Orbital, antibonding

The triplet excited state of H2 is obtained by promoting an electron to a higher-energy molecular orbital. This higher-energy (antibonding) orbital is written and can be considered to arise from two Is orbitals as follows ... 

The antibonding orbital remains empty for the free radical and both of the ions. 

What is the energy separation E2 — E of the bonding and antibonding orbitals in ethylene, assuming that the overlap integral S is 0.27 ... 

The O atom uses one of its sp or sp hybrids to form the CO a bond and antibond. When sp hybrids are used in conceptualizing the bonding, the other sp hybrid forms a lone pair orbital directed away from the CO bond axis one of the atomic p orbitals is involved in the CO n and 71 orbitals, while the other forms an in-plane non-bonding orbital. Alternatively, when sp hybrids are used, the two sp hybrids that do not interact with the C-atom sp2 orbital form the two non-bonding orbitals. Hence, the final picture of bonding, non-bonding, and antibonding orbitals does not depend on which hybrids one uses as intermediates. 

For example, the three NH bonding and three NH antibonding orbitals in NH3, when symmetry adapted within the C3V point group, cluster into ai and e mos as shown in the Figure below. The N-atom localized non-bonding lone pair orbital and the N-atom Is core orbital also belong to ai symmetry. 

The bonding n molecular orbital pair (with m = +1 and -1) is of Tty symmetry whereas the corresponding antibonding orbital is of Tig symmetry. Examples of such molecular orbital symmetries are shown above. 

It is well known that bonding and antibonding orbitals are formed when a pair of atomie orbitals from neighboring atoms interaet. The energy splitting between the bonding... 

The bonding, nonbonding, and antibonding orbitals of CH2 can be illustrated in the following manner ... 

Unfortunately, these methods require more technical sophistication on the part of the user. This is because there is no completely automated way to choose which configurations are in the calculation (called the active space). The user must determine which molecular orbitals to use. In choosing which orbitals to include, the user should ensure that the bonding and corresponding antibonding orbitals are correlated. The orbitals that will yield the most correlation... 

A molecular orbital description of benzene has three tt orbitals that are bonding and three that are antibonding Each of the bonding orbitals is fully occupied (two electrons each) and the antibonding orbitals are vacant... 

Antibonding orbital (Section 2 4) An orbital m a molecule m which an electron is less stable than when localized on an isolated atom... 

The bonding between carbon monoxide and transition-metal atoms is particularly important because transition metals, whether deposited on soHd supports or present as discrete complexes, are required as catalysts for the reaction between carbon monoxide and most organic molecules. A metal—carbon ( -bond forms by overlapping of metal orbitals with orbitals on carbon. Multiple-bond character between the metal and carbon occurs through formation of a metal-to-CO TT-bond by overlap of metal-i -TT orbitals with empty antibonding orbitals of carbon monoxide (Fig. 1). 

Fig. 2. Overlapping of the metal, M, t5 -orbitals with the ( -bonding and 7T (antibonding) orbitals in a terrninally bonded M—CO interaction (T).

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