Homoallylic and Homobenzylic Cations

This section deals with the participation of the electrons of the adjacent n-bond (the olefin double bond or the aromatic ring) at the stage of the cation centre development, as well as with the formation of intermediate nonclassical homoallylic and homobenzylic ions. 

Just as in the case ofa-participation, the electrons of the neighbouring 7t-bond interact covalently with a carbon from which a halogen, a tosylate or other leaving group detaches, contributing thereby to the bond fission. This interaction (intramolecular nucleophilic substitution) occurs at the backside of the leaving group. 

The term homoallylic ion was introduced by Winstein when he studied the so-called cholesteryl-i-cholesteryl ion 770 This term stands for carbo- 

Later on Winstein extended the concept of homoconjugation for a nonclassical MO joining the atoms taking part in its formation into a cycUc system. A particular systems is that of homoaromatic compounds 233,341-344) aromaticity and 

1) increased stability of the substrate in comparison with the similar acyclic conjugate n-system  

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