Nonbonded molecular orbitals

Lone Pair. A pair of electrons contained in a Nonbonded Molecular Orbital. 

Nonbonded Molecular Orbital. A molecular orbital that does not show any significant bonding or antibonding characteristics. Nonbonded molecular orbitals often correspond to Lone Pairs. 

The double bond shown in different locations in the two resonance stmctures represents a pair of electrons in a delocalized n bonding molecular orbital that spans all three of the oxygen atoms, as shown in Figure I0-37a. One lone pair also appears in different positions in the two resonance stmctures, again signaling a delocalized orbital. This lone pair is spread over both outer atoms but not across the inner atom, as shown in Figure I0-37Z>. This is a nonbonding molecular orbital,. The lone pair shown in different positions in the resonance stmctures occupies the delocalized orbital. 

The nature and role of cycloheptatrienylidene (4a) has been a tantalizing puzzle to chemists since the 1960s. An appreciation for the reasons why begins with a consideration of the it,it, and carbenic nonbonding molecular orbitals of 4a, depicted in Fig. 8. 

For example, by combining the previous statements, Bingham formulates the following rule. Electron delocalization will, therefore, stabilize trans conformations relative to the corresponding cis structures when only bonding or nonbonding molecular orbitals are occupied. Cis conformations will be stabilized (less destabilized) relative to trans when antibonding molecular orbitals are also filled. ... 

The three LGOs of r1u symmetry that will overlap with the metal p orbitals are constructed in a similar manner, as shown in Fig. 11.19. Since the metal crbkals cannot participate in a-overlap, they are considered nonbonding molecular orbitals in complexes where there is no possibility for it bonding. In cases where there are ligand orbtals of appropriate symmetry available, the orbitals will be involved m n bonds. 

Figure 21-9 Energies and schematic representations of the it molecular orbitals of the 2-propenyl cation, 22. The calculated jr-electron energy of the cation is 2 a + 1.41/3) = 2a + 2.82/3. Orbitals with the energy a are neither bonding nor antibonding and are called nonbonding molecular orbitals (NBMO). The intermediate energy molecular orbital of the 2-propenyl cation is a NBMO because its component atomic orbitals, being on C1 and C3, are too far apart to be bonding or antibonding.

One reaches the same conclusion if the inversion is within the odd-membered chain. Then the symmetry of the nonbonding molecular orbital is reversed Cyclic interaction can occur for union with the 3-, 7-, 11-,... membered chains and not with the 5-, 9-, 13-,. . . membered chains. 

In any nonbonding molecular orbital (NBMO), the sum of the coefficients of the atoms s adjacent to a given atom r is zero. Hence the NBMO coefficients can be calculated very easily. The benzyl radical provides a nice example. All of the non-starred atoms have coefficients of zero. We give the para atom an arbitrary coefficient a. The sum of the coefficients of the atoms adjacent to the meta carbons must be zero, so the ortho coefficients are —a. For the sum of the coefficients around the ipso carbon to cancel, the benzylic carbon coefficient must be 2a. The value for a is given by the normalization condition ... 

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