The structure of the product ion of a ‘McLafferty’ rearrangement

A series of alkylphenylketones has been examined. Whenever the alkyl chain is three or more carbon atoms long, the well‐known McLafferty rearrangement occurs with elimination of the elements of a neutral olefin. The further fragmentation of the ion formed in this rearrangement reaction has been studied using the technique of ion kinetic energy (IKE) spectroscopy. The measured release of kinetic energy has been used to show that the rearrangement ion has an enolic type structure.