Determination and characterization of cyclodimers of naturally occurring phenolic acids

The phenylpropenoic acids, cinnamic, p-coumaric, ferulic, sinapic and caffeic, were photodimerized either singly or in pairs and were subjected to gas chromatographic and mass spectrometric analyses of their trimethylsilyl derivatives. Sinapic acid and five combinations of pairs gave only a single peak when analysed on two gas chromatographic columns, while all the rest gave two peaks. Mass spectrometric analysis showed that, for most combinations, a dimer in the head-to-tail configuration was the major product but significant amounts of some dimers in the head-to-head configuration were produced. For most dimers, the molecular ion was evident in the spectrum while the configuration of the cyclobutane ring was established by the fragments formed from symmetrical and asymmetrical splitting.