Protonation of halogen‐containing benzenes in HF‐SbF5. Part II.: PMR spectra of halotoluenium and halobenzenium ions

Abstract

AbstractA number of halotoluenes and halobenzenes have been found to give stable benzenium ions in HF‐SbF5. The PMR spectra of these ions are reported. A mixture of all three possible stable cations was obtained with m‐chloro‐ and m‐bromotoluenes; of m‐fluorotoluene only two cations were formed in observable amounts. Likewise, both possible stable m‐dichlorobenzenium ions were observed, but only one m‐difluorobenzenium ion. Reversible line broadenings in the spectra of all these ions, and of 1,3,5‐trichlorobenzenium ion showed the occurrence of rapid intramolecular and/or intermolecular hydrogen exchange reactions at temperatures of 0° C or lower, depending on the cation. In the cases of o‐chloro‐ and o‐fluorotoluenium ions fast exchange reactions lead to coalesced signals at temperatures as low as −40° and 0°, respectively. Protonated fluoro‐benzene and chlorobenzene likewise give coalesced signals at −40°.