Reagent reorganization and promotive modes in barrier preparation for H-tunneling in fluorene–acridine system

For the hydrogen-atom transfer reaction in the fluorene–acridine system the set of two-dimensional potential energy surfaces (PESs) of the double adiabatic approximation type is examined on the PM3 semi-empirical level. The rate constant expression derived for this reaction is used to find the optimal atomic configuration of reagents, for which the potential energy barrier is minimal. The energy of reagent reorganization is also evaluated and its important role for describing this process is shown. The theoretical calculations of the rate constant are in agreement with the available experimental data, when the different promotive modes (translational, librational and two intramolecular) are taken into account.