THEORETICAL-STUDY OF REACTIVITY OF METHANE, METHYL-FLUORIDE, AND METHYL-CHLORIDE - INTERACTION WITH THEIR RADICAL CATIONS AND PROTON DONORS

This work deals with interactions between CH4 and CH4⋅+, CH3F and CH3F⋅+, and CH3Cl and CH3Cl⋅+. The calculated ΔH0 values (MP4/6-31G⋆⋆/MP2/6-31G⋆⋆, ZPE included) for processes leading to CH5+ and CH3⋅, and to CFH4 and CH2F⋅ amount to -1.8 and -21.0 kcal/mol, respectively. That ΔH0 leading to CClH4+ and CH2Cl⋅ (MP4/6-31G⋆⋆/SCF/6-31G⋆⋆, ZPE included) is -2.3 kcal/mol. The calculated reaction heat for the first interaction is significantly closer to experimental values (-4.16 and -6 kcal/mol, respectively) than our previous theoretical estimates. The structures of the radical cations (CH4⋅+, CH3F⋅+, CH3Cl⋅+) possess features of van der Waals associates. Methyl fluoride forms a weak hydrogen-bonded complex with HF the structure of which is, in contrast to expectation based on simple electrostatic consideration, nonlinear. The structure of the CH3Cl·HCl complex is analogous, but the ΔH0 value is very low (-0.1 kcal/mol). © 1990, American Chemical Society. All rights reserved.