Terpenoids, mass spectra

Classical natural products chemistry involved the isolation and purification of major natural product compounds from specific representatives of flora or fauna for structure determination. The terpenoids are the compounds of interest in this chapter and their initial structure elucidations were carried out in the 1930s—1970s. There are numerous compilations and encyclopaedia on terpenoids listing the physicochemical properties and literature background of the pure natural products. Many of the mass spectra of the underivatized terpenoid compounds are in the standard mass spectrum libraries of modern computerized data systems. 

Figure U. Top, APCI mass spectrum of rose oil vapors emanating from an open vial and bottom, MS/MS parent ion spectrum for 8l ions accentuating the terpenoid class of compounds in the...

A study to determine the absolute content of the volatile component of C. arietinum was conducted after the pod borer (H. armigera) was shown to be attracted to chickpea seed volatiles [14, 88]. GC-MS analysis of headspace material was collected from ground C. arietinum and identified 132 compounds from mass spectrum analysis retention times or Kovats indices (Table 1) along with a further 22 compounds which are not included here because their identities could not be confirmed [89]. The most abundant components were aliphatic hydrocarbons but the next most abundant class was the terpenoids constituting approximately 35% of the volatile fractions of the floured seed. The most abundant compound of all was a-pinene which comprised 12.6% of the total mass of volatile compound. The source of the many aliphatic hydrocarbons in this... 

MS and proton NMR spectroscopy have mainly been used for structure elucidation of isolated compounds. However, there are some reports on mass spectrometric analyses of essential oils. One example has been presented by Griitzmacher (1982). The depicted mass spectrum (Figure 2.9) of an essential oil exhibits some characteristic molecular ions of terpenoids with masses at miz 136, 148, 152, and 154. By the application of a double focusing mass spectrometer and special techniques analyzing the decay products of metastable ions, the components anethole, fenchone, borneol, and cineole could be identi ed, while the assignment of the mass 136 proved to be problematic. 

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