Comparison of the Resonance and Molecular-Orbital Methods

In this section, we will sketch the similarities and differences in the resonance (or valence-bond, VB) and molecular-orbital (MO) approaches for electron-pair bonds. 

Both methods normally start with atomic orbitals 1 s, 2s, 2p, and so on, of the types discussed in Section 6-1. Where the methods differ is in how these 

21 The Resonance and Molecular-Orbital Methods and Their Applications. Pericyclic Reactions (a) 

Remember, the MO method first combines the atomic orbitals to give molecular orbitals, then populates the molecular orbitals with electrons (no more than two paired electrons per orbital). This part of the procedure is similar to the way electrons are allocated to atomic orbitals (Section 6-1). 

The calculation then proceeds to predict a low-energy state and a high-energy state. These states can be regarded as hybrids of 1 and 2. The low-energy state, which is the one of more interest to us, usually is called a 

---