Ground state stabilization

A solvated anion (reduced nucleophilicity due to enhanced ground-state stability)... 

The above mentioned deformation in the porphyrin diacid results in decreases in the free energy of activation for thermal atrop-isomerization, AG, of 2-3 kcal/mole compared to the corresponding free bases ( l) Even in the thermal isomerization the greater ground state stability of the trans-2,2 compared to the other isomers is apparent, although not nearly so much so as in the corresponding excited state. 

AG (R—>C2H4) 19 kcal mol (-25 °C). The relative ground state stabilities... 

The higher energy barrier in 153 than in 152 cannot be attributed (75T1813) to steric interactions, which destabilize the ground state of derivative 153, but rather to conjugation between the C=S and C=0 groups, which contributes to the ground-state stability of 153. 

Despite these advantages, native enzymes almost universally exhibit very low activities in organic solvents-often 4-5 orders of magnitude lower than in aqueous solutions. This loss in catalytic activity may be attributed to several factors, including a decrease in the polarity of the enzyme s microenvironment, the loss of critical water residues from the enzyme s surface, the decreased conformational mobility of the enzyme s structure, ground-state stabilization of hydrophobic substrates, and deactivation during the preparation of the biocatalyst for use in nonaqueous media,... 

Stereoelectronic effects can have a profound effect on the ground-state structure of molecules, and can often help to explain counter-intuitive conformational preferences or spectroscopic features. Their effect on the energy of transition states is, however, less straightforward to predict. As stated by the Curtin-Hammett principle [75] (Section 1.4), reactions will proceed via energetically unfavorable conformers if these are more reactive (as is often the case) than better stabilized conformers. In such instances ground-state stabilization of certain conformers or the weakening of bonds by hyperconjugation will not necessarily be predictive for the outcome of a reaction. 

Ground-state stabilization by hyperconjugation can modify the reactivity of organic compounds significantly, and must be taken into account when estimating the stability of certain types of compound. Di- or polysubstituted methanes can have high ground-state stability if the substituents are simultaneously a-acceptors and jt-donors, as is observed for many heteroatoms. If, on the other hand, the substitu-... 

Scheme3.13. Ground state stabilization of polyfluoro- and polyalkoxymethanes[51,52].

Because both diastereomers lead to the same radicals R R2CH- 24 on thermolysis this difference has to be due to differences in the ground state stability. This has been confirmed by EFF calculations and can be understood easily on conformational grounds16 56). The minimum energy conformations of all members of the alkane series are gauche. 

Jorgenson et al. [42] have proposed a relationship to define the nephelauxetic effect by taking into account ground state stabilization in the complex compared to the aquo ion. Accordingly we have... 

Since the first integral vanishes if use is made of the ZDO approximation, the intensity is seen to be essentially due to the dipole moment of the polar CT configuration, and the transition moment is proportional to the coefficient A. But in reality the situation is much more complicated, as can be seen from the fact that the intensity can be markedly different from zero even in cases where the ground-state stabilization is very weak and A is therefore approximately zero. The reason may be that the wave functions Equation (2.28) and Equation (2.29) neglect locally excited states (Dewar and Thompson, 1966). Furthermore, it might be important, at least in cases of weak interaction, to take into account the overlap between donor and acceptor orbitals in calculating the transition moment from Equation (2.31). 

N-carbonyl bond is 12 + 2 kcal for N,N-dimethylacetamide. The relative degree of ground-state stabilization of carboxylic acid derivatives depends upon the group bonded to carbonyl and would be expected to follow the order ... 

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