The mass spectra of some naturally occurring and synthetic a- and ?-pyrones, benzofurans, and 2,2-dimethylchromenes have been determined. Under electron impact compounds derived from coumarin lose oxygen atoms as CO, usually forming a stable benzofuran ion. 2,2-Dimethylchromenes lose a methyl radical to give a stable benzopyrylium ion, while the most prominent fission of flavanoid compounds occurs by breaking both bonds ß to the A ring.
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Barnes et al. (1964) studied this question.