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formation of the bonding MO (σ2p = 2pz,A + 2pz,B) and antibonding MO (σ2p* = 2pz,A − 2pz,B), respectively.

Schematic illustration of the formation of the fluorine molecule (F2) from two fluorine (F) atoms. Schematic illustration of the formation of (a) the C-C π bond from two equivalent p orbitals and (b) the C-O π bond from two nonequivalent p orbitals. equation equation

      The above equations show that for the formation of πp, the p orbital in oxygen (more electronegative) makes a greater contribution than does the p orbital in carbon (less electronegative). For the formation of πp*, the p orbital in carbon (less electronegative) makes a greater contribution than does the p orbital in oxygen (more electronegative). In each case, the bonding πp MO is responsible for the formation of a π bond, and antibonding orbital πp* is responsible for dissociation of the π bond.

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      The conjugate π‐bond of 1,3‐butadiene (CH2=CHCH=CH2), formed by sideway overlap of four p orbitals in the carbon atoms, consists of the following four MOs (Fig. 1.11b):

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      In each of the molecules, since all the p orbitals are from carbon atoms, their contributions to each of the MOs are equal.

      1.8.2 Molecular Orbital Diagrams

Schematic illustration of the formation of conjugate π bonds from p orbitals in (a) the allyl radical and (b) the 1,3-butadiene molecule. Chemical structures of the resonance stabilization of benzene.

      1.8.3 Resonance Stabilization

      By the nature, resonance stabilization is a result of electron delocalization in a molecule, which leads to decrease in energy and stabilizes the molecule. It typically occurs in the pπ systems. First, we will use the benzene molecule as an example to demonstrate the nature of resonance stabilization.

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