The molecular ion peak is quite intense.
Fragmentation patterns mimic those of the aldehydes. a-cleavage in ketones favors the loss of the larger alkyl group as shown in figure 36.
Figure 36. a-cleavage.
McLafferty rearrangement can take place for ketones with at least 3 carbons (see figure 37).
Figure 37. McLafferty rearrangement of a ketone.
For aromatic ketones, a-cleavage usually occurs, which is followed by loss of carbon monoxide as indicated in figure 38.
Figure 38. Aromatic ketone fragmentation.
The complete mass spectrum for 2-pentanone is given in figure 39, which illustrates most of these points.
Figure 39. Mass spectrum for 2-pentanone.
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