Energy barriers
In a subsequent step we have computed both the structures and energies of the transition states for the formation of the adducts in the solvents. Table 4 gives the relative Gibbs free energy for the transition structures computed for the direct reaction (in this case the values are computed relative to the reagents) and for the reverse reaction (in this case the values are computed relative to the adducts). The existence of a barrier for the direct reaction is highly dependent on the solvent. Solvents with higher dielectric constant, water in this case, may induce an activation barrier.
Table 4. Gibbs free energy activation barrier to the direct and reverse reactions (in kcal mol-1).