Hydroxylation barrier height

In order to overcome the reaction barrier within current restrictions of computer time, the hydrogen coordination number of the hydroxylic oxygen was forced to decrease from unity to zero by applying a suitable constraint [47, 88, 89], By thermodynamic integration it is possible to determine the free energy barrier height for this process [19]. 

The barrier heights for the CH3 addition to the hydroxyl ligand calculated relative to the intermediate IV 9 and IV 11 are 9.3 and 7.3 kcal/mol for the "A and "A states, respectively. Obviously, this step of the reaction is not rate-determining, and can occur rather fast. Overcoming the barriers at TS2 leads to the complexes methanol-complexes VI, L4Fe(0HCH3)(p-0)FeL4, and completes... 

To understand the correlation between sulfoxidation barrier height and ionization potential of the substrate, also here a VB curve-crossing diagram was set up (106), which is shown in Fig. 13. In contrast to aliphatic hydroxylation and epoxidation discussed above, the sulfoxidation reaction is concerted without a reaction intermediate. Therefore, the reactants connect with products directly and the promotion gap as a result reflects the excitation energy from the reactant wave function to the product wave fimc-tion in the reactant geometry. The excited wave fimction Fp essentially refers to the one-electron transfer from substrate to oxidant hence it is proportional to the IE of the substrate and the electron affinity of the oxidant. Consequently, the correlation... 

Thanks to newly evolved experimental possibilities of generating solvated ions in gas phase, the rates of the gas-phase reactions of Eq. (5.6) could be determined for various degrees of the hydroxyl anion hydration [54]. The calculations [53] have shown a substantial rise of the barrier height AE -h AE in Fig. 5.2) with the increase in the degree of anion hydration in Eq. (5.5), which explains the observed fall by four orders of magnitude in the rate of the analogous reaction of Eq. (5.6) upon passing from the unhydrated hydroxyl anion (n = 0) to the hydrate u = 3. 

Figure 22.22 CO reaction mechanisms as determined by impedance measurements. In the low CO concentration range, the reaction with hydroxyl groups is dominant. The corresponding decrease in the dielectric constant s results in a decrease in the CPE value. For higher CO concentrations CO reacts predominantly with oxygen. The increase in CPE is related to the decrease in the potential barrier height with increasing CO concentration [22]...

Fig. 19. Catalytic effect of neutral salt on the alkaline hydrolysis of monocetyl succinate ions, Ci6H330-C0-CH2-CH2-CO2 . The monolayer bears a net negative electrical charge. This repels the similarly charged hydrolytic hydroxyl ions. The height of this electrical repulsive barrier is reduced greatly by any neutral salts (Davies and Rideal, 21).

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