Stability acceleration effect

Succinic anhydride is stabilized against the deteriorative effects of heat by the addition of small amounts (0.5 wt %) of boric acid (27), the presence of which also decreases the formation of the dilactone of gamma ketopimelic acid (28). Compared with argon, CO2 has an inhibiting effect on the thermal decomposition of succinic acid, whereas air has an accelerating effect (29,30). 

Conjugated substituents at C-2, C-3, C-4, or C-5 accelerate the rearrangement. Donor substituents at C-2 and C-3 have an accelerating effect. The effect of substituents can be rationalized in terms of the stabilization of the transition state by depicting their effect on two interacting allyl systems. 

Ralph Pearson I would like to go back a couple of questioners and answer Dr. Halpern s question. I wrould certainly like to believe that the accelerating effect of the hydroxyl group is caused by ir-bonding s stabilizing a five-coordinated intermediate wdth a trigonal bipyrimidal structure. 

For foams of low stability the effect of the different factors on foam expansion ratio is difficult to anticipate, since the accelerated internal collapse and the partial destruction of the foam column during foaming lead to an increase in the amount of excess liquid in the foam, to bubble expansion and to increase in surfactant concentration that also affect the rate of drainage. 

Boric oxide seems to be an exception in that it has a remarkable accelerating effect on the rate. It reduces the first limit to almost unobsorvably low pressures and causes the third limit to become very violent. This seems to be related to the known stability of 11202 in B2OS, and Warren ascribes the effects to th(i lack of efficiency of the surface for destroying IIO2. In view of the fast reaction produced at the first limit, it seems more likely that B2O3 is an effective catalyst for the production of HO2 from H2 + O2. 

This simple approach neglects the influence of geometrical differences in the phosphoryl group in the ground state and transition state, which have been shown to have the potential to result in preferential enzymatic stabilization of a loose, metaphosphate-like transition state.26,27 While there have been many reports of the accelerating effect of metal ions on phosphoester hydrolysis,28 31 few of these reactions have been studied mechanistically to ascertain how the transition state for phosphoryl transfer might have been affected. 

The stabilization of the carbocation intermediate 35 by the isobutylidene group must be a driving force to promote the reaction. The striking feature in the cyclization is a remarkable acceleration effect by the fluorine substituent at the same carbon. The fluorine substituent gives an excellent rate of acceleration and product yield. In contrast, the SnCU-catalyzed cyclization of nonsubstituted polyolefin 34 (R = H) in hexane gives only 30% of the cyclized product in 20 min. 

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