Orbital view of bonding

AN ORBITAL VIEW OF BONDING (A Supplementary, More Advanced Explanation)... 

An understanding of interaction diagrams is not absolutely necessary for using the principle of electron flow to predict organic reaction products. However, it is useful for understanding reactivity trends and the stability of reactive intermediates. This section relies on the principles discussed in Section 1.6, An Orbital View of Bonding. 

In the orbital view of bonding, atoms approach each other in such a way that their atomic orbitals can overlap to form a bond. For example, if two hydrogen atoms form a hydrogen molecule, their two spherical Is orbitals combine to form a new orbital that encompasses both of the atoms (see Figure 1.3). This orbital contains both valence electrons (one from each hydrogen). Like atomic orbitals, each molecular orbital can contain no more than two electrons. In the hydrogen molecule, these electrons mainly occupy the space between the two nuclei. 

Figure 16-26 The molecular orbital view of alkene—metal bonding according to Dewar.

Having just seen a resonance description of benzene, let s now look at the alternative molecular orbital description. An orbital view of benzene makes clear the cyclic conjugation of the benzene molecule and the equivalence of the. six carbon-carbon bonds. Benzene is a planar molecule with the shape of a regular hexagon. All C-C-C bond angles are 120 , all six carbon atoms are sp -hybridized, and each carbon has a p orbital perpendicular to the plane of the six-membered ring. 

Solids and Surfaces A Chemist s View of Bonding in Extended Structures by R. Hoffmann, VCH Publishers, New York New York, 1988. This book reflects the chemist s intuition as regards bonding in solids. Hoffmann has a special talent for constructing plausible models of the electronic structure of solids on the basis of insights strictly in terms of the crystalline geometry and the character of the underlying atomic orbitals. 

Fig. 23-2. Diagrams showing the molecular orbital view of olefin-metal bonding according to Dewar. The donor part of the bond is shown in (a), and the back-bonding...

Compare the Lewis structures with the molecular orbital view of the bonding in NO, NO+, and NOc Account for any discrepancies between the two models. 

The interaction with the 5 a orbital is called donative, because this doubly occupied orbital can only donate electrons to the sohd the interaction with the empty 2 k orbitals is backdonative. It can only accept electrons. This chemical bonding scheme is basic to the Chatt-Duncanson-Dewar chemical bonding view of bonding of CO with a metal atom in carbonyl complestes [26, 27] or the related Blyholder view when applied to surfaces [28]. 

Figure 10.1 gives an orbital overlap view of bonding in allyl cation. The planar structure of H2C=CHCH2" (Figure 10.1a) provides a framework that allows for continuous overlap of the 2p orbitals of the three adjacent 5/7 -hybridized carbons (Figure lO.lfo and c). Until now, we have only seen rr orbitals involving two adjacent carbons. Conjugated systems are characterized by extended rr orbitals that encompass three or more atoms. The electrostatic potential map (Figure 10.Id) shows the equal sharing of positive charge between the first and third carbons of 2C...

Molecular orbital diagram for the fictional ring structures of Li metal having n atoms. [Reproduced from Hoffmann, R. Solids and Surfaces A Chemists View of Bonding in Extended Structures, Wiley-VCH New York, 1989. This material is reproduced with permission of John Wiley Sons, Inc. ]... 

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