Stability hyperconjugation

The position of the equilibrium A depends upon which provides the greater stabilization, hyperconjugation or onium ion bridging. 

To express the collective solvent reaction coordinate as in equation (6), it is necessary to define the specific diabatic potential surface for the reactant and product state. This, however, is not a simple task, and there is no unique way of defining such diabatic states. What is needed is a method that allows the preservation of the formal charges of the fragments of reactant and product resonance states. At the same time, solvent effects can be incorporated into electronic structure calculations in molecular dynamics and Monte Carlo simulations. Recently, we developed a block-localized wave function (BLW) method for studying resonance stabilization, hyperconjugation effects, and interaction energy decomposition of organic molecules.20-23 The BLW method can be formulated to specify the effective VB states.14... 

The SE° and GSE° values of a series of alkyl-substituted alkenes are collected in Table XXVI. It is seen that the (stabilizing) hyperconjugation energy is approximately equal to 3.2 kcal mol 1, whatever the alkyl group attached to the double bond may be. Moreover, the global stabilization of cis-2-butene is smaller than that of trans-2-butene due to the steric repulsion between the methyl groups in cis position. 

It is interesting to consider stabilizing hyperconjugative interactions in methanediselenol (130) (148). Two interactions need to be taken into account 3psc-ffc—se 3pse-ffc—H- The former, in the sc, sc, +sc, — sc, and ap,ap... 

Stabilizing hyperconjugative effects in the axial and equatorial "hyperconjomers" of cyclohexyl... 

Figure 8.11 Geometric progression that connects stabilizing to non-stabilizing hyperconjugative interactions. The bottom part of the list also shows how hybridization of the lone pair can change the efficiency of through-...

Figure 9.12 Comparison of the dominant transition state stabilizing hyperconjugative interactions for axial and equatorial nucleophilic addition to cyclohexanone according to the Cieplak s model compared to the...

An interpretation of the magnitude of p is difficult since many factors are involved. One sees, for example, the effect of inductive electron withdrawal on the p values of (31) and (32) by their comparison with the saturated isomers (33) and (38)." Hyperconjugation is also said to be a factor " Compounds stabilized hyperconjugatively [such as (36)] have low values of p, whereas compounds with little hyperconjugative stabilization [such as (23)] have high values of p. Yet it is difficult to rationalize from our present knowledge of inductive and hyperconjugative effects why the bi-cyclic and cyclic derivatives (33) and (35), which have nearly equal p values, should have a p value so unlike the structurally similar acyclic system (37)." ... 

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