NOTE: Important charges and non-bonding electrons are shown throughout the animation except during the transition phase
Click the structures and reaction arrows in sequence to view the 3D models and animations respectively
In the reaction above the starting material is bicyclic and the product monocyclic, so a C-C bond must have been broken. This is known as a fragmentation reaction. C-C bonds are very strong and therefore difficult to break, but the reason this reaction works is because of polarization. It follows that to break a strong C-C bond, it helps if it is polarized.
For polarization to occur there needs to be a 'source' of electrons at one end, and an electron 'sink' (into which they can flow) at the other.