Increased-Valence Structures Some General Comments

2-6 Increased-Valence Structures Some General Comments 

Inspection of the increased-valence structures (I)-(VIII) shows that each of them involves electron distributions of the following types  

We may generalize these structures to write them as Y — A B. All increased-valence structures have this type of eleetron distribution for each set of eleetrons that is involved in 4-electron 3-centre bonding. As we shall demonstrate further in Chapter 11, we may generate this increased-valenee eleetron distribution by bonding a Pauling 3-electron bond stracture A B to a third atom Y which 

We are therefore led to conclude that all increased-valence structures for 4-electron 3-centre bonding units can have Pauling 3-electron bonds as components of their valence-bond structures. And because the phenomenon of 4-electron 3-centre bonding occurs extremely frequently, it follows that the relevance of Pauling 3-electron bond and increased-valence theory for qualitative valence-bond descriptions of electronic structure is very great. The need for an increased-valence theory has also been implied by Bent in his review on inter- and intramolecular donor and acceptor complexes. 

The discussion above shows that the general increased-valence structure Y — A-B for 4-electron 3-centre bonding has the following properties. These will be elaborated further in Chapters 11,12 and 14. 

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