Mass spectrometric studies—II: Mass spectrometric studies of maleimides and benzaldazine adducts. Identification of solid mixtues

It has been found by mass spectrometric studies that the so-called ‘1:1-adduct’ formed by N-( nbutyl)maleimide and benzaldazine, is in fact a solid mixture of one part bis-imide L and one part benzaldazine. Bis-imide L is one of the three stereoisomeric products obtained by the addition of two mole of N-( n-butyl)malemide and one mole of benzaldazine. The three stereoisomeric bis-imides gave identical mass spectra. Mass spectra of bis-imide M and bis-imide M- d2 are discussed, and confirm the proposed structures of perhydroprazolo-pyrazole derivatives for these 1:2-adducts.     

Mass spectrometric studies of peptides—VI:. Applications of metastable ion and collisional activation spectra

An unambiguous differentiation between leucine and isoleucine residues in peptides is possible with unimolecular metastable ion (MI) and collisional activation (CA) spectra. The immonium ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm [Y}\!\mathop {\rm N}\limits^{\rm + } {\rm H = CHC}_{\rm 4} {\rm H}_{\rm 9} {\rm ]} $\end{document}, which is present in the normal mass spectra of all leucine or isoleucine containing peptides, yields MI spectra with which this differentiation can be made with high sensitivity. The MI and CA spectra of other peptide fragments are also applicable in particular cases. MI and CA spectra can also be used to obtain information on the amino acide sequences of individual ions. In general more extensive sequece information is available from CA than from MI spectra. This information appears to be particularly promising for the sequencing of oligopeptide mixtures or of ions produced by field or chemical ionization.     

Mass spectrometric studies of diterpenes: VIII—Epimers

Diterpene epimers differing with respect to orientation of a secondary hydroxyl group, ring fusion or configuration at an asymmetric centre carrying carbon–carbon linked substituents were studied, and certain stereostructural-spectral correlations were achieved for the first two groups. Each of the compounds examined was subjected to multiple scanning at both high and low electron voltage to allow computer assisted statistical calculation and comparison of intensity intervals at a predetermined confidence level for total ion currents and selected peaks.     

Mass spectrometric characterization of telechelic prepolymers and addition polymers of DGEBA–aliphatic amines

Plasma desorption (PD) mass spectra of high molecular weight addition polymers of 2.2-bis-[4-(2.3-epoxypropoxy)phenyl]propane (DGEBA) and benzylamine show protonated molecular ions of the intact polymers and oligomer molecules. In the spectrum of a DGEBA/N,N′-dibenzyl-5-oxanonanediamine-1.9 addition polymer only fragments of the oligomers and a cyclic oligomer are observed. In both polymer spectra there is no indication for side reactions during the addition polymerization such as ether formation. Fast-atom bombardment (FAB) spectra of telechelic prepolymers having amino end groups show the regular oligomers with increasing degree of polymerization and the expected fragmentation products. Only prepolymers with epoxide end groups contain the regular prepolymers as well as side reaction products which are formed by reactions of the telechelics and DGEBA or by reaction of themselves. © 1996 John Wiley & Sons, Inc.     

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

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.     

Heterocyclic studies—XXVIII Mass spectra of some 5-trifluoromethylpyrimido-(5,4-e)as-triazines

Fragmentation of 7-substituted 5-trifluoromethylpyrimido(5,4-e)as-triazines is dominated by consecutive losses of N₂ and HCN from the triazine ring. Deuterium labelling, accurate mass measurements and spectral changes with substitution patterns confirm the fragmentation pathways. Comparison of the spectra with those of corresponding pteridines indicates that the 1,2,4-triazine ring fragments much more readily than the pyrazine ring.     

Heterocyclic studies—XXIX: Mass spectra of some 1,2-dihydro-5-trifluoromethyl-pyrimido(5,4-E)AS-triazines

Mass spectra of five 7-substituted-1,2-dihydro-5-trifluoromethylpyrimido(5,4-e)as-triazine derivatives are recorded. Fragmentation pathways, elucidation of which was assisted by deuterium labelling and accurate mass measurements, are compared with those of corresponding heteroaromatic compounds. Loss of HF initiated the major breakdown pathways, unless a large 7-substituent was present, which then fragmented preferentially.     

Mass spectrometry of natural products: VIII—Mass spectrometric studies of ring a saturated gibberellins

The fragmentation behaviour of gibberellin A₁ methyl ester and gibberellin C methyl ester has been studied by means of positive and negative ion mass spectrometry, high resolution techniques and metastable ion transitions. The results obtained allow a mass spectrometric distinction to be made between both structural types.     

Mass spectrometric studies of cycloalkane-α-glycols

The mass spectral fragmentations of stereoisomeric cyclohexane-1,2-diols, p-menthane-2,3-diols, 1-hydroxycarvomenthols and 4-hydroxymenthols are discussed.     

Mass spectrometric investigation of carbohydrates

Conclusions The pathways of the fragmentation of completely methylated- methyl-L-arabopyranoside were studied in detail. The data obtained will serve as a basis for establishing the structure of the partially methylated pentopyranosides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 277–283, February, 1967.The authors would like to express their deep gratitude to R. A. Khmel'nitskii and A. A. Polyakova for kindly permitting the use of a mass spectrometer, equipped with a multiloop oscillograph.     

Mass spectrometric study of organocyclosiloxanes

Organocyclosiloxanes of various chemical structures were studied by mass spectrometry using different ionization methods. The electron ionization mass spectra contain no peaks of molecular ions, and the main fragment ions are formed due to complicated rearrangements in a molecular ion, which provides no comprehensive view about the molecular structure. The desorption spectra exhibit peaks of quasimolecular and fragment ions, which characterize both molecular weights and chemical structures of the compounds under study. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1746–1749, September, 2007.     

Mass spectrometric studies on gibberellins

Based on the element maps of twenty-two gibberellin methyl esters fragmentations are discussed, which are characteristic of the common structural features as well as structural modification in gibberellin homologues.     

Mass spectrometric investigation of carbohydrates

Conclusions The pathways of fragmentation of 2,3,4-tri-O-methyl--methyl-D-fucoside were studied. The data obtained serve as the basis for establishing the structure of partially methylated 6-deoxyhexoses.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 543–548, March, 1967.     

Mass spectrometric investigation of benzyliderieaniline

The mass spectral fragmentation of benzylideneaniline has been studied by deuterium labelling. Under electron impact, molecular ions undergo simple fission at the phenyl–N, phenyl–C and C?N bonds, hydrogen migration reactions, and skeletal rearrangement fragmentations. Except in the skeletal rearrangement reactions, hydrogen scrambling does not feature in benzylideneaniline upon electron impact.     

Conformational studies—I Conformational transmission

A semi-qualitative approach to the interpretation of the factors effecting conformational transmission is described.