A phenomenon showing up both in the butane and cyclohexane reaction systems, is the OH-shift isomerization, a pathway also noted by Green et al. 52 in their QO 2 H --→ HOQO isomerization study. In MD simulations, atoms are in constant vibration, especially lighter atoms like H atom or groups like OH with less inertia. This results in a strong tendency to drift away either as a free radical or to other radical sites. Also due to the low barrier at the ReaxFF level (< 10 kcal mol -1 ), reactions like H-or OH-shifts were frequently observed.