Transition State Structure For Hydrogen Abstraction From Methane by Fluorine

The transition state structure is shown for the hydrogen abstraction from methane by fluorine radical. The length of the C-H bond that is being broken is 115.3 pm while the other three C-H bonds are 108.7 pm long. The H-F distance is 135.0 pm long in the transition state and it is 93.4 pm in HF itself. The H-C-H(F) angle is 106.7 degrees and remains close to the tetrahedral angle. Hence: This transition state is EARLY. The structure looks very much like the structure of methane, the HF bond is not formed yet to any significant extent, and the methyl radical is not yet developed significantly. The early transition state is expected since the activation energy for the reaction is low, 1.2 kcal/mol, and the reaction is exothermic.

Figure. The UMP2(full)/6-31G* optimized structure of the transition state structure for
hydrogen abstraction reaction from methane by fluorine.