenspektrometrie. XVII—Massenspektren von 3,6,20β-Trihydroxy-pregnanen

Mass spectra of 3,6,20β-trihydroxypregnanes differ greatly, depending upon the nature of the A/B ring fusion and the positions of the hydroxy groups. Of all the isomers only 3α,6β,20β-trihydroxy-5β-pregnane produces an intense, structurally significant, ion at m/e 263. For 3β,6α,20β-trihydroxy-5α-pregnane an ion of m/e 141 is typical.     

Mass spectrometric analysis of N-substituted cyclohexene-1,2-dicarboximides

Both low and high resolution mass spectra of cis-4-cyclohexene-1,2-dicarboximide, its N-methyl, N-ethyl, N-n-propyl and N-n-butyl derivatives, and cyclohexane-1,2-dicarboximide were obtained at 70 eV. Each of the spectra exhibited characteristic nominal ions at masses 151, 136, 123 and a group of ions at masses 77, 78, 79, 80 and 81 of which m/e 80 was always the base peak except for the unsubstituted cyclohexane compound. The m/e 77 to 81 fragments are composed of carbon and hydrogen and derived from the cyclohexene ring. The ions possessing higher masses are heterocyclic and certain of them show doublets and triplets. Evidence for a 1,3 hydrogen migration was supplied by studies with the N-(ethyl-2-d₃) derivative and evidence for a 1,4 migration by the N-(n-propyl-3-d₃) derivative.     

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

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.     

Stereoregularity of poly(2-vinylpyridine) and poly-(4-vinylpyridine)

In order to determine the stereoregularity of poly(4-vinylpyridine), 4-vinylpyridine-β,β-d₂ was synthesized from 4-acetylpyridine. The ¹H-NMR spectra of the deuterated and nondeuterated polymers were measured and analyzed. From the ¹H-NMR spectra of poly(4-vinylpyridine-β,β-d₂), triad tacticity can be obtained, while the ¹H-NMR spectra of nondeuterated poly(4-vinylpyridine) give the fraction of isotactic triad. The ¹³C-NMR spectra of poly(4-vinylpyridine) were also observed, and the spectra of C₄ carbon of polymers were assigned by the pentad tacticities. The fraction of isotactic triad of poly(2-vinylpyridine) and poly(4-vinylpyridine) obtained under various polymerization conditions were determined. The radical polymerization and anionic polymerizations with phenylmagnesium bromide and n-butyllithium as catalysts of 4-vinylpyridine gave atactic polymers.     

Field ionization mass spectrometry—IV. Isotopically labeled heptanals

The field ionization (FI) mass spectra of n-heptanal and a series of deuterium labeled analogs have been studied, with the objectives of initiating systematic investigations of reaction mechanisms of FI produced ions and to permit comprison with those found for other ionization processes. It is now recognized that FI ions have: (a) lower average internal energies and (b) shorter residence times than similar ions generated by electron-impact (EI), and the possibility exists of H/D-randomization occuring in ions formed by desorption from the emitter, by unimolecular decomposition close to the emitter and by either ‘fast’ or ‘slow’ metastable decompositions. In this study only the peak shifts of normal ions could be utilized; accurate mass measurements of all major ions revealed elemental compositions similar to EI. A site-specific McLafferty rearrangement gave the base peak at m/e 44 ([C₂H₄O]^+.), although the apparently complementary ion at m/e 70 ([C₅H₁₀]^+.) arose in a less specific process. Ions at m/e 43 ([C₃H₇]⁺) and 71 ([C₅H₁₁]⁺ 80%; [C₄H₇O]⁺ 20%) were apparantly generated without significant H/D-scrambling. Of special interest was the observation of the rearrangement ion at m/e 86 ([C₅H₁₀O]^+.) caused by loss of C-2 and C-3 as C₂H₄, as found for EI. It is concluded that at least in this system, decomposing molecular ions formed: (a) in the gas phase extremely close to the emitter and/or (b) on the emitter surface, have lifetimes sufficiently short to preclude complete H/D randomization. The results also provide evidence for common fragmentation mechanisms for heptanal molecular ions at both the low end and the high end of the energy distribution.     

Electron-impact studies—L: Skeletal-rearrangement fragments in the mass spectra of diphenylpyrazoles and -isoxazoles

The mass spectra of all diphenylpyrazoles and -isoxazoles contain rearrangement peaks at m/e 165 [C₁₃H₉]⁺. In addition, the spectra of 3,5-diphenylisoxazoles contain peaks at m/e 180 [C₁₃H₁₀N]⁺, which are produced by specific phenyl migrations. The mechanisms of both rearrangement processes have been studied by deuterium labelling.     

The structure of chlorinated poly(vinyl chloride). VI. Comparison of the chlorination of poly(vinyl chloride) and β,β-d2-poly(vinyl chloride) with 1H-NMR and 13C-NMR spectroscopy

Samples of chlorinated poly(vinyl chloride) (CPVC) and chlorinated β,β-dideuterated poly(vinyl chloride) (β,β-d₂-CPVC) were prepared under identical reaction conditions. The microstructure of CPVC and β,β-d₂-(CPVC) was characterized by a combination of ¹H-NMR, ¹³C-NMR spectroscopy, and analytically determined chlorine content. A difference was observed in the reaction rates of chlorination of PVC and β,β-d₂-PVC, and, in their thermal chlorination in solution, also in the structure of the chlorinated products. It was proved that in the chlorination of β,β-d₂-PVC a new chlorine atom can also enter the original? CHCl? group. The results are discussed from the standpoint of the chlorination mechanism.     

Electron impact ionization mass spectra of some substituted dipyrido[1,2-a:4,3-d]pyrimidinones

The electron impact ionization mass spectra of dipyrido [1,2-a:4,3-d]pyrimidinones are strongly influenced by the degree of aromaticity of the fused rings. The molecular ions of the compounds are fairly stable. The main routes of fragmentation involve formation of the [M – H]⁺ ion and loss of substituents, H₂CN˙, CO and alkyl radicals.     

Chemical ionization mass spectrum of peroxyacetylnitrate

The chemical ionization mass spectrum of peroxyacetylnitrate, a major component of photochemical smog highly toxic to man and plants, was obtained using both methane and isobutane as reagent gas. The spectrum contains a [M + H]⁺ ion at m/e 122, intense fragment ions at m/e 43 [CH,CO]⁺ and m/e 46 [NO₂]⁺, and less intense ions at m/e 61 [CH,ONO]⁺, m/e 77 [CH30NOz]⁺ and m/e 88 [⁺O?CCH₂ONO] formed by internal rearrangements. These results confirm the commonly accepted structure for peroxyacetylnitrate, CH₃(CO)OONO₂.