Orbital interaction concepts

MO calculations were performed rarely for thiopyrans except for an MNDO study of 2 [84ZN(A)267], Charge distribution and orbital interaction concepts were explored in an interpretation of model reactions of thiopyrylium ions with azides giving 68 and the corresponding 3,5-unsub-stituted thiopyrans (84T3549) as well as for the equilibria between 1 and 2 or 167 and 168, respectively (92JOC4431). 

The concept of electroauxiiiaiy is quite powerful to solve these problems. The pre-introduction of a silyl group as an electroauxiliary decreases the oxidation potential of dialkyl ethers by virtue of the orbital interaction. As a matter of fact, we demonstrated that the anodic oxidation of a-silyl ether took place smoothly in methanol.30 Selective dissociation of the C-Si bond occured and the methoxy group was introduced on the carbon to which the silyl group was attached. Therefore, a-silyl ethers seemed to serve as suitable precursors for alkoxycarbenium ions in the cation pool method. 

It is our hope that the reader will be stimulated to delve deeper into the world of orbital interactions and, hopefully, Fmd a chance to apply the key concepts to problems of direct interest. 

The Concept of Matrix Element and Energy Gap Controlled Orbital Interactions... 

The above considerations set up the stage for the introduction of the concept of energy gap controlled and matrix element controlled orbital interactions. 

Chapters 6-11 describe applications of orbital interaction theory to various chemical systems in order to show how familiar concepts such as acid and base strengths, nucleo-... 

This description, which uses a mixture of MO and valence bond concepts and attributes specific energies to hybrid orbitals, may appall the theoretician. It has the advantage, however, of reducing the problem to a series of two-orbital interactions, thus allowing us to find the CO orbitals very quickly. 

On the basis of the results of CNDO/2 calculations and the concept of orbital interaction, the intermediate B is expected to be in an excited state but the intermediate C and the intermediates from benzenoid disilanes are thought to be in the ground state. This may account for the anomalous chemical behavior of intermediate B (95). 

In the present contribution, we will examine the fundamentals of such an approach. We first describe some basic notions of the tight-binding method to build the COs of an infinite periodic solid. Then we consider how to analyze the nature of these COs from the viewpoint of orbital interaction by using some one-dimensional (ID) examples. We then introduce the notion of density of states (DOS) and its chemical analysis, which is especially valuable in understanding the structure of complex 3D sohds or in studying surface related phenomena. Later, we introduce the concept of Fermi surface needed to examine the transport properties of metallic systems and consider the different electronic instabilities of metals. Finally, a brief consideration of the more frequently used computational approaches to the electronic structure of solids is presented. 

Activation by Dynamic Coordination. As a method for the activation of tetraor-ganometals toward electron transfer, dynamic coordination has recently received significant research interest because it does not utilize orbital interactions. The utility of this concept is demonstrated by the following example The oxidation potential of (3-oxobu-tyl)tributylstannane is less positive than that of tetrabutylstannane (Table 7) [142]. 

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