Transition State Structure For Hydrogen Abstraction From Methane by Chlorine

The transition state structure is shown for the hydrogen abstraction from methane by chlorine radical. The length of the C-H bond that is being broken is 143.8 pm while the other three C-H bonds are 108.4 pm long. The H-Cl distance is 143.1 pm long in the transition state and it is 128.0 pm long in H-Cl itself. The H-C-H(Cl) angle is 101.2 degrees and it is significantly less than the tetrahedral angle. Hence: This transition state is LATE. The structure no longer looks like methane but the development of a methyl radical is clearly indicated and the H-Cl bond is being formed. The activation barrier for this reaction is 4 kcal/mol.

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