Stability results

FIGURE 10 6 Confor mations and electron delo calization in 1 3 butadiene The s CIS and the s trans con formations permit the 2p or bitalsto be aligned parallel to one another for maxi mum TT electron delocaliza tion The s trans conformation is more stable than the s CIS Stabilization resulting from tt electron de localization is least in the perpendicular conformation which IS a transition state for rotation about the C 2—C 3 single bond The green and yellow colors are meant to differentiate the orbitals and do not indicate their phases... 

Table 1.13. Calculated Stabilization Resulting from Substituents on the Methyl Cation...

Estimated stabilization resulting from conjugation in kcal/mol. 

Radicals are particularly strongly stabilized when both an electron-attracting and an electron-donating substituent are present at the radical site. This has been called mero-stabilization" or " capto-dative stabilization. This type of stabilization results from mutual reinforcement of the two substituent effects. Scheme 12.3 gives some information on the stability of this type of radical. 

A key factor in doing a successful suspension polymerization is the composition of the aqueous phase or stabilizer. Too much stabilizer results in emulsion polymerization, which produces small particles (less than 1 /cm). Too little stabilizer results in bulk polymerization. For the production of GPC gels, the ratio of aqueous phase to organic phase should be about 2 1. 

Iborra and co-workers (Entry 8) examined the transesterification of N-acetyl-i-tyrosine ethyl ester in different ionic liquids and compared their stabilizing effect relative to that found with 1-propanol as solvent [36]. Despite the fact that the enzyme activity in the ionic liquids tested reached only 10 to 50 % of the value in 1-propanol, the increased stability resulted in higher final product concentrations. Fixed water contents were used in both studies. 

The stability of an emulsion mud is an important factor that has to be closely monitored while drilling. Poor stability results in coalescence of the dispersed phase, and the emulsion will separate into two distinct layers. Presence of oil in the emulsion mud filtrate is an indication of emulsion instability. 

The propagation of the cationic chain end can only occur if the nucleophilicity of the counterion is reduced sufficiently that recombination with the cation is prevented. The counterion Br, which recombines rapidly with the cationic chain end, can be stabilized by the interaction with the Lewis acid, e.g. SbBr5. An increase in stability, resulting from increasing complexation of the counterion, can be seen by means of... 

Delocalization of electrons is important in chemistry. Electron delocalization is a major factor of the stabilities and the reactivities of molecules. The delocalization occurs through the interaction of an occupied orbital with a vacant orbital (Scheme 13). The two electrons occupy the stabilized orbital. There are no electrons in the destabilized orbital. The stabilization results from the interactions between the occupied and unoccupied orbitals. 

Table 7 Criteria of Stability Results for Carboxymethylcellulose Standard and Formulation ...

Quantitative assessment of the electrophilic character of various types of phosphenium ions has been attempted using computational studies on hydride and halide exchange reactions, and the results attribute to 1,3,2-diazaphospholenium ions a lower electrophilicity (and thus higher stability) than other types of phosphenium ions [20, 66], The gain in stability due to aromatic -delocalization is predicted to be somewhat larger than inductive stabilization resulting from exhaustive A-alkylation of the parent diaminophosphenium ion, [P(NH2)2]+. 

The very small value of ks/kp = 0.00063 for partitioning of [4+] reflects the strong aromatic stabilization of naphthalene [5]. This will reduce the activation barrier for deprotonation, provided aromaticity is partly developed in the reaction transition state. Thus, this aromatic stabilization results in both a large 20 kcal mol"1 (K 1015) driving force for the dehydration of [4]-OH to give [5],44,99 and a very small barrier for deprotonation of [4+] (kp > 1.6 x 1010 s 1). 

Table 3 Stability results for the stearoylamino acid esters on pure water subphases at 25°C using Cadenhead s criterion for stability.

It s a miracle that we re here at all. Most proteins are not very stable even though there are a large number of very favorable interactions that can be seen in the three-dimensional structure. The reason is that the favorable interactions are almost completely balanced by unfavorable interactions that occur when the protein folds. A reasonably small net protein stability results from a small net difference between two large numbers. There are lots of favorable interactions but also lots of unfavorable interactions. 

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