The fragmentation of 2-aminooxazoles under electron impact

The 70 eV electron impact mass spectra of six 2-aminooxazoles are discussed in detail with the aid of exact mass measurements, metastable ion detection in the defocused mode and labelling experiments. The fragmentation is markedly influenced by strong electron donating substituents at the 2-position. Some 2-acetylamino and 2-diacetylamino derivatives have also been considered, which lose ketene from [M]⁺? giving the corresponding aminooxazole molecular ions. The mass spectral behaviour is peculiar and the most important differences between the fragmentation pathways of these compounds and those reported in the literature for oxazole (alkyl and aryl) derivatives are outlined. The mass spectrum of 4-methyl-5-phenylimidazol-2-one is compared with that of the isomeric 4-methyl-5-phenyl-2-aminooxazole.     

Ortho effect: The fragmentation of isopropyl 2-hydroxychlorocarbanilates

The mass spectra of isopropyl 2-hydroxychlorocarbanilate indicate a preferential ortho intramolecular rearrangement which yields a chloro 2-benzoxazolinone intermediate ion. A com-parison of the fragmentation of ortho, meta and para hydroxy analogs of isopropyl 3-chlorohydroxy-carbanilate indicates the existence of an ‘ortho effect’ during the fragmentation of isopropyl-chloro 2-hydroxycarbanilates.     

The fragmentation of isotetronic acids under electron impact

The mass spectral fragmentation of eleven α-hydroxybutenolide compounds (isotetronic acids) are reported. The main features are carboxyl and consecutive carbon monoxide expulsions. Masses were determined using high resolution techniques, metastable transitions were detected by defocusing experiments, and pathways were further documented by isotopic labelling experiments.     

The fragmentation of 1-phenyl-2-propen-1-ol under electron impact

The electron impact mass spectra of 1-phenyl-2-propen-1-ol and its specifically deuterated analogues have been investigated. Most of the decomposition pathways involve skeletal rearrangements or hydrogen atom transfers, such that a rearrangement of the excited molecular ions of 1-phenyl-2-propen-1-ol to molecular ions of cinnamic alcohol and/or cinnamaldehyde can be anticipated.     

The fragmentation behaviour of some spirobenzthiazoles under electron impact

The electron impact induced fragmentations of ten spiro-benzthiazoles have been studied. The principal decomposition reactions have been elucidated by metastable studies, exact mass measurements, and by deuterium exchange of the imino hydrogen. The primary fragmentation step is an α-cleavage reaction, which leads to ring opening of the ring fused to the benzthiazole moiety of the molecule. The subsequent decompositions resemble those of cyclohexylamines. They follow a general pattern, the details of which are discussed with respect to the nature and position of the heteroatom in the saturated ring.     

Ortho effect of the nitro group in the fragmentation of 1-phenyl-3-nitrophenyl-2-pyrazolines

Electron impact mass spectra and mass-analysed ion kinatic energy spectra of the title compounds are discussed. The characteristic fragment ions of the ortho isomer are shown by high resolution and kinetic energy release measurements to involve the transfer of hydrogen to the nitro group and oxygen from the nitro group to the pyrazoline carbon.     

The fragmentation of isotetronic acid O-methyl ethers under electron impact

The mass spectra of a series of methyl ethers of isotetronic acids have been examined and the modes of fragmentation rationalized on the basis of two general schemes.     

Main fragmentation routes of functionally substituted cyclopropenes under electron impact

The behaviour of substituted cyclopropenes under electron impact is to a large extent determined by the presence of the unsaturated three-membered ring which is capable of efficient delocalization of the positive charge. The loss of one of the substituents at the C(3) position of the small ring is characteristic for the fragmentation of cyclopropenes; the loss of the substituent which is less electron donating occurs preferentially. The presence of substituents with heteroatoms on the three-membered ring may lead to changes in the fragmentation scheme characteristic for the specific set of substituents.     

The fragmentation of 5- and 3-substituted thiophene-2-carboxamides under electron impact

The 70 eV electron impact mass spectra of twelve 5- and 3-substituted thiophene-2-carboxamides are discussed with the aid of exact mass measurements and labelling experiments. All mass spectra exhibit pronounced molecular ions. Some isomeric 5- and 3-substituted title compounds can be differentiated by mass spectrometry. The fragmentation is influenced by a strong ‘ortho-effect’ which activates the NH₃ elimination. In the other cases the most important fragmentation is NH₂˙ loss, followed by CO elimination.     

Mass spectrometry of macroheterocycles. 2. Characteristics of the fragmentation of azacrown ethers under electron impact

The fragmentation of aza-crown and diaza-crown ethers under electron impact was studied. It is shown that for the former the primary pathways of fragmentation of the molecular ions involve the intracyclic migration of a hydrogen atom and the elimination of C₂H₃O and CH₂OH particles. A characteristic feature of the diaza-crown ethers is the ejection of a divinylaminyl radical.For Communication 1 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 242–246, February, 1992.     

The electron impact induced fragmentation of 1,3-diphenyl-2-pyrazoline

The electron impact induced fragmentation of 1,3-diphenyl-2-pyrazoline was studied by nitrogen-15, carbon-13 and deuterium labelling, substitution in the para position of one of the phenyl rings by fluoro and methoxy groups, and ion kinetic energy spectroscopy, as well as accurate mass measurements. In the fragmentation pathway observed all the ions in the mass spectrum of 1,3-diphenyl-2-pyrazoline (except m/e 103) originate from the molecular ion, which in all compounds is the base peak. The formation of prominent fragment ions is discussed.     

Ortho effects in mass spectrometric fragmentation processes

The mass spectra of the phenylhydrazones and 2,4-dinitrophenylhydrazones of ortho substituted benzaldehydes and acetophenones (X = I, Br, Cl, OCH₃, OH) show characteristic [M ? X]⁺ ions which allow the ortho derivatives to be distinguished from their meta and para isomers.     

The effect of the strucutre of alkylferrocenes on their fragmentation types upon electron impact

The mass spectra of eight alkylferrocenes: 1,1′- ;dimethyl-, ethyl-, 1,1′-diethyl-, 1,1′-di-n-propyl-, 1,1′-diisopropyl-, 1,1′-di-n-butyl-, 1,1′-di-t-butylferrocene and tetra-t-butylferrocene, are reported in detail. General and specific fragmentations of these compounds are discussed.     

An unusual electron impact induced fragmentation of methylbenzofurazans

The electron impact mass spectra of 4-and 5-methylbenzofurazans exhibit an ion corresponding to the loss of CHO from the molecular ion. Loss of NO from the molecular ion is quite unimportant, in contrast to the behaviour of benzofurazan and some other substituted benzofurazans, in which loss of NO is the dominant process.     

Highly specific fragmentation processes of isomeric mixed esters of phenylsuccinic acid under electron impact

Isomeric mixed dialkyl phenylsuccinates, PhCH(COOR)CH₂COOR′, undergo a highly specific elimination of ROH under electron impact. A deuterium-labelling study showed that the hydrogen atom from the benzylic position 2 is abstracted in this process. These results suggest the occurrence of a ‘hidden’ hydrogen migration of the benzylic hydrogen atom to the carbonylic oxygen of the remote ester group, followed by the elimination of ROH from the adjacent ester group with the involvement of that hydrogen. Alkoxyl group migrations resulting in the formation of [PhCH?OR]⁺ and [PhCH?OR′]⁺ ions are less specific, although the migration of the remote R′O˙ is significantly preferred in all the pairs of isomers examined. Mechanisms are suggested for the formation of the two ions.