Abstract
The mass spectrum of tropylium fluoroborate (C7H7+BF4) shows a base peak corresponding to the cationic portion of the salt (m/e91) and intense peaks occur at m/e 109 (C7H6F+) and m/e 110 (C7H7F+.). The latter peaks are probably of thermal origin. A similar rearrangement is observed in trityl fluoroborate (C19H15+BF4) and may be a general feature of the mass spectra of aromatic fluoroborates.