were assumed to have very high activation energies. The
reactions (4) are not even considered in chemical kinetics
and physical chemistry [5–7]. However, more recently, some
researchers suggested the substitution reaction can play a
significant role in the complex chemical processes, for
example, in combustion and pyrolysis [8–12]. These
reactions should be considered when interpreting the results
of mechanistic studies of complex processes. In this article,
the competition of the substitution reaction (3) with the
abstraction reactions (1) and (2) is considered for the
reactions CH3XCH (XZF, Cl, Br).