Calculated energies of stabilization

Figure 3.3. Plot of calculated energy of stabilization of organic SDA in SSZ-13 (CHA) vs. experimentally observed crystallization time.

The calculated energy of stabilization of such an adduct (DZ-type basis set) is about 5 kcal/mol. Structure IV corresponds to the transition state of bimolecular addition of HCl to ethylene localized by the gradient norm minimization method. 

Scheme 5.15 Effect of the nucleophilicity of stereodirecting groups on the stereoselectivity. Correlation with the calculated energies of stabilization.

Calculated energies of stabilized cations corresponding to the anchimeric assistance from the positions 3, 4, and 6 were compared with the energies of two possible conformations of the nonstabiUzed oxocarbenium cation (Scheme 5.21). Two most stable conformations of the nonstabiUzed cation, H4 and undergo a nucleophilic attack preferentially from P- and a-sides, respectively, giving products with the opposite stereochemistry [49-55]. Calculations showed that a-selective conformation of the oxocarbenium ion is by almost 3kcalmol more stable than P-selective one, that is, the a-selectivity is intrinsic to this... 

The above calculation applies to independent sodium and fluoride ions, and does not take into account the electrostatic attraction between the oppositely charged ions, nor the repulsive force which operates at small interionic distances. In the crystal of NaF the distance of nearest approach of the sodium and fluoride ions is 231 pm, and Coulomb s law may be used to calculate the energy of stabilization due to electrostatic attraction between individual ion pairs ... 

A variety of methods have been used to determine the energy of stabilization of a carbocation by a /J-silicon substituent. Li and Stone45 studied the association of the trimethylsilicenium ion with alkenes in a mass spectrometer and have calculated the yS-silyl stabilization energies for the carbocations produced as shown in Table 2. 

Equation 1 compares the stability of substituted silicenium ions versus the parent SiH3+ (1). Equation 2 compares the stabilities of the correspondingly substituted carbocations versus CH3+. Equation 3 compares the stabilities of silicenium ions with those of the corresponding carbocations. The calculated energies of equations 1-3 are presented in Table 1, and the following conclusions can be drawn51 ... 

Fig. 9. Calculated overall free energy of stabilization (AGtota ) for yeast phos-phoglycerate kinase at pH 6.5 and 0.7 M GuHCl. This curve displays two zeros, corresponding to the temperatures of cold and heat denaturation. Also shown in the curve are the cooperative Gibbs free energies (AG ) associated with the uncompensated exposure of apolar surfaces on unfolding of each of the domains. For both domains, AG is positive for the heat denaturation and close to zero for the cold denaturation. This behavior results in a cooperative heat denaturation and a non-cooperative cold denaturation. [Reprinted from Freire el al. (1991).]...

The stability of divalent group-14 diyl compounds E(PH2)2 with respect to isomerization to the systems with E=P double bonds (PH2)HE=PH (E = Si to Pb) has been reported in a combined experimental/theoretical work about diphosphanyl and diarsanyl substituted carbene homologues by Driess et al.147. Table 33 shows the calculated energies of the adducts, transition states and products of the rearrangement of the model compounds. It becomes obvious that the stability of the diyl form E(PH2)2 F relative to G increases with Si < Ge < Sn < Pb. 

In order to find a suitable candidate to direct for the HYP-14 MR material that is related to SSZ-48, a library of bulky decahydroquinolinium derivatized molecules was developed and the van der Waals energy of stabilization of the molecules within the pores of SSZ-48 and the related HYP-14 MR material was calculated using molecular modeling. In addition to stabilizing the HYP-14 MR structure over the SSZ-48 structure, the stabilization of the commonly encountered large-pore zeolite BEA by the molecules is calculated in order to locate an SDA molecule that also stabilizes the HYP-14 MR structure over BEA (in high-silica syntheses, often, MFI, MTW and BEA quickly form [48] with the organic outlined below, MFI and MTW could not be crystallized... 

What then, can organic chemistry as a science draw out from quantum chemistry In the search for the answer it is useful to look at the already accumulated experience of the interactions in these closely related areas of chemical science. In the last decades there have evolved various methods for the non-empirical and semi-empirical calculations of structure and reactivity of organic molecules based on quantum mechanics. In numerous cases these calculations turned out to be of extreme usefulness in obtaining quantitative information such as the charge distribution in a molecule, the reaction indices of alternate reaction centers, the energy of stabilization for various structures, the plausible shape of potential energy surfaces for chemical transformations, etc. This list seems to include almost all parameters that are needed for the explanation and prediction of the reactivity of a compound, that is, for solving the main chemical task. Yet there are several intrinsic defaults that impose rather severe limitations on the scope of the reliability of this approach. 

If we exclude the results for BE and assume for the other alcohols that the forward rate constant kj is diffusion controlled and approximately constant, the decrease in the exit rate of the surfactant represents a measure of the Gibbs energy of stabilization per CH2 group of the alcohol. From AGs = RT din (kj")/dnc, AGs = -450 J mol l per CH2. A similar calculation using data derived from the Hall model gives an estimate of AGs = -220 J mol-1 per CH2. 

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