Studies on Long-Lived (Pentafluorosulfanyl)phenyl-Substituted Carbocations.

A variety of long-lived carbocations containing the p-(pentafluorosulfanyl)phenyl and m-(pentafluorosulfanyl)phenyl groups have been characterized by low-temperature NMR spectroscopy. In the case of potential nonclassical carbocations substituted with the p-(pentafluorosulfanyl)phenyl substituent, deviations from linearity when the Hammett parameter (σC+) is plotted versus 13C NMR shifts of the carbocationic center were observed. Plotting the experimentally derived 13C NMR shifts versus σC+ or σ+ of classical 4-phenyl-X substituted carbocations also provides a means to accurately back-calculate the σ+ and σC+ parameters of the -SF5 substituent.