Superacid chemistry in the gas phase: dissociative proton attachment to halomethanes

The standard Gibbs energy changes for the halide transfer processes in the gas phase have been determined by means of Fourier transform ion cyclotron resonance mass spectrometry (FT ICR): 1 - Ad - X(g) + R+ (g) --> 1 - Ad(+) (g) + R - X(g) X = Halogen; 1-Ad = 1-Adamantyl; R-X = CCl4 (1), CBr4 (2), CI4 (3) and CBr3F (4). To this end, systematic use was made of the dissociative proton attachment method (DPA) [J-L.M. Abboud et al., J. Am. Chem. Sec. 116 (1994) 2486-2492.], which allowed one to experimentally determine the onsets for reactions: R - X(g) + BH+ (g) --> R+ (g) + HX(g) + B(g) R = CCl3, CBr3, CI3, CBr2F, 1-Ad. In the case of 4, two different onsets were determined, respectively, corresponding to the formation of CBr2F+(g) and CBr3+ (g). The thermodynamics of several reactions (see the first equation above) were studied at the MP2/6-31G(d) level. The results agree very satisfactorily with the experimental results. (C) 1998 Published by Elsevier Science B.V. All rights reserved.