Dimethylated, mass spectral fragmentation

Example The oxidative addition of dimethyl disulfide (DMDS) transforms the double bond to its 1,2-bis-thiomethyl derivative (a). Induced by charge localization at either sulfur atom, the molecular ions of DMDS adducts are prone to a-cleavage at the former double bond position (b). This gives rise to sulfonium ions that are readily identified from the mass spectrum (Chap. 6.2.5). The method can be extended to dienes, trienes, and alkynes. [70,71] (For the mass spectral fragmentation of thioethers cf. Chap. 6.12.4). 

Mass spectral fragmentation pattern of dimethyl-nitramine, CH3N(N02)CH3, mw 90 Instrument, CEC 21-104 Ionization Voltage 70 eV... 

In the studies of the reactions of l-hydroxy-2-propanone and l-hydroxy-2-butanone and ammonium sulfide, despite four possible intermediates were predicted, only two intermediate compounds were tentatively identified by GC/MS in our study. The mass spectral data of these compounds showed very distinctive base peak p attem (Table I). These results agreed with results from previous study of five different 2-alkyl-2,4,5-trimethyl-2,5-dihydrooxazolines (7) which showed same mass spectral fragmentation pattern (m/z = 112) of same types of intermediate con5>ounds. Further study of GC/MS-CI results suggested their molecular weights and as the results, they were tentatively identified as 2-(1 -hydroxymethyl)-2,4-dimethyl-3-oxazoline, 2-( 1 -hydroxymethyl)-2,4-... 

The mass spectral fragmentation pattern of l,10-diethylbenzo[c]cinnoline (20), (Scheme 2) has been used in an explanation for the dilference in flash vacuum pyrolysis of this compound, which gives a complex mixture containing phenanthrene, and its dimethyl analogue which gives 1,8-dimethylbiphenylene as a major product. The base peak of (20) is that due to phenanthrene, mjz 178 <88JOC4333>. 

A comparison of the mass spectral fragmentation patterns of the dimethyl ester of caperatic acid (41) and the corresponding di(trideutero-methyl) ester located the position of the ester function in this molecule and established the structure as methyl 3,4-dicarboxy-3-hydroxyoctadecanoate (41) (25). In a corroborative chemical degradation (41) was oxidized by treatment with sodium bismuthate, whereupon methyl 3-oxo-octadecano-ate (42), the decarboxylation product of the initially formed P-keto-carboxylic acid, was detected (25). 

The solid compound has been characterized by elemental analysis, infrared and NMR ( H and spectroscopy, and X-ray diffraction. The analytical and spectral data confirm that the compound is 4-amino-3,5-dimethyl-1,2,4-triazole. The mass spectral fragmentation pattern has been successfully interpreted on the basis of its structure. 

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. 

A mass spectral study of 2-methyl-, 3-methyl- and 2,3-dimethyl-chromone (136), (137) and (138) has been reported (790MS345). In each case the molecular ion appears as the base peak, together with ions which correspond to [M-CO]-, [M-CHO]t, [RDA]t, [RDA + H]+ and [RDA-CO]t. Metastable peaks confirmed that the formation of [M-CHO]- occurs in two steps from [M]t. The reaction pathway for (136) and (138) is given in equation (2). In compound (137), [M-CHO]t is an abundant fragment ion (60%, cf. 35% for 136). That its generation occurs by more than one route is suggested not only by its high abundance, but also by the appearance of appropriate metastable ion peaks two pathways are operative (Scheme 17). 

Phenanthrene, fluoranthene, and pyrene—the three abundant parent PAHs identified by GC—were confirmed by MS. The major GC peaks between phenanthrene and fluoranthene were characterized as methyl- and dimethylphenanthrene/anthracene. Four compounds, each having a nominal mass of 192 amu were dejected. Small fragment ions at masses corresponding to (M-l), (M-27)+ and M", were detected. A general feature of these spectra was loss of a methyl group from the parent ion. The spectral features are characteristic of dimethyl or ethylphenanthrene/anthracene. 

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