Dimer acid structures. The thermal dimer of normal linoleate, methyl 9‐cis, 12‐cis octadecadienoate

The thermal dimer (290C) of normal methyl linoleate and its hydrogenated form have been examined by mass spectrometry. Parent mass peaks of the hydrogenated dimer show the presence of monocyclic, bicyclic, and tricyclic structures. The monocyclic structure is formed via the conjugation‐Diels‐Alder mechanism. The bicyclic structure is best explained by an extension of the hydrogen transfer free radical coupling mechanism. The noncyclic dehydrodimer resulting from free radical coupling undergoes a relatively rapid intramolecular cyclization to a bicyclic structure, probably by an interval Diels‐Alder reaction. A model noncyclic dehydro‐linoleate dimer was shown to give a bicyclic dimer as the predominant structure under thermal dimerization conditions. The tricyclic dimer may result from intramolecular alkylation of the bicyclic structures.