Born-Oppenheimer direct dynamics classical trajectory simulations of biomolecular collisions of PETN molecules have been performed to investigate the fundamental mechanisms of hypervelocity chemistry relevant to initiating reactions immediately behind the shock wavefront in energetic molecular crystals. The solidstate environment specifies the initial orientations of colliding molecules. The threshold velocities for initiating chemistry for a variety of crystallographic orientations were correlated with available experimental data oil anisotropic shock sensitivity of PETN. Collisions normal to the planes (001) and (110) were found to be most sensitive with threshold velocities oil the order of characteristic particle velocities in detonating PETN. The production of NO2 is the dominant reaction pathway in most of the reactive cases. The simulations show that the reactive chemistry, driven by dynamics rather than temperature during hypervelocity collisions, can occur at a very short time scale (10-(13) s) under highly nonequilibrium conditions.