Dimethylated, mass spectral

In order to characterise the components further, mass spectral analysis was carried out. When head space volatiles from undigested cow slurry were analysed on a non-polar column the results (Figure 5) demonstrated the presence of several sulphur containing compounds—methanethiol, carbon disulphide, dimethyl sulphide, 2-propanethiol,... 

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). 

The various tautomers and rotamers of alloxan have been examined in detail by the MNDO method and it is predicted that the keto form is most important in the gas phase, although in solution the monohydroxy forms are also thought to contribute. A mass spectral study has been used to investigate the enol-keto tautomeric equilibria of a series of substituted salicylaldehyde and 2-hydroxynaphthaldehyde Schiff bases. In neutral, ethanolic solutions, the cis- and trans-tm forms of 4,5-dimethyl-2-(2 -hydroxyphenyl)imidazoles (393) and (394) have been found to exist in equilibrium in the ground state. However, in neutral aqueous solutions, the trans-eao and keto forms (394) and (395) were the only species detected. Deuterium isotope effects on... 

Dimethylamine (109), putrescine (111), and spermidine (110), isolated from various insects (Table VIII), were obtained as p,p -nitrophenylazobenzoyl, p-phenylazobenzenesulfonyl, and I-dimethylaminonaphthalene-5-sulfonyl (dan-syl) derivatives and picrates or were detected by high-performance liquid chromatography (HPLC) using the ion-exchange resin (106,343). V,V-Dimethyl-3-phenylethylamine (131) from spiders of the genus Sclerobunus (Table VIII) has been identified by mass spectral comparison with a synthetic sample (117). 

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). 

Alkylphosphines have been studied (99, 231), as have cyclopolyphos-phines (120). The reaction products of phosphorus with various olefins were investigated using mass spectral methods (108), and a large number of phospholines have been reported (181, 237). The mass spectrum of the trimer of tetramethylphosphinoborine showed that B—P, C—B, and C—P bonds were broken first, and with the pentamer of the dimethyl compound, B—H, B—P, and C—P bonds were broken (101, 232). The spectra of thiophosphorustri-A -methylimide and its arsenic analog were reported by Holmes and Forstner (130). Ionization potentials have been recorded for many perfluoroalkylarsines and some of the related alkyl compounds (79). 

Two cytotoxic spermidine derivatives were isolated as a mixture from the Pacific soft coral Sinularia brongersmai 5,12-dimethyl-1-dimethylamino-5,9-diazaheneicos-l l-en-10-one (35) and its 11,12-dihydroderivative 36 (ratio 9 1). By hydrogenation of the mixture, a single compound was obtained that corresponded by GC/MS analysis to the minor component of the original mixture. Hydrolysis followed by esterification of the hydrogenated product 36 afforded methyl 3-methyldodecanoate and N,N,N-tri-methylspermidine. The results of a Hofmann degradation of 36 confirmed the conclusion on mass spectral evidence that the primary amide nitrogen is bonded to the trimethylene chain of the unsymmetrical spermidine molecule (61). 

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

A number of papers concerned with the decomposition behaviour of organic halogen compounds in the mass spectrometer and related systems is to be found in the journal Organic Mass Spectrometry. For example, in the case of fluoro-compounds, McCarthy has discussed mass spectral correlations for fluorinated alkanes studies by other workers have included those on aromatic fluoro-com-pounds , fluorine-containing dimethyl esters , and tetrafluoroethanes . In the same journal, studies on other halogen compounds include dichlorocyclo-propanes , norbornyl chlorides and bromides , j8-phenylethyl bromides , and chloro-substituted benzynes . 

Some of the peak assignments in Tabie 6.7.20 are tentative because the mass spectra of many compounds in poiy(methyi methacrylate) pyrolysate are not available in the commercial mass spectral libraries. For example, 2-methylene-4,4-dimethyl-pentanedioic acid dimethyl ester (MW = 200) and 2,4,4 frimethyl-2-pentenedioic acid dimethyl ester (MW = 200) were assigned based on the mass spectra shovm in Figures 6.7.28 a and 6.7.28 b. 

Figure 6.7.29. Spectrum of 2-methyl-3-methylenehexanedioic acid dimethyl ester (from NIST 98 mass spectral library).

On the other hand, the spectrum of [(2-methylphenoxy)-1,2-dimethyl]oxirane is not available in common mass spectral libraries. The mass spectrum of the peak eluting at 84.07 min. in the pyrogram shown in Figure 8.3.3 is given in Figure 8.3.5 and was assigned to this compound by comparison with its next lower homolog. 

Pyrolysis of poly(2,6-dimethyl-1,4-phenylene oxide) [-C6H2(CH3)20-]n, CAS 25134-01-4, is further discussed for a sample with M = 244,000. The experimental conditions used to generate the pyrogram shown in Figure 9.1.17 were similar to those for other previous examples (see Table 4.2.2). Peak identification for the pyrogram was done using mass spectral library searches only and is given in Table 9.1.10 and Table 9.1.11. 

I.r. and mass spectral data show that an intermediate in the production of 2,5-dimethyl-1,3,4-trioxadiborolan by the reaction of Me2BH2BH2 + 02 is Me2BOOH (dimethylboryl hydroperoxide).215... 

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>. 

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