Nuclear Quantum Effects\non the Nature of Hydroboration\nSelectivity: Experimental Effects of First-Collision Tunneling

The understanding of selectivity in reactions exhibiting\nnonstatistical\ndynamics is impeded by the limitations of trajectory studies with\nregard to nuclear quantum effects, especially tunneling. We described\nhere the use of ring-polymer molecular dynamics (RPMD) to account\nfor an unusual regiochemical isotope effect on the regioselectivity\nof hydroborations of alkenes with BH<sub>3</sub>/BD<sub>3</sub>. RPMD\nis able to account for the experimental observation, while statistical\napproaches and classical trajectories fail. The combination of experiment\nand RPMD trajectories suggests that tunneling in the initial collision\nof reactants is the major source of the nonstatistical selectivity.