<P> The mechanism which forms A and B is shown below . </P> <P> Aliphatic C-C or C-H bonds can lead to charge delocalization if these bonds are close to antiperiplanar to the leaving group . Corresponding intermediates are referred to a nonclassical ions, with the 2 - norbornyl system as the most well known case . </P>

Neighbouring group participation by sigma and pi bond