The Loss of CH3COCH2 Moieties from Methylketo Esters upon Electron Impact: A discussion of possible long‐range functional group interaction

Methyl 10‐oxoundecanoate and related long‐chain methylketo esters exhibit loss of the terminal CH3COCH2 moiety as one of the most prominent modes of fragmentation in analogy to comparable long‐chain diketones. In view of its absence in simple monoketonic analogues this process is thought to be induced by the distant ester function, e.g. via hydrogen abstraction from a suitable site (C(7)) within the alkyl portion of the molecule to be retained in the fragment. Rearrangement indicative of functional group interaction is thus concealed, and the attempt is made to unravel its incidence and true course by analysis of the further decomposition of the (M‐CH3COCH2) fragment via sequential losses of MeOH and CO, with the emphasis on establishing the origin of the OH hydrogen of the former of these two particles. Extensive deuterium labelling of most of the positions of the central chain, as well as analysis of pertinent high‐resolution data and metastable transitions, is employed in the pursuit of this objective.