The gas-phase reactivity of methyl fluoride with selected first-row transition metal monocations (Sc+, Ti+, V+, and Zn+) has been theoretically investigated. Our thermochemical and kinetics study shows that early transition-metal cations exhibit a much more active chemistry than the latest transition metal monocation Zn+. The strong C-F bond in methyl fluorine can be activated by scandium, titanium, and vanadium monocations yielding the metal fluorine cation, MP+. However, the rate efficiencies vary dramatically along the period 0.73 (Sc), 0.91 (Ti), and 0.028 (V) in agreement with the experimental observation. The kinetics results show the relative importance of the entrance and exit channels, apart from the "inner" bottleneck, to control the global rate constant of these reactions. At the mPW1K/QZVPP level our computed k(global) (at 295 K), 1.99 X 10(-9) cm(3) molecule" s(-1) (Sc+), 1.29 x 10(-9) cm(3) molecule(-1) s(-1) (Ti+), and 3.46 x 10(-10) cm(3) molecule(-1) s(-1) (V+) are in good agreement with the experimental data at the same temperature. For the reaction of Zn+ and CH3F our predicted value for k(outer), at 295 K, 3.79 x 10(-9) cm(3) molecule(-1) s(-1), is in accordance with the capture rate constant. Our study suggests that consideration of the lowest excited states for Ti+ and v(+) is mandatory to reach agreement between calculations and experimental measurements.