Resonance energy Hess-Schaad

Topological Resonance Energies (TRE), Hess-Schaad Resonance Energies (HSRE), and Ring Current Indices (RCI) ... 

As rate constants of reactions of benzenoid hydrocarbons can be related to differences in energy of reactants and products (or intermediates) Hess-Schaad resonance energy differences can also be used as reactivity indices. Hess-Schaad resonance energies are defined as the difference between HMO ji energy and the additive contribution obtained by summing individual bond energies [42, 43]. Correlations of Hess-Schaad resonance energies with other HMO parameters have been discussed [44, 45],... 

Experimental log k2 values were correlated with Brown para-localization energies, Dewar reactivity numbers, Herndon structure count ratios, Hess-Schaad resonance energy differences, indices of free valence, and second-order perturbation stabilization energies. The latter are based on Fukui s frontier orbital theory [67] which classifies the Diels-Alder reaction of benzenoid hydrocarbons with maleic anhydride as mainly HOMO (aromatic hydrocarbon)-LUMO (maleic anhydride) controlled. However, the corresponding orbital interaction energy given by... 

Division of the Hess-Schaad resonance energy by the number of tt electrons gives the resonance energy per tt electron (REPE) of the compound. A compound with a substantially positive REPE value (greater than, say, 0.01 jS ) is predicted to be aromatic. A compound with a near-zero REPE is nonaromatic. A compound with a substantially negative REPE is predicted to be antiaromatic, being less stable than if its double bonds were isolated from one another. Some antiaromatic hydrocarbons are cyclobutadiene and fulvalene. 

The theory was described as being parameter-free in a sense that it avoids the use of empirical parameters for reference structure bond energies based on least-squares fitting of numerical data and that it does not need the distinction of eight bond references for hydrocarbon used in the Hess—Schaad scheme. The first papers were on hydrocarbons and gave similar results to the Hess—Schaad resonance energy (HSRE) method. The same, of course, is true for the papers by Aihara. ° It is clear, however, that such a theory cannot be parameter-free if heteroatoms are involved. These concern the /tx and /cc-x parameters of HMO theory. ... 

Hess and Schaad Hess-Schaad resonance energy E... 

After the advent of Dewar and Hess—Schaad resonance energies on the basis of the MO theory, a new VB approach to the resonance energy was advanced. The method is rather formalistic in using VB structures in a way similar to how the old Hiickel method used connectivity. For benzenoid hydrocarbons, a linear relationship between these VB resonance energies and the DRE values could be established. 

Vertical ionization potentials of 11.53 eV for a ionization and 11.75eV for n ionization and a dipole moment of 4.10 D were calculated [3]. Polarizabilities [5], the N chemical shift, the diamagnetic susceptibility, and Dewar and Hess-Schaad resonance energies were also calculated [6]. A very strong fundamental with Ai symmetry at 3922 cm" (SCF/DZP) or at 3700 cm"" (MBPT(2)/DZP) was predicted [4]. 

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