MD based free energy calculations do not rely on any models for the canonical partition functions. Table : Total energy barrier, (∆E ‡ ), entropy contribution (∆S ‡ ), free energy barrier (∆F ‡ = ∆E ‡ -T ∆S ‡ ) for R → P at 300 K computed using structure optimization, followed by thermochemistry computations for the optimized structure using model partition functions. Free energy barriers computed from TASS are also listed for a comparison. Here energies are in kcal mol -1