Studies in organic mass spectrometry. I. — Acyclic 1, 3‐diketones

The mass spectra of 18 1, 3‐diketones are discussed. Next to the normal α‐cleavage of ketones, the most important fragmentations are the McLafferty rearrangement with the second carbonyl function in the ring, the expulsion of carbon monoxide and a specific σ‐cleavage of the side chain. The fragmentation seems to depend strongly on the enol content of the compound, enol molecules giving mainly α‐cleavage with loss of an alkyl radical, expulsion of carbon monoxide and σ‐cleavage of the side chain, while diketo‐molecules undergo in the first place the McLafferty rearrangement with the carbonyl function in the ring.