Mass spectrometry, fragmentation pathways

Mass spectral fragmentation pathways for some benzoxathiepins 9 and benzoxathiepinones 10 have been deduced <1999JCM584>. Mass spectrometry allows the distinction between the linear and angular benzofurazans (and furoxans) of the type 11 and 12 <1999JMP1137>. 

J.C. Oxley, J.L. Smith, J. Zhang, C Bedford, A Comparison of the Thermal Decomposition of Nitramines and Difluoroamines J. Phys. Chem. A., 105 (2001) 579-590. J. Zhang, J. Oxley, J. Smith, C. Bedford, R. Chapman Mass Spectral Fragmentation Pathways in Cyclic Difluoroamino and Nitro Compounds J. Mass Spectrometry, 35 (2000), 841-852. 

Mass Spectrometry The molecular ion peak is usually quite small m the mass spec trum of an alcohol A peak corresponding to loss of water is often evident Alcohols also fragment readily by a pathway m which the molecular ion loses an alkyl group from the... 

Mass Spectrometry Aldehydes and ketones typically give a prominent molecular ion peak m their mass spectra Aldehydes also exhibit an M— 1 peak A major fragmentation pathway for both aldehydes and ketones leads to formation of acyl cations (acylium ions) by cleavage of an alkyl group from the carbonyl The most intense peak m the mass spectrum of diethyl ketone for example is m z 57 corresponding to loss of ethyl radi cal from the molecular ion... 

Electron impact mass spectrometry has been employed to study the fragmentation patterns of isoxazolylmethyl- and bis(isoxazolylmethyl)-isoxazoles and the results are in agreement with proposed pathways (79AC(R)8l). Electron impact studies of nitrostyryl isoxazole (6) show fragmentation in a variety of ways. The standard loss of NO2 from the molecular ion... 

Diphenylthiirene 1-oxide and several thiirene 1,1-dioxides show very weak molecular ions by electron impact mass spectrometry, but the molecular ions are much more abundant in chemical ionization mass spectrometry (75JHC21). The major fragmentation pathway is loss of sulfur monoxide or sulfur dioxide to give the alkynic ion. High resolution mass measurements identified minor fragment ions from 2,3-diphenylthiirene 1-oxide at mje 105 and 121 as PhCO" and PhCS, which are probably derived via rearrangement of the thiirene sulfoxide to monothiobenzil (Scheme 2). 

Escherichia coli Adenine and adenosine are inhibitory74 and the synthesis of thiamine can be derepressed by culture in their presence.13,75 adth- Mutants are known.76 [l4C]Formate incorporates at C-2 of pyramine without dilution of molar activity. Glycine labeled with stable isotopes was fed to E. coli and the pyramine was analyzed by mass spectrometry. The two carbon atoms of glycine separated during the biosynthesis. The carboxyl was found12 at C-4, and the C-N fragment was the precursor of C-6-N-1. In conclusion, it is beyond doubt that pyramine synthesis follows the AIR pathway in E. coli. 

Figure 5.47 Fragmentations pathways for (a) non-demethylated, and (b) demethylated metabolites of Bosentan. Reprinted by permission of Elsevier Science from Exact mass measurement of product ions for the structural elucidation of drug metabolites with a tandem quadrupole orthogonal-acceleration time-of-flight mass spectrometer , by Hopf-gartner, G., Chernushevich, I. V., Covey, T., Plomley, J. B. and Bonner, R., Journal of the American Society for Mass Spectrometry, Vol. 10, pp. 1305-1314, Copyright 1999 by the American Society for Mass Spectrometry.

Figure 5.63 Proposed fragmentation pathway of the molecular ion from 8-hydroxy-2 -deoxyguanosine generated by negative ionization. Reprinted by permission of Elsevier Science from Comparison of negative- and positive-ion electrospray tandem mass spectrometry for the liquid chromatography-tandem mass spectrometry analysis of oxidized deoxynucleosides , by Hua, Y., Wainhaus, S. B., Yang, Y., Shen, L., Xiong, Y., Xu, X., Zhang, F., Bolton, J. L. and van Breemen, R. B., Journal of the American Society for Mass Spectrometry, Vol. 12, pp. 80-87, Copyright 2000 by the American Society for Mass Spectrometry.

Silane and hydrogen show relaxation patterns with the same characteristic time t, however, inverse signs. The fragmentation of silane induced by collisions with electrons, yields molecular hydrogen in an order of magnitude faster than the time resolution of the mass spectrometry setup, i. e. faster than 1 ms. Two possible pathways of silane fragmentation can be regarded ... 

Two-dimensional (2D) NMR is irrefutably the cornerstone of modem structure elucidation methods.1 Despite the inherently low sensitivity of NMR compared to other forms of analytical spectroscopy such as mass spectrometry and vibrational spectroscopy, NMR methods provide the means of establishing atom-to-atom connectivities that cannot be established by other methods. Supplemented by accurate mass measurements and fragmentation pathway information, NMR data can facilitate the elucidation of most small molecule structures. 

Fragmentation of amino acid-derived spirophosphorane 128 has been analyzed using field desorption (FD), El, and Cl mass spectrometry <1997RCM1825, 1997CCL629>. In spiro-crypta cyclophosphazene derivatives 129, the major decomposition pathway involved the initial cleavage of a P-Cl bond rather than cleavage of an exocyclic P-N bond as is normally seen for cyclophosphazenes <2004JST139>. 

Mass spectrometry has generally been employed in this series of compounds mainly for routine structure determination. The fragmentation pathways of some derivatives of 43 have been studied using accurate mass and metastable-transition measurements <1997JHC435>. 

There are still rather few fundamental studies of the mass spectrometry of organotin compounds, but the fragmentation pathways of organotin compounds have been further elucidated by means of tandem mass spectrometry.51,52... 

The mass spectrometer can be regarded as a kind of chemistry laboratory, especially designed to study ions in the gas phase. [1,2] In addition to the task it is usually employed for - creation of mass spectra for a generally analytical purpose - it allows for the examination of fragmentation pathways of selected ions, for the study of ion-neutral reactions and more. Understanding these fundamentals is prerequisite for the proper application of mass spectrometry with all technical facets available, and for the successful interpretation of mass spectra because Analytical chemistry is the application of physical chemistry to the real world. [3]... 

Note Although the discussion of common fragmentation pathways of organic ions is embedded here in the context of EI mass spectrometry, their occurrence is not restricted to this technique. The reactions of isolated gaseous ions do not directly depend on the ionization method, but are almost exclusively governed by intrinsic properties of the respective ion and by its internal energy (Chap. 2). 

Mass spectrometry is suitable for the identification of pyrrolo-benzodiaze-pines and the differentiation of their isomers (1996M1653). A structural distinction can be made easily from their mass spectra or the metastable mass-analyzed ion kinetic energy (MIKE) spectra, produced by their molecular or most intense fragment ions. Established fragmentation pathways have been supported by MNDO and AMI semiempiiical calculations. 

In an early study using electron impact (ei) mass spectrometry it was found that 2,3-diphenyldihydrodiazepine bases gave intense molecular ions and that the major breakdown pathway involves loss of the N(D—C(2) fragment (65CB3479). 

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