Esters mass spectra

If the MW is not m/z 166 and there is an intense ion at m/z. 149, this suggests an ester of a benzene dicarboxylic acid. If m/z 149 is the most intense ion, the mass spectrum represents a phthalate, where R is an ethyl group or larger (see Figure 28.1). The most intense ions in the mass spectra of isophthalates and terephthalates are [M - OR]+. 

B. Method for determining the number of —COOH groups in a molecule The TMS derivative of an acid can be converted to the methyl ester using anhydrous methanolic HQ. 1 2 3 Obtain a mass spectrum of the TMS derivative of the acid, and then evaporate the TMS reaction mixture with clean, dry nitrogen. Add 250 pd of anhydrous methanolic HC1 (Pierce cat. no. 33050) and heat at 60° for 20 min. Many TMS derivatives of acids are converted to methyl esters at room temperature after 20 min. If the sample is rerun as the methyl ester, the number of carboxyl groups can be determined by the mass differences before and after making the methyl ester from the TMS derivative. 

Gas chromatographic analysis of the product showed two major peaks (relative intensity, 5 1), and the mass spectrum of each peak revealed a molecular ion at i/e 210. The proton magnetic resonance spectrum of the mixture showed that the two products were geometrically isomeric esters. 

Compound 37a showed the absence of an aldehydic proton and the singlet around 8.15 ppm was assigned to the ethylenic proton located p with respect to the electron-withdrawing cyano and ester groups. The benzofuranyl coumarins 38 exhibited the carbonyl-stretching band around 1690 cm in the IR spectra (Table 6). PMR data for 13 compounds are given in Table 2. The El mass spectrum of 36a showed a molecular ion peak at m/z 324 (41%). 

During a search for physiologically active compounds in South African plants, a new hasubanan ester acetal alkaloid, methylstephavanine (6), was isolated from Stephania abyssinica (19). The H-NMR spectrum of the new alkaloid 6 exhibited signals for one methylenedioxy, one N-methyl, and four methoxyl groups (19) (Table II). Its mass spectrum revealed the most abundant ion peak at m/z 229, indicating a close resemblance to the known hasubanan alkaloid, stephavanine (18). 

In order to be as fully confident as possible with this compound, given the two errors already apparent, it would be advisable to check it out thoroughly with HSQC, HMBC and a ROESY. This would establish the relative positions of the ethyl ester and methyl groups. A mass spectrum might be a good idea as well ... 

Japan wax does not contain any wax ester but only TAGs dominated by tripalmitin (T ).1 Its mass spectrum is thus very similar to that of this last compound with noticeable... 

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