Bonding/antibonding orbitals

It ean be seen that the 3ag orbitals are bonding, the 3ay orbitals are antibonding, the ItIux... 

In summary, an atom or molecule has many orbitals (core, bonding, non-bonding, Rydberg, and antibonding) available to it occupancy of these orbitals in a particular manner gives rise to a configuration. If some orbitals are partially occupied in this configuration. 

Figure 15.3 The six benzene tt molecular orbitals. The bonding orbitals >p2 and t 3 have the same energy and are said to be degenerate, as are the antibonding orbitals tf/4 and 5. The orbitals and 4 have no tt electron density on two carbons because of a node passing through these atoms.

Donation from Lone-Pairs into Adjacent Antibonding Bond Orbitals, Anomeric Effect... 

Aromatic sextets can also be present in five- and seven-membered rings. If a five-membered ring has two double bonds and the fifth atom possesses an unshared pair of electrons, the ring has five p orbitals that can overlap to create five new orbitals— three bonding and two antibonding (Fig. 2.6). There are six electrons for these orbitals the four p orbitals of the double bonds each contribute one and the filled orbital contributes the other two. The six electrons occupy the bonding orbitals and constitute an aromatic sextet. The heterocyclic compounds pyrrole, thiophene, and... 

Butadiene has two n bonds. The interaction between the two n bonds is one of the simplest models to derive molecular orbitals from bond orbitals. A n bond in butadiene is similar to that in ethylene. The n bond is represented by the bonding and antibonding orbitals. The interactions occur between the n bonds in butadiene. The bond interactions are represented by the bond orbital interactions. 

Bonds interact with one another in molecules. The bond interactions are accompanied by the delocahzation of electrons from bond to bond and the polarization of bonds. In this section, bond orbitals (bonding and antibonding orbitals of bonds) including non-bonding orbitals for lone pairs are shown to interact in a cychc manner even in non-cychc conjugation. Conditions are derived for effective cychc orbital interactions or for a continuous orbital phase. 

Electron-donating orbitals are those occupied by electrons, i.e., bonding orbitals of bonds, non-bonding orbitals of lone pairs, HOMOs of molecnles, gronps and others. Electron-accepting orbitals are vacant orbitals, i.e., antibonding orbitals of bonds, vacant atomic orbitals on cationic centers, LUMOs of molecnles, gronps, etc. 

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. )... 

Figure 7.5 Bonding and antibonding molecular orbitals for the H2 molecule. Antibonding orbitais are higher energy orbitals than bonding orbitals.

Since upon excitation an electron is promoted from a bonding orbital to an antibonding orbital, the bond length is expected to increase. Hence, for ir-+ir transitions, in diagrams such as Figure 1.2, the excited state is drawn with a larger internuclear distance than the ground state. 

The NBOs are an optimized set of localized bonding, antibonding, and lone pair orbitals. The bond orbitals typically have occupancies of 1.98e in molecules with one simple Lewis structure. In C2H6, Weinhold and coworkers36 have shown that the barrier height V3 = 1025 cm-1 can be understood in the NBO terms in the form of aCH — donor-acceptor interactions. When the corresponding off-diagonal... 

Figure 1.24 How two isolated carbon p orbitals combine to form two n (pi) molecular orbitals. The bonding MO is of lower energy. The higher energy antibonding MO contains an additional node. (Both orbitals have a node in the plane containing the C and H atoms.)...

A bonding orbital always is lower than the antibonding orbital if they are derived from the same atomic orbitals. 

The first interaction, between CO 5c and Rh d,2, gives two new molecular orbitals. The bonding orbital has mostly 5<7 character, and it is customary to call it 5c. However, the level is lower than in free CO. UPS spectra reveal this shift immediately (see the spectrum of CO/Fe in Fig. 3.20) and indicate that its energy is close to that of the CO 1ft level. The antibonding chemisorption orbital has mainly d,2 character and is shifted upwards in energy. If the latter falls below the Fermi level, the 5c - d,2 interaction is entirely repulsive. For CO/Rh(100) the calculations indicate that the dz2 level falls across the Fermi level, such that the repulsion is partially relieved. 

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