Orbital reactions

A more complete analysis of interacting molecules would examine all of the involved MOs in a similar wty. A correlation diagram would be constructed to determine which reactant orbital is transformed into wfiich product orbital. Reactions which permit smooth transformation of the reactant orbitals to product orbitals without intervention of high-energy transition states or intermediates can be identified in this way. If no such transformation is possible, a much higher activation energy is likely since the absence of a smooth transformation implies that bonds must be broken before they can be reformed. This treatment is more complete than the frontier orbital treatment because it focuses attention not only on the reactants but also on the products. We will describe this method of analysis in more detail in Chapter 11. The qualitative approach that has been described here is a useful and simple wty to apply MO theory to reactivity problems, and we will employ it in subsequent chapters to problems in reactivity that are best described in MO terms. I... 

In one step of a reaction mechanism electrons flow from a site rich in electrons to an electron-deficient site. When you draw a mechanism you must make sure that the electrons flow in one direction only and neither meet at a point nor diverge from a point. One way to do this is to decide whether the mechanism is pushed by, say, a lone pair or an anion or whether it is pulled by, say, a cation, an empty orbital, or by the breaking of a reactive weak Jt bond or o bond. This is not just a device either. Extremely reactive molecules, such as fluorine gas, F2, react with almost anything—in this case because of the very electrophilic F-F o bond (low energy F-F o orbital). Reactions of F2 are pulled by the breaking of the F-F bond. The nearest thing in organic chemistry is probably the reactions of carbon cations such as those formed ... 

One of the problems that the early applications of the MCSCF method faced was the construction of the wave function. It was necessary to keep it short in order to make the calculations feasible. Thus, one had to decide beforehand which where the most important CSFs to include in the Cl expansion. Even if this is quite simple in a molecule like H2 it quickly becomes ambiguous for larger systems. However, the development of more efficient techniques to solve large Cl problems made another approach possible. Instead of having to choose individual CSFs, one could choose only the orbitals that were involved and then make a full Cl expansion in this (small) orbital space. In 1976 Ruedenberg introduced the orbital reaction space in which a complete Cl expansion was used (in principle). All orbitals were optimized—the Fully Optimized Reaction Space— FORS [21]. 

We continue to emphasize chemical reactions early in the book, leaving the more abstract material on orbitals for later chapters. In a course in which many students encounter chemistry for the first time, it seems especially important that we present the chemical nature of matter before we discuss the theoretical intricacies of atoms and orbitals. Reactions are inherently... 

The mechaiiism of the oxidative addition of silanes has been studied in detail. Like the addition of the reaction of silanes occurs by donation of electron density in the H-Si CT-orbital into a metal orbital of u-symmetry and back-donation of electron density from a metal orbital of tr-symmetry into the H-Si a -orbital. Reactions of optically active silanes occur with retention of configuration in the product, the metal occupies the position that the hydrogen occupied in the starting silane (Equation 6.18). Moreover, the oxidative addition has been shown by femtosecond flash photolytic and infrared spectroscopic methods to occur with prior formation of a silane complex, perhaps in parallel with the formation of complexes from slipping of the Cp ring or those resulting from coordination of the triethylsilane through ethyl C-H bonds. 

In the case of the sec-butyl radical, the carbon bearing the unpaired electron is sp hybridized and the unpaired electron lies in the unhybridized 2p orbital. Reaction... 

As illustrated in (8.2), a strong Lewis acid with Ic LP (w a) acceptor orbital will attack ale LF ( b) donor orbital of a Lewis base to yield a 2c dative BD ([Pg.206]

---