Correlation energy intramolecular

Table 3.3. Correlation between Intramolecular Strain from Molecular Mechanics (MM) Calculations and Activation Energies for Dissociation of C—C Bonds in Substituted Ethanes"...

Floating point, 276 Fluorine, ion, electronic correlation energy, 240 London energy, 78 molecules, intramolecular London energies, 78... 

Concerted bond-forming/bond-breaking processes at tetrahedral carbon (the familiar SN2 reaction) are not easily studied by the crystal structure correlation method. The preferred approach of a nucleophile is sterically more encumbered than the approach to a singly or doubly bonded centre, and the transition states involved are generally of high energy. Intramolecular displacements, such as those described on pages 117-118, are a possible way round this problem, but no systematic study is available. 

Conventionally, correlation is explained as dynamic fluctuations in the electronic density. By definition, it is the difference of the exact energy from the HF energy. Correlation energy can be separated into dynamical and static contributions. Notice that exchange repulsion occurs between electrons of equal spin. This implies some correlated motion between these electrons which is absent for electrons of opposite spin in HF. When this correlation is related to intramolecular interactions it is called dispersion, a more difficult quantity to calculate. 

Table 3. ro o distances (A) and i HB (kJ/mol, without ZPVE correction) dependence on the basis set and correlation energy for some compounds with strong and very strong intramolecular hydrogen bond. Values without bibliographic references are Author s unpublished data. Values in brackets were obtained forcing the open conformation to full planarity... 

CT complex formation from excited states is a widespread phenomenon and consequently has been very extensively studied. 0 A structure-energy correlation of intramolecular CT state formation in a series of (N,N-diethylanilino) amines indicates that high polar excited states are involved (pg values range between 13.4-... 

Mechanism (1) was excluded because the rate remains unaffected when the reaction is conducted under high CO pressure and the AS values are much lower than is typical for reactions that are initiated by CO loss (see the section on Substitution of CO by phosphines). Mechanism (2) was excluded based on the rather small solvent dependence. Mechanism (3) was rejected because neither radical initiators nor radical scavengers have any influence on the reaction, and there is no correlation between AH and the homolytic C-X bond energies. Intramolecular attack by X on one of the CO ligands (mechanism 4) is conceivable when X contains lone pairs (Cl, Br, SePh and TePh) but not with X = SnPh3 or PbPh3 and was also excluded. 

Equation (149) proves that Ecorr. of a saturated molecule is exactly equal to the sum of the bond, lone-pair and ion-core correlation energies and the intramolecular van der Wools attractions between these groups. This result is as accurate as the SchrSdinger equation itself but so far it is purely formal. The exact that appear in Eq. U48) are related to the exact %, Eq. (20), in the same way as the Vij of Eq. (60) were they can in principle depend on all the other terms of %. 

Correlation between intramolecular strain and activation energies for dissociation of C—C bonds in substituted ethanes... 

Since the zeroth-order equations are solved only in the Hartree-Fock approximation, the perturbation corrections account not only for intermolec-ular interactions, but for the intramolecular correlation energy as well. These two effects cannot be separated in the Lowdin basis set, but one may subtract the contributions of those [ij kl] integrals which result in local correlation. 

Hydrogen molecule, carbon oxide intramolecular energy, 110 clathrates, 12, 20 correlated wave function, 300... 

Intramolecular Isotope Effects. The data in Figure 2 clearly illustrate the failure of the experimental results in following the predicted velocity dependence of the Langevin cross-section. The remark has been frequently made that in the reactions of complex ions with molecules, hydrocarbon systems etc., experimental cross-sections correlate better with an E l than E 112 dependence on reactant ion kinetic energy (14, 24). This energy dependence of reaction presents a fundamental problem with respect to the nature of the ion-molecule interaction potential. So far no theory has been proposed which quantitatively predicts the E l dependence, and under these circumstances interpreting the experiment in these terms is questionable. 

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