Electronic coupling frontier molecular orbital interactions

Electronic Coupling Frontier Molecular Orbital Interactions and Electronic Structure Calculations... 

Figure 7.12 Energy diagrams for surface-molecule interactions in the case of (a) strong electronic coupling, (b) weak electronic coupling, and (c) no electronic coupling. ek stands for an electronic continuum of the metal or semiconductor band, whereas , represents the energy of frontier molecular orbital involved in this interaction...

Nature of the Activation Effect One of the principal questions that may be interpreted with the help of theoretical methods is the reasons for the activation of nitriles toward DCA upon their coordination to a metal center. Traditionally, the reactivity of dipoles and dipolarophiles in the DCA reactions is explained in terms of the frontier molecular orbital (FMO) theory and depends on the predominant type of the FMO interaction. The coupling of nitrones with nitriles is usually controlled by the interaction of the highest occupied molecular orbital (HOMO) of nitrone and the lowest unoccupied molecular orbital (LUMO) of nitrile centered on the C N bond (so-called normal electron demand reactions). For such processes, the coordination of N CR to a Lewis acid (e.g., to a metal) decreases the LUMOncr energy, providing a smaller HOMOjii -one - LUMOncr and, hence, facilitates the DCA reaction (Fig. 13.1a). 

It is generally agreed that the catalytic activity is related to the nature of the central metal in the MN4, because it is expected that in a crucial step, the frontier molecular orbitals of the reacting molecule interact with the frontier orbitals located on the metal center, that facilitating electron transfer from or to the target molecule [27]. The catalytic activity of the adsorbed MN4 should therefore be correlated with the electron density located on the metal center, and with the formal potential of the corresponding redox couples [25-27]. 

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