DFT calculations show that the reaction between the pyrosulfate and alkanes to form carbocations is Ph3CH > 3 o C-H > 2 o C-H, which is expected based on the stabilities of these carbocations after hydride abstraction. The calculated energies also relate to the hydride ion affinity of the adsorbed SO3 site. Using the calculated gas-phase heterolytic C-H bond strengths for Ph3CH (191.5 kcal mol -1 ) 42 or the experimental value for the 2 o C-H in C3H6 (251.6 kcal mol -1 ) 43 brackets the hydride ion affinity of adsorbed SO3 between 226.2 to 237.9 kcal mol -1 . This value is larger than the calculated hydride ion affinity of Me3Si + (220.8 kcal mol -1 ) or SbF5 (127.4 kcal mol -1 ), the latter of which is generally accepted as the threshold for a Lewis superacid. From this analysis the SO3 site is, to our knowledge, the strongest formally neutral Lewis acid reported in the literature.