Delocalization interactions perturbation calculation

The balance of electrostatic and delocalization interactions in an isolated molecule may be perturbed by the influence of the solvent. In calculations based on Eq. 7, the analysis of solvation-energy terms suggested that the electrostatic contribution stabilizing the ap orientation of the acetal s ment is the conformationally dominant term. For example, in 2-methoxyoxane, the difference in energy of the (ap, ap) and (ap, sc) conformers in water, compared to that in the isolated molecule, caused by solute-solvent electrostatic interactions alone, amounts to 4 kJ.mor. Accordingly, the inter-and intra-molecular, electrostatic interactions operate in reverse directions in acetals. Whereas the intramolecular, electrostatic interactions are responsible, together with delocalization interactions, for the aiq)earance of the anomeric, reverse anomeric, and exo-anomeric effects, the solute-solvent electrostatic interactions lessen their im nitude, and may even cancel them. Of course, the solvent may also influence the electron distribution and energy of MO s in a molecule. In this way, the orbital interactions of lone-pairs and delocalization contributions to the anomeric effect may be scaled by the solvent, but this mechanism of the environmental effect is, in most cases, of only minor importance. 

To further address this question, DFT calculations were carried out on the actual complexes 115a and 115b. Here also, second-order perturbative NBO analyses provided evidence for dative Au-B interactions. The corresponding NBO delocalization energies ( 55 kcal/mol) are significantly higher than those found for the related MPB complexes 113 and 114, which further corroborated the strengthening of the Au-B interactions... 

The comparison of the ADAr parameters of the unfunctionalized, pyridyl-substituted triplet diradicals 12g ( — 0.01), 12i ( — 0.04), and 12k ( — 0.06) with the fury] derivatives 12c ( + 0.49) and 12m ( — 0.33) and the thienyl ones 12b ( + 0.61) and 121 ( — 0.12), makes it evident that the five-membered ring heteroaryl substituents interact much more strongly with the radical center. In view of the lower aromatic character of the five- versus the six-membered ring aryl substituents [63], the 6w-electron system of the former is more easily perturbed by spin delocalizing effects. Also the calculated spin densities (px) at the radical sites for the furyl and thienyl derivatives (Table 4) bear out this trend since the changes in px are more pronounced in the five- versus six-membered ring heteraryl substituents. 

Some of the contributions address the calculation of intermolecular forces at a fimdamental level, while the majority are concerned with appHcations, ranging from water clusters, through smfaces, to crystal structures. Sza-lewicz, Patkowski and Jeziorski provide a timely review of how perturbation theory can be used to address intermolecular forces in a systematic way. In particular, they describe a new version of symmetry-adapted perturbation theory, which is based on a density functional theory description of the monomers. The interpretation of bonding patterns for both intra- and intermolecular interactions is addressed in Popelier s review, which focuses on quantum chemical topology. He suggests a novel perspective for treating several of the most important contributions to intermolecular forces, and explains how these ideas are related to quantum delocalization. 

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