Antibonding character

Another question is whether the filled orbitals are of a bonding or antibonding character. This is displayed on a crystal orbital overlap population (COOP) plot as shown in Figure 34.3. Typically, the positive bonding region is plotted to the right of the zero line. 

Repeat your analysis for the LUMO of ethene, 1,3-butadiene, 1,3,5-hexatriene and -carotene, except now focus on each orbital s net antibonding character. (Assume that LUMO energy rises as net antibonding character increases.) What effect does conjugation have on LUMO shape and energy Are your predictions for the HOMO-LUMO energy gap consistent with the experimental data ... 

II.S2. The degeneracy of the top occupied orbitals of cyclobutane has been verified by photoelectron spectroscopy. These orbitals are still overall bonding because their local bonding character dominates their interbond antibonding character. ... 

Cooper et al. [30] were successful in rationalizing the striking variation in the S-S equihbrium bond lengths of FSSF (189.0 pm), ClSSCl (195.0 pm) and HSSH (205.5 pm) using the spin coupled (modern valence bond) theory. In the disulfur dihalides, but not for HSSH, incipient hypercoordinate character is observed at sulfur, with two partial t-like interactions in approximately perpendicular planes, and some antibonding character in the S-X (X=F or Cl) bonds. In other words, it is the form of t-like orbitals that is most rele-... 

Scheme 10 The hybrids and antibonding character of the geniinal O-O interaction and the SEs...

On the one hand, the antibonding character of the SOMO appears clearly on the N-0 bond the 2p orbitals are slightly bent and pushed away from the center of... 

The extension of LU MO 129> explains the direction of attack of H. The strong antibonding character of the C—O bond corresponds to the ring-opening reactivity. 

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. 

Clearly, the FCF angle tends to shrink despite F----F antibonding character as... 

Although these two derivatives are isoelectronic with [Fe3(CO)i2], both exhibit irreversible reduction processes. This observation is in agreement with the theoretical prediction that the LUMO of [M3(CO)i2] compounds, which are electronically saturated (48 valence electrons), is metal-metal antibonding, and the antibonding character follows the order Os > Ru > Fe. 

Then an increase in antibonding character could rednce the bond strength and the force constant of stretching vibration. It should be emphasized that despite the variety of interpretations, pressure effects are observed clearly and confirm independently the existence of dihydrogen bonds. 

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