Fragmentation, organic mass spectrometry

Burgers PC, Holmes JL, Mommers AA, Szulejko JE and Terlouw JK (1984) Collisionally induced dissociative ionization of the neutral products from unimolecular ion fragmentations. Organic Mass Spectrometry 19 442-447. 

The electron ionization (El) source, formerly called electron impact, was devised by Dempster and improved by Bleakney [1] and Nier [2], It is widely used in organic mass spectrometry. This ionization technique works well for many gas-phase molecules but induces extensive fragmentation so that the molecular ions are not always observed. 

Another interesting rearrangement observed in the spectra of the Ar4Sn species occurs in the case of Ar = o-Tol for which a prominent peak corresponding to the ArSnCrHs ion has been identified. This fragment ion is not apparent in the spectra of the m- or p-tolyl system. This position effect has been claimed to be a typical example of the ortho effect that is commonly encountered in organic mass spectrometry . 

A wide variety of ionization techniques is available for organic mass spectrometry [1-2]. Analyte-ionization techniques can be classified as hard or soft , depending on the extent of fragmentation occttrring during the ionization... 

Inman, R. C., and M. P. Serve. 1982. The fragmentation behavior of the endo-and exo-octahydro-4,7-methano-lH-indene systems. Organic Mass Spectrometry 17 220. 

Figure 2 Electron impact fragmentation pathways of ephedrine-related compounds. (Reproduced with permission from Gadzala DE, Liu RH, Legendre MG, and Ku WW (1988) Mass spectra of derivatized ephedrine and norephedrine. Organic Mass Spectrometry 23,...

Mass Spectrometry. Green has given an exhaustive review of the consequences of molecular stereochemistry on organic mass spectrometry. In this, the stereoisomeric dependence of the electron-impact-induced rearrangements of alcohols and carbonyl compounds, the apparent electrocyclic fragmentations, and bond cleavage reactions are all covered in detail. 

The formation of fragments is one of the most u.seful characteristics of organic mass spectrometry. This becomes particularly apparent when no fragments are available, as with soft-ionization techniques, which produce almost exclusively molecular ions with negligible fragmentation. With electron impact, still the most important ionization technique, the majority of molecules form a large number of fragments. 

Figure 2.156 A typical line spectrum in organic mass spectrometry with a molecular ion, fragment ions and the loss of neutral particles (acetylsalicylic acid, CgHg04, M 180).

Scheme 1 Comparative fragmentation pathways of the Al(lll) and Fe(lll) acetylacetonates. Reproduced with permission of John Wiley Sons Limited from Lacey MJ and Shannon JS (1972) Valence-change in the mass spectra of metal complexes. Organic Mass Spectrometry 931-937.

Figure 3 El and CeFe+ charge exchange (CE) mass spectra of c/ s- and frans-4-methylcyclchexanol. Harrison AG and Lin MS, (1984) Stereochemical applications of mass spectrometry. 3. Energy dependence cf the fragmentation of stereoisomeric methyl cyclohexanols. Organic Mass Spectrometry 67-71. Copyright John Wiley Sons Limited. Reproduced with permission.

Bjorkhem, I., Gustafsson, J-A., and Sjovall, J. (1972) A novel fragmentation of trimethylsilyl ethers of 3P-hydroxy-5 -steroids. Organic Mass Spectrometry, 7,277-281. 

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