The reactions of CH3+, CH2Cl+ and CHCl2+ with standard reference bases were examined in a dual cell Fourier transform mass spectrometer. Deprotonation of methyl cation occurs rapidly via a spin forbidden process to afford triplet methylene even when the reaction is nearly thermoneutral. Bracketing results enable us to assign PA(CHCl) = 209.7 ± 2.2 kcal mol-1 and PA(CCl2) = 205.2 ± 1.9 kcal mol-1, the latter value of which is considerably larger than previous determinations. The resulting heats of formation, however, are in good accord with other measurements and lead to recommended values of Δ Hf °(CHCl) = 74.6 ± 2.4 kcal mol-1 and Δ Hf °(CCl2) = 53.0 ± 2.6 kcal mol-1. These values correspond to a 2-3 kcal mol-1 lowering of these quantities and are within 1-2 kcal mol-1 of high level G3 and W1 predictions based upon the atomization energies and a series of four isodesmic reactions.
Bibliographical noteFunding Information:
Support from the National Science Foundation, the donors of the Petroleum Research Foundation, as administered by the American Chemical Society and the Minnesota Supercomputer Institute are gratefully acknowledged.
Copyright 2007 Elsevier B.V., All rights reserved.
- Methyl cation
- Spin-forbidden reaction