Thermodynamic states, reaction generation

Using this representation, we can now focus on the identification of the associated thermodynamic states. We assess the likelihood of reactions as well as the inherent instability of each species associated with a node using LCR. The generation of infeasible species is limitated by the following values (i.e., knowledge) embedded in the corresponding attributes ... 

In the previous section we discussed how an inductive approach can be used to generate all the chemical reaction pathways and the associated thermodynamic states, which lead to top-level hazardous events. A potential hazard is said to exist when the thermodynamic state or sequence of thermodynamic states leading to the hazard cannot be prevented, or the... 

These reactions generate anion and cation exchange capacity on an iron oxide in this example. X and symbolize the anion and cation of the acid and base, where MX is an indifferent electrolyte. The chemical identity of the acid and base is lost upon reaction with the surface, but the exact chemical nature of the surface-bound ions need not be known to describe thermodynamically the equilibrium state of the oxide-electrolyte system. 

In a quasi-binary system, interdiffusion of ions also results in a so-called interdiffusion diffusion that is also rate-limited by the diffusivity of the slower of the two ions. This process occurs, e.g., when solid-state reactions between ceramics or ion-exchange experiments are carried out. Solid electrolytes can be used as sensors to measure thermodynamic data, such as activities and activity coefficients. The voltage generated across these solids is directly related to the activities of the electroactive species at each electrode. 

Studies of SET-induced excited-state reactions of phthalimides with a-trialkylsilyl substituted ethers, thioethers, and amines have shown that cation radical desilylation is the foundation of interesting photochemical reactions that proceed by pathways involving the generation and coupling of radical intermediates. In an early effort, we observed that simple, a-silyl-substituted ethers, thioethers, amines, and amides undergo efficient photoadditions to phthalimide and its N-methyl derivative. One example in this series of closely related reactions is the photoaddition of silylmethylpropylthioether 4 to N-methylphthalimide, which produces the product 5 (Scheme 4). In the mechanistic route for this process, thermodynamically/kinetically driven SET from 4 to the excited phthalimide leads to formation of the ion radical pair 6. Solvent (MeOH)-promoted desilylation of the cation radical and protonation of the phthalimide anion radical then provides radical pair 7, the direct precursor of adduct 5. 

Reactant and product structures. Because the transition state stmcture is normally different from but intermediate to those of the initial and final states, it is evident that the stmctures of the reactants and products should be known. One should, however, be aware of a possible source of misinterpretation. Suppose the products generated in the reaction of kinetic interest undergo conversion, on a time scale fast relative to the experimental manipulations, to thermodynamically more stable substances then the observed products will not be the actual products of the reaction. In this case the products are said to be under thermodynamic control rather than kinetic control. A possible example has been given in the earlier description of the reaction of hydroxide ion with ester, when it seems likely that the products are the carboxylic acid and the alkoxide ion, which, however, are transformed in accordance with the relative acidities of carboxylic acids and alcohols into the isolated products of carboxylate salt and alcohol. 

No single mechanism accounts for all the reactions. One pathway involves a concerted one-step process involving a cyclic transition state. This of necessity affords a c -product. Another possibility, more favoured in polar solvents, involves a cationic 5-coordinate intermediate [IrX(A)(CO)L2]+, which undergoes subsequent nucleophilic attack by B-. Other possibilities include a SN2 route, where the metal polarizes AB before generating the nucleophile, and radical routes. Studies are complicated by the fact that the thermodynamically more stable isolated product may not be the same as the kinetic product formed by initial addition. 

---