Tt bonding molecular orbitals

The combination of three p orbitals on one atom with three p orbitals on another leads to the formation of one a and two tt bonding molecular orbitals. The order in which the orbitals are populated is... 

Whal is wrong with the following sentence "The tt bonding molecular orbital in ethylene results from sideways overlap of twop atomic orbitals."... 

Figure 23.3 The tt bonding molecular orbitals of a conjugated enone (propenal) and a conjugated diene (1,3-butadiene) are similar in shape and are spread over the entire tt system.

Unlike the a bond formed as a result of end-on overlap, side-to-side overlap of two p atomic orbitals forms a pi (tt) bond (Figure 1.6). Side-to-side overlap of two in-phase p atomic orbitals forms a tt bonding molecular orbital, whereas side-to-side overlap of two out-of-phase p orbitals forms a rr antibonding molecular orbital. The TT bonding molecular orbital has one node—a nodal plane that passes through both nuclei. The TT antibonding molecular orbital has two nodal planes. Notice that a bonds are cylindrically symmetrical, but tt bonds are not. 

Side-to-side overlap of two parallel p orbitals to form a tt bonding molecular orbital and a tt antibonding molecular orbital. 

Cyclopentadienyl (Cp) complexes see Cyclopentadienyl) are known for almost all the metals of the periodic chart, including technetium. The compounds with transition metals usually possess covalent tt Cp-M bonding. The nature of the metal-Cp bond is multiple. The a-bond is formed from the overlap of an empty d orbital of Tc with one of the filled tt bonding molecular orbital on Cp with good symmetry. Back-donation is usually also present from the filled d orbitals of Tc to one of the empty n molecular orbitals on Cp. These molecules are usually called sandwich compounds see Sandwich Compound), when there are two Cp ligands bonded to the metal, or half-sandwich complexes see Half-sandwich Complexei) when only one Cp ligand is present. 

The two orbitals overlap side to side, so when the orbitals are in phase, a tt bonding molecular orbital would form. ... 

Fig. 20.3. Schematic representation of some non-bonding and tt-bonding molecular orbitals in SO2 or NO2. Left the non-bonding sp atomic orbital on the central atom and two delocalized lone pair orbitals formed by linear combinations of oxygen p orbitals in the molecular plane. Right the n molecular orbitals formed by linear combination of the valence shell pjc AOs of the three atoms. Comparison with the n orbitals of CO2 (Fig. 20.1) shows that the change from a linear to an angular structure has little effect on the n orbitals perpendicular to the molecular plane.

The combination of parallel 2p atomic orbitals by in-phase and out-of-phase addition of their wave functions to give a pi (tt) bonding molecular orbital and a pi antibonding molecular orbital tt ) is shown in Figure 1.21. A tt bonding molecular orbital has a nodal plane that cuts through both atomic nuclei, with electron density above and below the nodal plane concentrated between the nuclei. We picture all isolated tt bonds between carbons to have orbitals such as those of Figure 1.21. 

In the Lewis model, we use resonance forms to represent the two equivalent bonds, hi valence bond theory, it appears that the two oxygen-oxygen bonds should be different. hi molecular orbital theory, however, the ir molecular orbitals in ozone are formed from a linear combination of the three oxygen 2p orbitals and are delocalized over the entire molecule. The lowest energy tt bonding molecular orbital is shown here. 

The TT-bonding molecular orbital has all the 2p orbitals in phase. The 77-antibonding molecular orbital has all the three 2p orbitals out of phase. 

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