Ab Initio/IGLO/GIAO-MP2 Studies of Fluorocarbocations:  Experimental and Theoretical Investigation of the Cleavage Reaction of Trifluoroacetic Acid in Superacids¹a

The structures of a number of fluorocarbocations were calculated at the correlated MP2/6-31G* level. 13 C and 19 F NMR chemical shifts of fluorocarbocations were calculated for the first time using IGLO and GIAO-MP2 methods. The data showed good correlation of calculated 19 F and 13 C NMR chemical shifts with the experimental chemical shifts of fluorocarbocations. The correlation for GIAO-MP2-calculated 19 F NMR chemical shifts with the experimental data is excellent. Using theoretical calculations as guidance, the protolytic cleavage of trifluoroacetic acid (CF 3 COOH) in superacids forming CF 4 was also investigated experimentally and by ab initio calculations. This reaction is suggested to involve the gitonic CF 3 C(OH)(OH 2 ) 2+ dication as an intermediate.