INTRA-MOLECULAR RING-TO-RING PROTON-TRANSFER IN GASEOUS (OMEGA-PHENYLALKYL)BENZENIUM IONS

Gaseous (2-phenylethyl)benzenium and (3-phenyipropyl)benzenium ions 1 and 2 are generated easily by mass spectrometric loss of CO2H from the positive molecular ions of the corresponding 1-(w-phenylalkyl)-1,4-dihydrobenzoic acids 4 and 5. The major secondary fragmentation is loss of benzene from 1 and 2. It is shown by deuterium labeling that 1 and 2 ions undergo repeated ring-to-ring proton transfer reactions, equilibrating all of the 11 “aromatic” hydrogen atoms within ~10-5 is without involving those from the aliphatic chain. A competition between the ring-to-ring (quasi-iermolecular) proton transfer and proton shifts within the ring (“ring walks”) is discussed. © 1979, American Chemical Society. All rights reserved.