Dimethylated compound, mass spectrum

Dimethyl bromosuccinate was prepared from bromosuccinic acid by the diazomethane method (26) using the procedure of Eisenbraun, Morris, and Adolphen (27). It was distilled under vacuum (0.08-0.1 Torr) at 45°-49°C to yield a clear colorless oil. Thin layer chromatography with benzene as the solvent on SiC>2 yielded a symmetrical single spot, indicating either a pure compound or no separation with this particular solvent. Its mass spectrum had a very small peak corresponding to the parent compound, but none to a dibromo compound. The mass spectrum for dimethyl bromosuccinate was not found in the literature, but that for dimethyl succinate also has a small peak corresponding to the parent compound (25). 

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). 

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. 

Because no separation is used, only crude information about the purity of the compounds can be obtained. For example, if unreacted, synthetic starting materials (Fig. 10b) are present in a sample of a combinatorial product (Fig. 10a), these can show up in the mass spectrum of the crude product (Fig. 10c). Because the starting materials are often structurally different from the finished product, a simple extraction can be used after the synthesis to remove much of the unused reactants and obtain a cleaner mass spectrum (Fig. lOd) for a solution-phase product. Conversely, washing the resin after solid-phase synthesis or using a scavenger resin in a solution-phase synthesis can also yield improved purity by removing these excess reactants. When direct flow injection is used to characterize combinatorial libraries, it is best to avoid dimethyl sulfoxide (DMSO) as a solvent, because it interferes with reliable ionization of the analytes. 

A mass spectrum shows significant peaks atm/z = 87, 115, 140, and 143. Which of the following compounds is responsible for that mass spectrum 4,7-dimethyl-1-octanol, 2,6-dimethyl-4-octanol, or 2,2,4-trimethyl-4-heptanol ... 

Figure 5 El Mass Spectrum of Dimethylated Compound H from Geranium...

The IR and mass spectra are very similar for all four structures. The absence of dehydration in the mass spectrum indicates that the alcohol function at C-4 in the isohumulones is masked in the spiro-isohumulones. No fragment-ion is observed corresponding to the cleavage of the 4-methyl-3-pentenoyl group at C-4. The " h NMR data show that 81 and 82 belong to the trans series, while 83 and 84 are cis compounds. This follows from the complexity of the spectra (see 5.1.3.1.). Thus, at least two pairs of doublets are found for the geminal dimethyl groups of the... 

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