Given the high flexibility of the molecules under investigation, conformational analysis for minima and transition states is performed with CREST program in order to provide starting guesses for the potential energy surfaces calculations. The code couples state-ofart semiempirical quantum chemical methods (GFNn-xTB) with metadynamics simulations . All geometry optimizations as well as energy, thermodynamic functions and frequency calculations have been performed using the Gaussian code . Rate coefficients are determined by the conventional transition state theory (TST) within the rigid-rotor harmonicoscillator (RRHO) approximation, and they can be expressed by