MO theory perturbational

As stated above, most radical anions encountered in the literature result from the addition of an electron to a formal n orbital. This is generally true because n orbitals are generally more accessible (energetically) than a orbitals, which are more localized and more strongly perturbed by the addition of an electron. However, from an electronic viewpoint there is no reason, a priori, to expect that all a bonds will be unstable to electron attachment. From simple perturbation MO theory, the interaction of a radical... 

A linear correlation between 13C chemical shifts and local n electron densities has been reported for monocyclic (4n + 2) n electron systems such as benzene and nonbenzenoid aromatic ions [76] (Section 3.1.3, Fig. 3.2). In contrast to theoretical predictions (86.7 ppm per n electron [75]), the experimental slope is 160 ppm per it electron (Fig. 3.2), so that additional parameters such as o electron density and bond order have to be taken into account [381]. Another semiempirical approach based on perturbational MO theory predicts alkyl-induced 13C chemical shifts in aromatic hydrocarbons by means of a two-parameter equation parameters are the atom-atom polarizability nijt obtained from HMO calculations, and an empirically determined substituent constant [382]. 

Professor Houk and I are coevals and we embarked on our research careers at about the same time. In the beginning of the 1970s, both he and I were independently working on mechanistic aspects of pericyclic reactions, using a combination of experiment, simple perturbational MO theory and semi-empirical MO calculations. My published work in this area was of variable quality whereas Ken s was uniformly... 

Here the term orbital may refer to a discrete molecular orbital or a band (or an atomic orbital in the case of atomic species). The donor orbital on the base is usually the highest occupied MO (or HOMO), and the acceptor orbital on the acid is usually the lowest unoccupied MO (or LUMO). Simple perturbational MO theory predicts that for two interacting orbitals of suitable symmetry and overlap, the smaller the difference in the orbital energies, the greater the mutual perturbation or interaction. The terms soft and hard relate to a range of properties, but essentially soft acids are... 

Photochemical addition of alkenes to C=N systems has been studied and interpreted by means of perturbation MO theory.(2- -2)-Cycloadducts (180) and (181) are formed on irradiation of the isoxazoline (182) in the presence of indene. ... 

Qualitative Application of MO Theory to Reactivity Perturbational MO Theory and Frontier Orbitals... 

The principal notions and conceptual systems of theoretical organic chemistry have been evolved from generalizations and rationalizations of the results of research into reaction mechanisms. In the sixties the data from quantum mechanical calculations began to be widely invoked to account for and predict the reactivity of organic compounds. In addition to and in place of the notions derived on the basis of the resonance and mesomerism theories that earlier had been treated semiquantitatively by means of correlation equations, novel research tools came to be employed such as reactivity indices, perturbation MO theory, or the Woodward-Hoffmann rules. It is very characteristic of these approaches, which have now taken firm root in the field of theoretical chemistry, that they, on the whole, imply an a priori assumption of the mechanism and probable structures of the transition states of reactions. 

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