Mass spectral fragmentation ethers

The reaction products from 2,4-dichlorophenol were tetrachloro-phenoxyphenols and tetrachlorodihydroxybiphenyls (Figure 5), as determined from their mass spectra and those of their methyl ethers. 4,6-Dichloro-2-(2, 4 -dichlorophenoxy)phenol (V) was the major phenoxy-phenol the mass spectral fragmentation pattern of o-hydroxyphenol ethers is quite characteristic since a hydrogen transfer occurs during the fragmentation (Figure 6). A trace of a trichlorophenoxyphenol also was detected and was formed presumably by the unsensitized reductive loss of chlorine, discussed previously. 

Two new alkaloids, ALC-1 and ALC-2, were isolated from H. salicifolia by Dominquez et al. (20). Mass spectral fragmentation and properties of methyl ethers suggested that they were stereomers of lythrine. 

Fig 5. Mass spectral fragmentation of dihydrovindoline ether dimer (45) (52). 

The conversion of shionone into dihydrobaccharis oxide (80) has been reported.59 3/3,4/3-Epoxyshionane (81), on treatment with boron trifluoride etherate, afforded (80) and bacchar-12-en-3j8-ol (82). The high-resolution mass spectral fragmentation patterns of a number of shionane and friedelane derivatives have been examined.60... 

Djerassi7 has reported extensive studies on the mass spectral fragmentation of trimethylsilyl ethers. 

The localisation of hydroxy-groups from study of mass spectra of the derived ketones has been described. 5a- and 5 -3-oxo-steroids can generally be distinguished by their characteristic fragmentations. The same compounds can be converted into their enol trimethylsilyl ethers, having the olefinic bond respectively in the A - and A -positions. Each affords a distinctive mass spectral fragmentation pattern. ... 

The determination of the position of the double bond in linear alkenes by oxyselena-tion and GC-mass spectrometry was described by Francis and Tande [265]. Mixed ethers containing oxygen and selenium, formed by single-step conversion of alkenes, showed mass spectral fragmentation characteristics that depend on the original doublebond position. 

Kurokawa S, Elix JA, Watson PL, Sargent MV (1971) Parmelia notatay a new lichen species producing two new depsidones. J Jpn Bot 46 33-38 Kutney JP, Sanchez IH, Yee TH (1974) Mass spectral fragmentation studies in usnic acid and related compounds. Org Mass Spectrom 8 129-146 Laake Oy (1960) Institutional advertising of the La e Oy Pharmaceutical Manufacturers, Turku, Finland Lajide L (1984) Lichen depsides, depsidones and diphenyl ethers isolation, structure determination and synthesis. Thesis, Australian National Univ, Canberra Lam JKK, Sargent MV, Elix JA, Smith DO N (1972) Synthesis of valsarin and 5,7-dichloroemodin. J Chem Soc Perkin Trans 1 1466-1470... 

A decision in favour of the hydroxylation pattern shown in (140) came from n. m. r. spectroscopy of the dimethyl ether (144) (obtained from disidein by methanol-hydrochloric acid treatment), using a shift reagent [Eu(fod3 — d9)a], which induced about the same shift for the 17-methyl resonance and for the benzylic methylene. Evidence for the m 3-methoxy groups in (144) was obtained by DDQ oxidation, which gave a mixture of a methoxy-/ -quinone and a methoxy-o-quinone. Support for the proposed pentacyclic skeleton for the sesterterpene moiety of disidein was also obtained from mass spectral fragmentation studies. 

Osmiumfvi).—The i.r. spectrum of [OsOCl ] has been recorded in the gas and liquid phases, and in solution. While the exact geometry could not be deduced, evidence was obtained for facile co-ordination of acetone or ether to the species in inert solvents. A mass spectral study of this complex reveals a complex fragmentation pattern, including the previously unknown [OsOClj] species. ... 

In addition to the intact residues of 2,4,5-T excreted in the rat urine, mass spectral evidence was obtained for the presence of the metabolite TCP and a trichlorodihydroxybenzene isomer, which were observed as their mono- and diethyl ether derivatives, respectively. Thus, TCP ethyl ether displayed a molecular ion at m/e 224 and characteristic fragments at m/e 196 and m/e 160 owing to consecutive elimination of ethylene and HCl from the parent ion. The fragmentation pattern of 2,4,5-tri-chloropenol was observed to exhibit similar behavior below m/e 196. 

The mass spectral evidence for the trichlorodihydroxybenzene diethyl ether included a molecular ion of m/e 286 and significant fragment ions at m/e 240, m/e 212, and m/e 176 arising from the consecutive elimination of two molecules of ethylene and one molecule of HCl. 

Because the methoxymethylene group attached at C-4 normally is not involved in the fragmentation of these alkaloids, the mass spectra of various carbinolamine ethers were utilized to determine the nature of the C-4 substituents. From the published mass spectral data, no definite conclusion about the nature of C-4 groups can be predicted. 

The mass spectrum of the corresponding trimethyl-silyl ether derivative is shown in Figure lb, and an important advantage of this derivatization is immediately apparent in the prominent [M —CH3] ion at m/z 173. This ion allows the estimation of the molecular weight of the derivative in cases where a molecular ion is absent. In addition, because the fragmentation pattern is characteristic of the molecule, it may be used as a mass spectral fingerprint to confirm the identity of the GC peak, and libraries of reference spectra are readily available. Trimethylsilylation is one of the most common derivatizations in GC-MS. Further details and examples are given later in the section on silylation. 

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