Ping-Pong Reactions by Heavy Atom Tunneling

Quantum mechanical tunneling (QMT) is a known effect that has the potential to significantly accelerate the kinetics of chemical reactions even at extremely low temperatures, where classical, “over the barrier” thermal reactions are virtually impossible. Since this effect is dependent on the mass of the shifting atoms, QMT has been widely studied for hydrogen transfer. However, a slowly growing body of evidence has shown that “heavy” (i.e. non-hydrogen) atom tunneling is indeed possible, as long as the barrier height is low and, more important, the barrier width is markedly narrow. In this computational research degenerate rearrangement reactions of the “Ping-Pong” style have been studied, where a heavy atom (fluoride or boron) jumps from one conformation to another over an anthracene or similar scaffold. These reactions possess a double-well potential energy surface where the atomic trajectory to pass from one minimum to another is extremely short, and the barrier height is too high to be traversed via a classical thermal pathway at low temperatures, thus making these reactions ideal for QMT.