The mass spectra of trifluoroacetyl-2,5-diketopiperazines. II. cyclo-(-Val-Val/Leu/Ile), cyclo-(-Leu-Leu/Ile), and cyclo-(-Ile-Ile)

1979 ◽  
Vol 57 (15) ◽  
pp. 2052-2057 ◽  
Author(s):  
George P. Slater ◽  
Lawrence R. Hogge
Keyword(s):  
Mass Spectra ◽  
Molecular Ion ◽  
Alkyl Groups ◽  
Metastable Ions ◽  
Derivatives Of

The trifluoroacetyl derivatives of the 2,5-diketopiperazines cyclo-(-Val-Val/Leu/Ile), cyclo-(-Leu-Leu/Ile), and cyclo-(-Ile-Ile) were examined by GC–MS. The fragmentation of these compounds generally follows the same pathways as previously observed for the TFA-cyclo-(-Gly-X) series (X = Gly, Val, Leu, Ile). However, the spectra can be interpreted on the basis that the molecular ion fragments prior to, or after, one of the alkyl groups is eliminated as olefin. Some ion fragments indicate that both alkyl groups are eliminated but this does not appear to occur directly from the molecular ion. Support for fragmentation of the molecular ion by the suggested route is indicated by a number of isobaric ions although corresponding metastable ions were not observed.The spectra enable the compounds in the series TFA-cyclo-(-Val-X) (X = Val, Leu, Ile) to be readily identified but this is not the case for TFA-cyclo-(-Leu-Leu/Ile) and TFA-cyclo-(-Ile-Ile). However, all of these compounds can be distinguished from TFA-cyclo-(-Gly-X) and TFA-cyclo-(-Ala-X) (X = Gly, Val, Leu, Ile).

The mass spectra of trifluoroacetyl-2,5-diketopiperazines. I. cyclo-(-Gly-X), cyclo-(-Ala-X) (X = Gly, Val, Leu, Ile), and cyclo-(-Ala-Ala)

1979 ◽  
Vol 57 (15) ◽  
pp. 2037-2051 ◽  
Author(s):  
George P. Slater ◽  
Lawrence R. Hogge
Keyword(s):  
Mass Spectrum ◽  
Mass Spectra ◽  
High Resolution Data ◽  
Fragmentation Pathways ◽  
Molecular Ion ◽  
Metastable Ions ◽  
Fragmentation Patterns ◽  
The Individual ◽  
Derivatives Of ◽  
Resolution Data

The trifluoroacetyl derivatives of the 2,5-diketopiperazines cyclo-(-Gly-X), cyclo-(-Ala-X) (X = Gly, Val, Leu, Ile), and cyclo-(-Ala-Ala) were examined by GC–MS. The molecular ion was readily detectable only for TFA-cyclo-(-Gly-Gly) (m/e 306, 9%). For those compounds containing a valyl or leucyl/isoleucyl residue the ion of highest mass in the spectrum was formed by elimination of C3H6 or C4H8, respectively, from the molecular ion. In the TFA-cyclo-(-Gly-X) series this ion corresponded to the molecular ion of TFA-cyclo-(Gly-Gly) (m/e 306), and in the TFA-cyclo-(-Ala-X) series, to the molecular ion of TFA-cyclo-(-Ala-Gly) (m/e 320). The fragmentation patterns proposed for these compounds are based on the further degradation of these parent ions so that each compound within a series has a similar mass spectrum. However, sufficient differences were detectable in the various spectra to permit identification of the individual DKP's.Many of the fragmentation pathways devised to explain the mass spectra were supported by high resolution data and appropriate metastable ions.

Thio derivatives of β-Diketones and their metal chelates. XV. Mass spectra of cobalt(III) and rhodium(III) chelates of some fluorinated Monothio-β-diketones

1974 ◽  
Vol 27 (6) ◽  
pp. 1177 ◽  
Author(s):  
M Das ◽  
SE Livingstone
Keyword(s):  
Thermal Degradation ◽  
Mass Spectrometer ◽  
Mass Spectra ◽  
Cobalt Complexes ◽  
Metal Chelates ◽  
Complex Ions ◽  
Molecular Ion ◽  
Derivatives Of ◽  
Bivalent State ◽  
Cobalt Chelates

The mass spectra of the cobalt(111) and rhodium(111) chelates of the fluorinated monothio-β-diketones RC(SH)=CHCOCF3 (R = Ph, p-MeC6H4, p-BrC6H4, p-FC6H4, and 2-thienyl) and of the cobalt(111) chelate of CH3C(SH)=CHCOCF3 have been obtained. The cobalt chelates do not give a peak for the molecular ion because of thermal degradation to the cobalt(11) complex CO(RCS=CHCOCF3)2, which then undergoes reactions in the mass spectrometer. Fluorine migration occurs with cobalt but not with rhodium. The cobalt complexes give rise to more metal-containing fragments than their rhodium analogues. Mechanisms are proposed for the reactions involving the metal-containing fragments. Cobalt undergoes valency changes to give cobalt(11) and cobalt(1) complex ions, whereas rhodium undergoes a valency change to the bivalent state only.

Fragmentation and rearrangement processes in the mass spectra of perhalogenoaromatic compounds. Part X. Pentafluorophenyl dimethyl derivatives of group V

1976 ◽  
Vol 54 (9) ◽  
pp. 1478-1486 ◽  
Author(s):  
Timothy R. B. Jones ◽  
Jack M. Miller ◽  
J. Lowell Peterson ◽  
Devon W. Meek
Keyword(s):  
Mass Spectra ◽  
Energy Spectra ◽  
Group V ◽  
Fragmentation Pathways ◽  
Transfer Processes ◽  
Metastable Ions ◽  
Ion Kinetic Energy ◽  
Derivatives Of ◽  
Rearrangement Processes ◽  
Resolution Study

A comprehensive low-resolution study of the mass spectra of the compounds C6F5M(CH3)2, where M = N, P, As, is described, fragmentation pathways being assigned with the aid of normal metastable ions and mass analyzed ion kinetic energy spectra (mikes). A comparison of these spectra has re-affirmed the absence of halogen transfer processes for atoms such as N which are incapable of providing the necessary vacant orbitals apparently prerequisite in the mechanisms. The influence of increased coordination to phosphorus and effects on halogen transfer processes are discussed with respect to the mass spectra of the compounds C6F5PX(CH3)2, X = O, S, Se and the gold adducts C6F5P(CH3)2•AuX, X = Cl, Br, I.

Thio derivatives of β-Diketones and their metal chelates. XVII. Mass spectra of iron(III) and ruthenium(III) chelates of some fluorinated Monothio-β-diketones

1974 ◽  
Vol 27 (10) ◽  
pp. 2115 ◽  
Author(s):  
M Das ◽  
SE Livingstone
Keyword(s):  
Thermal Degradation ◽  
Mass Spectrometer ◽  
Mass Spectra ◽  
Metal Chelates ◽  
Iron Chelates ◽  
Molecular Ion ◽  
Derivatives Of

The mass spectra of the iron(111) and rhodium(111) chelates of the fluorinated monothio-β-diketones RC(SH)=CHCOCF3 (R = Ph,p-MeC6H4, 2-thienyl) have been obtained. Whereas the ruthenium(111) chelates give a peak for the molecular ion, the iron(111) chelates do not, due to thermal degradation to the iron(11) complex Fe(RCS=CHCOCF3)2 which then undergoes reactions in the mass spectrometer. Fluorine migration occurs with two of the iron chelates but not with the ruthenium chelates. Mechanisms are proposed for the reactions of the ruthenium chelates.

The mass spectra of Schiff bases. I. Simple fissions and rearrangements

1966 ◽  
Vol 19 (2) ◽  
pp. 251 ◽  
Author(s):  
DJ Elias ◽  
RG Gillis
Keyword(s):  
Double Bond ◽  
Electron Impact ◽  
Schiff Bases ◽  
Mass Spectra ◽  
Hydrogen Transfer ◽  
Molecular Ion ◽  
Ring Carbon ◽  
Carbon Bonds ◽  
Ring Nitrogen ◽  
Derivatives Of

Under electron impact, Schiff bases give a stable molecular ion which undergoes simple fission at the ring-nitrogen and ring-carbon bonds. Ortho substitution leads to ions derived from five-membered heterocycles. Derivatives of o-methoxy-benzaldehyde exhibit a two-hydrogen transfer with fission of the azomethine double bond to give the amine radical-ion.

Thio derivatives of b-diketones and their metal chelates. XIII. Mass spectra of zinc and nickel chelates of some fluorinated monothio-b-diketones

1974 ◽  
Vol 27 (1) ◽  
pp. 53 ◽  
Author(s):  
M Das ◽  
SE Livingstone
Keyword(s):  
Metal Ion ◽  
Mass Spectra ◽  
Metal Chelates ◽  
Cyclic Structure ◽  
Molecular Ion ◽  
Metal Free ◽  
Strong Peak ◽  
Nickel Chelates ◽  
Valence Change ◽  
Derivatives Of

The mass spectra of the zinc(11) and nickel(11) chelates of four fluorinated monothio-β-diketones, RC(SH)=CHCOCF3 (R = Ph, p-MeC6H4, 2-thienyl, Me), have been obtained. The mass spectra of the nickel chelates have considerably more peaks due to metal-containing species than the spectra of the zinc chelates, while the reverse is true for the metal-free fragments. All the zinc chelates give peaks for M (molecular ion), M ? CF3, M - L (LH = monothio-β-diketone), M - L ? CF2, LH, L, L - F, RCSCH and RCS. All the nickel chelates give peaks for M, M - F, M ? CF3, M - COCF3, M - L, M- 2L and L. In addition, some of the metal chelates give other peaks. Mechanisms are proposed for the reactions giving rise to some of these species. All the zinc and nickel chelates give a strong peak due to L+ arising from a valence change of the metal ion from the bivalent to the univalent state as follows: [Me11L2]+ → L+ + Me1L (Me = Zn, Ni). It is suggested that the ion L+ has a resonance-stabilized cyclic structure.

Electron-Impact Mass-Spectra of 3-Alkyl-2,1-benzisoxazoles

1991 ◽  
Vol 44 (6) ◽  
pp. 863 ◽  
Author(s):  
LK Dyall ◽  
JA Ferguson
Keyword(s):  
Electron Impact ◽  
Mass Spectra ◽  
Methyl Ethyl ◽  
Molecular Ion ◽  
Partial Decomposition ◽  
Methyl Cyanide ◽  
Alkyl Groups ◽  
Alkyl Cations ◽  
Electron Impact Mass ◽  
Impact Mass

3-Alkyl-2,1-benzisoxazoles underwent complex fragmentations under electron impact, and the balance between available pathways changed considerably across the range of alkyl groups (methyl, ethyl, isopropyl and t-butyl). The primary loss of CO is accounted for in terms of rearrangement of the initial molecular ion to an alkylimine ketene species. The 3-methyl compounds lost methyl as methyl cyanide, acylium cation or ketene, but the higher alkyl groups were chiefly lost as alkyl cations or by internal fragmentations in which some novel ortho-effects were noted. Most of these pathways were confirmed by B/E linked scans, and useful comparisons were made with the e.i . spectra of N- alkylanthranilic acids. All of these isoxazoles underwent partial decomposition on the heated probe.

Inductive effect in EI-mass spectra of some 5,6-dihalogenides and 5,6-halohydrins of 5α-cholestan-3β-ol and 3β-acetoxy-5α-cholestane

1982 ◽  
Vol 47 (11) ◽  
pp. 2946-2960 ◽  
Author(s):  
Antonín Trka ◽  
Alexander Kasal
Keyword(s):  
Mass Spectra ◽  
Inductive Effect ◽  
Molecular Ions ◽  
Hydroxyl Group ◽  
Halogen Atoms ◽  
Derivatives Of

Partial EI-mass spectra of 3β-hydroxy- and 3β-acetoxy-5α-cholestanes substituted in positions 5α-, 6β- or 5α,6β- with a hydroxyl group or halogen atoms (fluorine, chlorine, bromine) are presented. The molecular ions of 5α,6β-disubstituted derivatives of 3β-hydroxy-5α-cholestane (or of its 3-acetate) are considerably more stable than the corresponding monosubstituted derivatives if at least one of the pair of the vicinal substituents is chlorine or fluorine. This increase in stability, most striking in 5α- and 6β-fluoro compounds, is explained by the inductive effect.

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