Monoterpenes, mass spectra

In addition, to actinidine (14), Janot and co-workers also isolated a new monoterpene alkaloid from the roots of Valeriana officinalis following treatment with ammonia (25). The isolate was analyzed for the formula Ci0H8N2O, and the UV spectrum showed maxima at 261,314, and 324 nm, and the IR spectrum a band at 1680 cm-1 for an aryl ketone. The mass spectrum displayed a molecular ion at m/z 172 with fragment ions at m/z 157 (M+-15) and 129 (MM3), suggesting the presence of a methyl ketone. A methyl singlet was observed at 2.65 ppm, and a complex pattern of five... 

M -CHiOH), 111 (24%, M -C3H7), 93 (17%, Nf.H2O-C3H7), 69 (90%, CsH9, and 41 (100%, 3115 ), indicative of a monoterpene alcohol. The con )ound was tentatively identified as the monoterpene alcohol lavandulol (1) by conq)arison with database spectra. The identification was verified with retention time matches on 3 GC capillary columns (DB-5, DB-17, and DB-WAX), and the mass spectrum matched t t of an authentic standard prepared by hydrolysis of commercial lavandulyl acetate (TCI America). 

The mass spectra of cycloalkenes show quite distinct molecular ion peaks. For many cycloalkenes, migration of bonds gives virtually identical mass spectra. Consequently, it may be impossible to locate the position of the double bond in a cycloalkene, particnlarly a cyclopentene or a cycloheptene. Cyclohexenes do have a characteristic fragmentation pattern that corresponds to a retro Diels-Alder reaction (Fig. 4.4). In the mass spectrum of the monoterpene Umonene (Fig. 4.16), the intense peak at m z = 68 corresponds to the diene fragment arising from the retro Diels-Alder fragmentation. 

On transfer of a proton from H3O+ to a VOC the dominant peak in the mass spectrum often arises from the protonated parent molecule. However, fragmentation may be significant for some compounds upon protonation, for example, monoterpenes, and In such cases a fragment ion is used as a marker for the particular compound(s). Where this occurs the fragment ion m/z has been provided in the table. 

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