Metastable Ion Peak (or Metastable Peak)

2016 ◽  
Keyword(s):  
Metastable Peak

The mass spectra of pyrimidines. II. 2(1H)-Pyrimidinethiones and some N(1)-substituted derivatives

1984 ◽  
Vol 62 (11) ◽  
pp. 2340-2343 ◽  
Author(s):  
Robin T. B. Rye ◽  
Oswald S. Tee ◽  
Eva M. Kazdan
Keyword(s):  
Kinetic Energy ◽  
Energy Release ◽  
Mass Spectra ◽  
Kinetic Energy Release ◽  
Exact Mass ◽  
Metastable Peak ◽  
Fragmentation Pathways

The EI induced fragmentation of 2(1H)-pyrimidinethione (1), some N(1)-substituted derivatives, and 2(1H)-pyrimidineselenone (4) have been studied. Principal fragmentation pathways have been identified using 2H-labelling, metastable defocussing, and exact mass measurements.The fragmentations of 1 and 4 generally parallel those reported for 2(1H)-pyrimidinone. In contrast to the oxo-compound, however, direct expulsion of the exocyclic hetero atom is significant in the fragmentation of 1, and dominates the spectrum of 4.Based on metastable peak abundances and kinetic energy release measurements, it is postulated that the [M – H]+ entity generated from N-ethyl-2-pyrimidinethione has a thiazolinium structure.

Isomeric cyclic [C6H10]+• ions. The energy barrier to ring opening

1979 ◽  
Vol 57 (3) ◽  
pp. 348-354 ◽  
Author(s):  
Peder Wolkoff ◽  
John L. Holmes
Keyword(s):  
Activation Energy ◽  
Kinetic Energy ◽  
Energy Barrier ◽  
Ring Opening ◽  
Reaction Pathway ◽  
Molecular Ions ◽  
Metastable Peak ◽  
Molecular Ion

Appearance energies and metastable peak shapes for methyl loss from the molecular ions of cyclohexene, methylcyclopentenes, methylenecyclopentane, bicyclo[3.1.0]hexane, and 2-methyl-1,4-pentadiene indicate that they have a common reaction pathway which produces [cyclopentenium]+ as the daughter ion at threshold.From measurements of appearance energies and from relative peak abundances and kinetic energy releases for the metastable losses of CH3• and labelled methyl from the deuterium labelled cyclic [C6H10]+• molecular ions it was concluded that: (a) H/D mixing in [cyclohexene]+• occurs in the intact ring prior to a concerted methyl extrusion; (b) [methylcyclopentenes]+• loses methyl without any H/D mixing at or near to threshold by a straight C—C cleavage, possibly via the 3-isomer. Methyl losses involving H/D mixing are preceded by ring opening which has an activation energy of ca. 1 eV. However, [cyclopentenium]+• is again the daughter ion; (c) methylenecyclopentane and bicyclo[3.1.0]hexane molecular ions isomerize to methylcyclopentenes prior to methyl loss.H/D mixing (prior to methyl loss) in the molecular ion 1,1-2H2-2-methyl-1,4-pentadiene takes place before cyclisation to methylcyclopentene.

Mass spectral studies of some desaurins and related 3,5-bismethylene-1,2,4-trithiolanes

1968 ◽  
Vol 46 (3) ◽  
pp. 365-375 ◽  
Author(s):  
Peter Yates ◽  
Thomas R. Lynch ◽  
L. S. Weiler
Keyword(s):  
Carbonyl Group ◽  
Mass Spectra ◽  
Molecular Ions ◽  
Spectral Studies ◽  
Mass Measurements ◽  
Metastable Peak ◽  
Fragmentation Pathways ◽  
Mass Spectral ◽  
Accurate Mass Measurements ◽  
Doubly Charged

The mass spectra of three desaurins and four related 3,5-bismethylene-1,2,4-trithiolanes have been interpreted with the aid of metastable peak assignments and accurate mass measurements. Strong molecular ion peaks are observed in the case of the aryl desaurins but not in that of their trithiolane counterparts. A variety of fragmentation pathways are postulated for the molecular ions, including cleavage on either side of a carbonyl group and elimination of a molecule of acylthioketene. In the case of the desaurins the latter process results in the formation of acylthioketene molecular ions, which could be distinguished from the doubly charged desaurin molecular ions. In the case of two of the trithiolanes, it is proposed that the ions resulting from loss of acylthioketene from the molecular ions undergo a novel type of McLafferty rearrangement and loss of carbon suboxysulfide to give aryl mercaptan molecular ions.

An anomalous “metastable peak” in the mass spectrum of methanol

1968 ◽  
Vol 0 (5) ◽  
pp. 265-266 ◽  
Author(s):  
J. H. Beynon ◽  
A. E. Fontaine ◽  
G. R. Lester
Keyword(s):  
Mass Spectrum ◽  
Metastable Peak
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