Product-favored change

Product-favored change A change for which the collection of products is more stable than the collection of reactants under the given conditions also called spontaneous change. 

Reduction of tri-(2-thienyl)methyl carbenium tetrafluoroborate by zinc in DME at 65°C produces, via the radical (341), two dimers (342) and (343). The former is the kinetically favored product, which changes to the thermodynamically preferred (343) on thermal equilibration. This obviously takes place by dissociation into the radical (341) (90TL2627). 

O-Methylation of the optical isomers of THP gave only little of the desired norreticulines (Fig. 30) and mostly products which were methylated at the hydroxy groups at C-7 and C-3. Whether the proportion of methylated products would change in favor of those representing norreticulines if COMT of a different origin were to be used, or if THP would be chemically modified at the NH group (N-CHj, N-acyl) is not known. 

When A// and AS have opposite signs (classes 1 and 4), they act in the same direction, so the direction of spontaneous change does not depend on temperature. When Aff and AS have the same signs (classes 2 and 3), their effects oppose one another, so changes in temperature can cause one factor or the other to dominate, and spontaneity depends on temperature. For class 2, decreasing the temperature decreases the importance of the ur a-vorable T AS term, so the reaction becomes product-favored at lower temperatures. For class 3, increasing the temperature increases the importance of the favorable T AS term, so the reaction becomes product-favored at higher temperatures. 

If the changes are Implemented in the Delaney clause then the door could be opened to the registration of a number of new products. The products favorably affected by changes in the policy would be those that are positive in animal carcinogenicity studies, but are either of very low potency, or caused tumors considered less relevant to human risk. The Delaney clause would not increase the chances of registering a product that appeared to pose a significant risk by dietary exposure. 

Gibbs free energy change, AG The indicator of spontaneity of a process at constant T and P. AG = AH — T AS. If AG is negative, the process is product-favored (spontaneous). 

Two ways of predicting reaction direction are from the vaiue of AG and from the relation of Q to K. These variabies represent different aspects of the same phenomenon and are reiated to each other by AG = RT in Q/K. When Q = K, the system can reiease no more free energy. Beginning with Q at the standard state, the free energy change is AG°, and it is reiated to the equiiibrium constant by AG° = -RT In K. For nonstandard conditions, AG has two components AG° and RT in Q. Any nonequilibrium mixture of reactants and products moves spontaneousiy (AG < 0) toward the equiiibrium mixture. A product-favored reaction has K > 1 and, thus, AG° < 0. 

The allergenic character of cow s milk casein, its EPM products with and without methionine enrichment, and the two fractions (selected by FPLC) of the Met-enriched EPM product were also investigated (Fig. 3). The allergenic character of the enzymatically modified products of cow s milk casein shows favorable changes the allergen-... 

---