Benzene ethyl, mass spectrum

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]+. 

Dry clean tanshen rhizomes were powdered and extracted with hexane for three days at room temperature. The hexane solution was kept overnight and then filtered. After removal of the solvent a residue was obtained which was separated into seven colored fractions by column chromatography with silica gel. Miltirone was isolated by preparative tic from fraction 1 (light red) using hexane ethyl acetate (4 1) followed by benzene-acetone (20 1). The product obtained was recrystallized from ethylacetate, m.p. 100-101°C. Its structure was confirmed by mass spectrum, NMR, IR and UV spectra which agree quite closely with those of Ho et al [76], Miltirone showed antioxidant behavior comparable to that of the commonly used phenolics BHT and BEA [77], The antioxidant activity of miltirone in lard at 100°C was determined with a Rancimat. Miltirone and other related compounds may have the potential of being used as natural antioxidants in food and cosmetics. 

The current mass spectral libraries (NIST 2002, Wiley 7) do not contain the spectra of these compounds, and therefore they were not identifiable by the MS library searches. The use of mass spectrum fragments can be of help in these situations. One example is the tentative identification for the peak with retention time of 75.48 min. (from Figure 6.9.2) as 4-methyl-1 - 1 -methyl-1 -[2-methyl-5-(methylethyl)cyclohexyl]ethyl benzene. The fragment assignments for the ions seen in the mass spectrum are shown in Figure 6.9.3. 

Figure 3. Partial mass spectrum of ethyl benzene...

Sanchez and Brown have obtained a new harman derivative from Aspi-dosperma exalatum Monachino (121). The alkaloid was obtained from a butanol extract, and in the IR spectrum it showed principal absorptions at 1925 cm-1 for an immonium ion, at 1610 cm-1 for a carboxylate anion, and at 748 cm-1 for a disubstituted benzene. In the mass spectrum a molecular ion was observed at m/e 226 and a base peak at m/e 182 (M+ —44). An aromatic methyl group and five aromatic protons were observed in the PMR spectrum. Consideration of this data together with the UV spectrum led to deduction of the structure of the alkaloid as 268, harman carboxylic acid. The ethyl ester (269) was also isolated but it was probably an artifact. 

Ethyl-lithium, though consisting basically of tetramer units associated into strips by tetramer-tetramer interactions in the crystal, both dissolves in hydrocarbons in hexameric form (EtLOe, and also vaporizes (from a study of its mass spectrum) as a mixture of tetramer and hexamer. The much-used reagent, -butyl-lithium, is also hexameric in hydrocarbon solution, but the structure of the hexamer is not definitely known. Menthyl-lithium is dimeric both in benzene and in cyclohexane, and this may well be connected with its considerably higher reactivity (e.g. to bromo-benzene) than, say, (Bu"Li)g. The state of lithium alkyls in donor (e.g. ether) solvents is mentioned at the end of this chapter. 

The mass spectra given in Figures 10.25 to 10.28 are those of benzene, methanol, ethanol, and methyl ethyl ketone. Tell which spectrum is of which compound, and justify your answers. 

Figure 20-1 illustrates how mass spectral data are usually presented. The analyte was ethyl benzene, which has a nominal molecular mass of 106 daltons (Da). To obtain this spectrum, ethyl benzene vapor was bombarded with a stream of electrons that led to the loss of an electron by the analyte and formation of the molecular ion M as shown by the reaction... 

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