Non-rigid molecules. Part 4.—Hydrogen atom scrambling in the mass spectra of hydrocarbons

1980 ◽  
Vol 76 (0) ◽  
pp. 88-95 ◽  
Author(s):  
John Dalton ◽  
Lionel R. Milgrom
Keyword(s):  
Hydrogen Atom ◽  
Mass Spectra

Mass spectrometric studies. X. Phenacylpyridinium enol-betaines

1972 ◽  
Vol 25 (2) ◽  
pp. 345 ◽  
Author(s):  
IC Calder ◽  
QN Porter ◽  
CM Richards
Keyword(s):  
Hydrogen Atom ◽  
Mass Spectra ◽  
Parent Compound ◽  
Molecular Ions ◽  
Mass Spectrometric ◽  
Deuterium Labelling ◽  
E 92

Phenylpyridinium enol-betaines have mass spectra containing abundant molecular ions which decompose by loss of a hydrogen atom to give intense M- 1 species. Both ions eliminate CO and CHO units, and the courses of the various decompositions have been established by making use of deuterium labelling. The ion at m/e 92 in the spectrum of the parent compound is best described by an azatropylium structure.

The Fragmentation Mechanism of Cyclobutanol

1973 ◽  
Vol 51 (14) ◽  
pp. 2342-2346 ◽  
Author(s):  
John L. Holmes ◽  
Robin T. B. Rye
Keyword(s):  
Hydrogen Atom ◽  
Mass Spectra ◽  
Fragmentation Mechanism ◽  
Hydrogen Atoms ◽  
Specific Mechanism ◽  
Molecular Ion ◽  
Random Manner ◽  
Hydroxyl Hydrogen

The mass spectra of cyclobutanol and three 2H labelled analogs have been studied. The losses of C2H4 and C2H5• from the molecular ion involve specific fragmentations. Only CH3• loss from the α-cleaved molecular ion2 clearly involves hydrogen atom scrambling; this fragmentation also proceeds by a specific mechanism involving C-2 and hydroxyl hydrogen atoms. Loss of water from the molecular ion involves all the hydrogen atoms but in a complex, non-random manner.

scholarly journals Structure and thermal interconversion of cyclobilirubin IX α

1984 ◽  
Vol 218 (3) ◽  
pp. 667-676 ◽  
Author(s):  
S Onishi ◽  
I Miura ◽  
K Isobe ◽  
S Itoh ◽  
T Ogino ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Mass Spectra ◽  
Chemical Structure ◽  
Lactone Ring ◽  
Final Conclusion ◽  
Quaternary Carbon Atom ◽  
Methyl Group ◽  
Bilirubin Metabolism ◽  
To Come ◽  
Vinyl Group

One of the two main photoproducts in bilirubin metabolism during phototherapy in neonatal hyperbilirubinaemia is (EZ)-cyclobilirubin. However, it has not yet been possible to come to a final conclusion as to its chemical structure, despite the fact that much effort has been expended on the problem. The present paper demonstrates that (EZ)-cyclobilirubin is formed by the intramolecular cyclization of the C-3-vinyl group with the position at C-7 rather than at C-6, without delta-lactone-ring formation. The evidence comes from 13C-n.m.r. spectra, which indicate that an oxygen-bound quaternary carbon atom is not present, and from 1H-n.m.r. spectra, which indicate that the orientation of the methyl group at C-2 is equatorial; these findings are supported by mass spectra. The existence of both an epimeric relationship at C-7 between (EE)- and (EZ)-cyclobilirubins A and B and of steric isomers of the hydrogen atom and methyl group at C-2 is supported by the fact that the methyl-group protons at C-2 and C-7 are observed as a paired signal in 1H-n.m.r. spectra, and that new signals at C-7, C-2 and C-3 beta appear in 13C-n.m.r. spectra, that mass spectra of (EZ)-cyclobilirubins A and B are extremely similar and that, furthermore, thermal interconversion between (EE)- and (EZ)-cyclobilirubins A and B is observed.

scholarly journals The mass spectra of pyrimidines: 2(1H)-pyrimidinone and some N(1)-substituted derivatives

1982 ◽  
Vol 60 (14) ◽  
pp. 1800-1805 ◽  
Author(s):  
Eva M. Kazdan ◽  
Robin T. B. Rye ◽  
Oswald S. Tee
Keyword(s):  
Hydrogen Atom ◽  
Mass Spectra ◽  
Exact Mass ◽  
Fragmentation Pathways ◽  
Alternative Structures

The EI induced fragmentation of 2-pyrimidinone (1) and several N(1)-substituted derivatives has been studied. Principal fragmentation pathways have been identified using 2H labelling, metastable defocussing, and exact mass measurements.The fragmentation of 1 parallels that of cytosine. The hydrogen atom at C(4), and not the tautomeric hydrogen, is involved in the formation of the prominent [M – H]+ peak in the spectrum of 1; subsequent fragmentations of the [M – H]+ moiety contribute significantly to the spectrum.Side chain eliminations predominate in the mass spectra of the N(1)-substituted derivatives, but peaks characteristic of the pyrimidinone nucleus are observable in every case. Alternative structures for the [M – H]+ entity formed by H• loss from the substituent are proposed for the N-phenyl and N-benzyl compounds.

The Mass Spectra of Phenyl Methyl Ethers

1963 ◽  
Vol 16 (2) ◽  
pp. 219 ◽  
Author(s):  
CS Barnes ◽  
JL Occolowitz
Keyword(s):  
Hydrogen Atom ◽  
Electron Impact ◽  
Methyl Ether ◽  
Mass Spectra ◽  
Methyl Radical ◽  
Formaldehyde Molecule ◽  
Ether Oxygen

Fragmentation of a phenyl methyl ether under electron impact normally occurs by fission of either C-O bond to give ions due to loss from the parent of a methyl radical or, with rearrangement of one hydrogen, a formaldehyde molecule. In the latter case a hydrogen atom may be subsequently lost if a stable tropylium ion may thereby result. If there are present ortho- or para-substituents which are capable of forming a quinonoid structure involving the ether oxygen after removal of a methyl radical, then loss of formaldehyde does not occur.

THE MASS SPECTRA OF THREE DEUTERATED BUTANOLS

1958 ◽  
Vol 36 (6) ◽  
pp. 990-998 ◽  
Author(s):  
W. H. McFadden ◽  
M. Lounsbury ◽  
A. L. Wahrhaftig
Keyword(s):  
Hydrogen Atom ◽  
Mass Spectra ◽  
Excess Energy ◽  
Strong Tendency ◽  
Hydroxyl Group ◽  
Charge Localization

The mass spectra of 1,1-dideutero-l-butanol, 1,1,1,3,3-pentadeutero-2-butanol, and 1,1,1,2,3,3-hexadeutero-2-butanol have been obtained using 70-volt ionizing electrons. Comparison of the cracking patterns of the deuterated butanols with those of the undeuterated compounds confirms certain known features of the mass spectra of alcohols and reveals further information regarding the formation of several rearrangement ions. The strong tendency for alcohols to break at bonds beta to the hydroxyl group has been attributed to charge localization on the oxygen and this feature is used to explain the formation of many of the rearrangement ions. It is postulated that a hydrogen atom may be transferred to the electron-deficient oxygen and that the resulting structure distributes its excess energy and charge to give the activated complexes leading to the observed ions.

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