The molecular ion peak is usually only observable in methyl esters.
An important fragmentation pattern involves a-cleavage (breaking either bond to the carbonyl carbon). Loss of the alkoxy group is the most important of these fragmentations as shown in figure 40.
Figure 40. a-cleavage.
McLafferty rearrangement can take place for esters in the alkyl portion (see figure 41).
Figure 41. McLafferty rearrangement of an ester.
The complete mass spectrum for ethyl acetate is given in figure 42, which illustrates most of these points.
Figure 42. Mass spectrum for ethyl acetate.
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