Orbitals, antibonding

Figure 6.6 shows the molecular orbital energy diagrams for a few homonudear diatomic molecules. The stability of the molecules can be estimated from the number of electrons occupying bonding orbitals compared with the number of electrons in the antibonding orbitals. (Antibonding orbitals are sometimes denoted with the subscript, as in 2jt. )... 

All lone pair orbitals have a node between the two atoms and, hence, have a slightly antibonding character. This destabilizing effect of the lone pair localized molecular orbitals corresponds to the nonbonded repulsions between lone pair atomic orbitals in the valence bond theory. In the MO theory all bonding and antibonding resonance effects can be described as sums of contributions from orthogonal molecular orbitals. Hence, the nonbonded repulsions appear here as intra-orbital antibonding effects in contrast to the valence-bond description. 

The signs have been chosen to make the orbitals antibonding for positive values of the constants. This choice is based on the assumption of nodeless radial functions for all orbitals. If hydrogen-like radial functions are used, not all constants will be positive. 

Figure 4-8. Typical it and it orbitals, indicating the spatial distribution about the nuclei ( ) where the greatest probability of finding the electrons occurs (a) it orbital (bonding) and (b) it orbital (antibonding).

X = I, = -0.11 V) is such that the electron is probably removed from an orbital antibonding with respect to the metal-metal bond (70). 

The tetracobalt cubanes [ Co(/Li3-S)Cp 4] (67) (M = Co, E = S) have not been studied as extensively as the iron analogues (Section IV,B), but it is to be expected that electrochemical studies will reveal an extensive electron-transfer series. A comparison of the structures of [ Co(/i3-S)Cp 4] (2 = 0 and 1) showed that the nonbonded tetrahedron of metal atoms in the neutral molecule (Co—Coave = 329.5 pm) undergoes a tetragonal distortion. The shortening of four of the cobalt-cobalt distances (317.2 pm) is due to the removal of an electron from an orbital antibonding with respect to the four metal atoms 190). 

HeJ has three electrons, which are placed in MOs to give the ground-state configuration indicating that the ion has a doubly occupied cr is orbital (bonding) and a singly occupied orbital (antibonding). The bond order is... 

In addition to the occupied molecular orbitals which comprise the chemical bonds of molecules, each molecule has associated with it several higher-energy molecular orbitals which are normally unoccupied. These are called antibonding orbitals. Antibonding orbitals may have their electron density lying along the bonding axis and are then denoted as o -orbitals. 

Bonding molecular orbitals increase electron density between the nuclei and are lower in energy than individual atomic orbitals. Antibonding molecular orbitals have a region of zero electron density between the nuclei, and an energy level higher than that of the individual atomic orbitals. 

Define the following terms bonding molecular orbital, antibonding molecular orbital, pi molecular orbital, sigma molecular orbital. 

An electron in an antibonding orbital is of higher energy than if it were in a constituent atomic orbital. Antibonding orbitals are out-of-phase combinations of atomic orbitals. 

First, there are the N-> V transitions which are from the bonding orbital in the ground state of a molecule to a higher energy orbital (antibonding orbital)2. The class of N -> V transitions is large and one or more may occur for a molecule. For a transition between a orbitals as in the case of paraffins, the N V transition may be written as a 7r transitions. The <7 -> ultraviolet region. While some of the 7r r transitions are observed in the far... 

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