CO Loss from Carbonyl Compounds

A molecule of CO may also be eliminated from malonates, [132] P-keto esters, [133] phenoxyacetates, [134] and many other compounds containing similar structural features. 

Whatever the mechanism of CO loss might be, in none of the above cases CO loss proceeds by a simple bond cleavage. Instead, multistep rearrangements are necessary to cut the CO moiety out of the precursor ion. 

Note The detection of CO loss from molecular or fragment ions usually indicates the presence of carbonyl groups. However, it is less indicative of molecular structure than the highly specific reactions discussed before, because a multitude of rearrangement processes can be effective. These might even lead to CO loss in cases where no carbonyl group exists, e.g., from phenols. 

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