Spectroscopy of Stable C7H7+

Spectroscopy of Stable C7H7+

Author: Angewandte Chemie International Edition

The electronic spectroscopy of the two most stable C7H7+ species has now been studied in detail thanks to the efforts of John Maier and his team from the University of Basel, Switzerland. Electronic absorption spectra of benzylium (Bz+; see picture) and tropylium (Tr+) cations were recorded after mass-selected trapping of the cations into a neon matrix. Measurements in different regions of the spectra revealed both weak and strong transitions for Bz+ (C2v), along with the lowest dipole-allowed transition for Tr+ (D7h). Density functional calculations were performed to support interpretations of the ground-state energy and vibrational frequencies of Bz+ and Tr+.

Physical organic chemists have been debating the mass spectrometry and spectroscopic data with respect to the formation and automerization pathways of Bz+ and Tr+, for a long time. The spectroscopic information from this study should provide a reliable starting point for further gas-phase detection and investigation of benzylium and tropylium cations.


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