Mass spectral breakdown

The mass spectral breakdown patterns for the two bridged compounds were very similar, with the exception that the peaks were one mass unit higher in the case of the oxygen-bridged material. Both compounds produced strong molecular ions at 533 (I) and... 

The pentanuclear carbido species Ms(CO)lsC (M = Fe, Ru, Os) have been prepared. The iron compound has been known for some considerable time (209), but the ruthenium and osmium complexes were prepared recently by pyrolysis reactions (210). The ruthenium adduct was only isolated in low yield (—1%), while the osmium complex was obtained in higher yield (—40%). The infrared spectrum and mass spectral breakdown pattern indicate a common structure to these compounds. The molecular structure of the iron complex is shown in Fig. 46. 

However, mass-spectral breakdown patterns of PI1OCH2CH2F suggest that a cyclic fluoronium ion can be observed as an ion-neutral complex in the gas phase [76], whilst calculations indicate that the fluoronium ion is more stable than the isomeric CH2CH2F ion [54]. Participation by fluorine remote from the reaction centre has been postulated to account for the product obtained from the reaction between 5-fluoro-l-pentyne and trifluoroacetic acid [46] (Figure 4.29). 

Part B This is structurally related to the co-occurring Callichilia monomer beninine (259) whose principal modes of mass spectral breakdown are shown these are characteristic of alkaloids of the aspidospermine type. ... 

Confirmation of this structure and, in particular, that the lactam carbonyl group is located at C-10, was obtained by chromic oxidation of pleiocarpine to CLXIII, a reaction which occurs in two steps, the first being the production of the five-membered pleiocarpine-10-lactam (cf. Volume VIII, pp. 439 and 361-363). The mass spectral breakdown of 10,11-dioxopleiocarpine (CLXIII) is unusual and the structures a and b may be proposed for its dominant peaks at m/e 310 and 240, respectively 31). 

The mass spectral breakdown of spirobenzylisoquinolines is appreciably affected by the position of the alkoxy substituents in ring D. ° If one or two ketonic functions are present in ring C, decarbonylation readily occurs. ... 

Mass spectral fragmentation patterns of alkyl and phenyl hydantoins have been investigated by means of labeling techniques (28—30), and similar studies have also been carried out for thiohydantoins (31,32). In all cases, breakdown of the hydantoin ring occurs by a-ftssion at C-4 with concomitant loss of carbon monoxide and an isocyanate molecule. In the case of aryl derivatives, the ease of formation of Ar—NCO is related to the electronic properties of the aryl ring substituents (33). Mass spectrometry has been used for identification of the phenylthiohydantoin derivatives formed from amino acids during peptide sequence determination by the Edman method (34). 

A comparative analysis of the El breakdown of arylsulfonyl-1//-azepines and IV-carboxymethyl-azepines carried out by Kulkami et al. <88OMS(23)240> indicates the primary breakdown is one of, respectively, N—S and N—C cleavage. In the latter case there is little indication of a competitive hydrogen capture by the azepine ring, a process preferred in the fragmentation of the isomeric aniline derivatives, nor could a correlation between mass spectral behavior and thermal and photochemical reactions be established. 

Breakdown graphs can be used to compare the energetic demands of those different fragmentation pathways, hi addition, breakdown graphs help to correlate ion internal energy distributions derived from other methods such as photoelectron spectroscopy [107] with mass spectral data. 

For either analytical approach, identification of the diagnostic cure system breakdown species is by reference to mass spectral libraries such as those produced by the National Institute of Standards and Technology (USA) (NIST), the Royal Society of Chemistry, Wiley/NBS (a. 12) and the US Environmental Protection Agency (EPA)/National Institute of Health (NIH). The mass spectra of the majority of species of interest are in these libraries and so, providing the knowledge to reconstmct cure systems is available, successful attempts can be made. 

Spectral data readily demonstrated the presence of indole, methyl /8-alkoxyacrylate, and hexoside functions. Ions in the mass spectrum of the acetate at m/e 183,182,169, and 168 (rather than the more common series m/e 184, 183, 170, and 169) indicated a tetrahydro-/3-carboline with a substituent a to N-4 however, the most distinctive feature was the ready loss of CO and C02 from the molecular ion which was attributed to the breakdown of a lactone. Accordingly, treatment with sodium methoxide opened the lactone ring, and reactylation gave a methyl ester pentaacetate... 

Spectral methods based on UV-visible spectrophotometry, laser-induced breakdown spectroscopy (LIBS), infrared (IR), Raman, nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS), thermoanalytical and chromatographic methods, especially liquid chromatography (LC) or gas chromatography (GC) combined with pyrolysis are most common. 

---