Mass spectral fragmentation ketones

An example of how information from fragmentation patterns can be used to solve structural problems is given in Worked Example 12.1. This example is a simple one, but the principles used are broadly applicable for organic structure determination by mass spectrometry. We ll see in the next section and in later chapters that specific functional groups, such as alcohols, ketones, aldehydes, and amines, show specific kinds of mass spectral fragmentations that can be interpreted to provide structural information. 

Different methods of computer-matching the mass spectra of 122 monoterpenoids give the best results when six to eight of the most intense peaks are matched.21 The mass spectral fragmentation patterns of various bicyclic ketones of the thujane and carane series, and of their deuteriated [e.g. (6 X = D)] analogues, did not produce any generalizations on the fragmentation patterns or on the deuterium content.22... 

Several 21,22-seco-diacids (150) have been prepared in the 20/S,28-epoxy-18a,19/8H-ursane series by oxidation of the corresponding 22-hydroxymethylene-21-ketones (151). Reaction of the 21-ketone (152) with oxygen in an alkaline medium afforded the a-hydroxy-acid (153) and the seco-diacid (150). ° Several interesting reactions were observed during this work. ° While pyrolysis of the a-acetoxy-acid (154) yielded the ketone (155) pyrolysis of the seco-diacid anhydride resulted in loss of carbon monoxide and formation of the lactone (156). Lead tetra-acetate oxidation of the ketone (155) [or the hydroxy-acid (153)] followed a Baeyer-Villiger pathway to the lactone (156). The ketone (155) was very susceptible to reduction in the presence of alcoholic alkali. The mass spectral fragmentation of a series of compounds based on 20/8,28-epoxy-18a,19/8H-ursane has been examined. ... 

The localisation of hydroxy-groups from study of mass spectra of the derived ketones has been described. 5a- and 5 -3-oxo-steroids can generally be distinguished by their characteristic fragmentations. The same compounds can be converted into their enol trimethylsilyl ethers, having the olefinic bond respectively in the A - and A -positions. Each affords a distinctive mass spectral fragmentation pattern. ... 

We ll see in the next section and in later chapters that specific fiinctional groups, such as alcohols, ketones, aldehydes, and amines, show specific kinds of mass spectral fragmentations that can be interpreted to provide structural information. 

Mass spectral fragmentation of aldehydes and ketones provides structural information... 

CH3-C0-C=CH2 and >CH-CH20H follow from n.m.r. and i.r. spectra, that of the two AT-methyl groups from n.m.r. The constitution follows from the mass spectral decomposition which involves two principal fragmentation modes which are shown in Scheme 14. This scheme is supported by, amongst other things, examination of the spectra of 20,21-dihydromacroline (catalytic hydrogenation product), the so-called macralinol (ketone function reduced with lithium aluminium hydride), and structurally related derivatives of ajmaline. ... 

The NO+ ion, an ionic reagent often used in SIFT-MS instrument, is used to distinguish several isobaric aldehydes and ketones. The ionic reaction of NO tends to lead to more fragmentation and the formation of complex that provides a specific mass spectral characteristics to discriminate between aldehyde and ketone molecules [8]. 

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