91Ó°ÊÓ

This type of polymerization occurs via carbanion intermediates. A monomer in this process must give a stabilized carbanion when it reacts with the anionic end of the growing chain. Monomers selected for this type of polymerization should have at least one electron withdrawing groups like carbonyl group, a cyano group or a nitro group.

A single structural formula sometimes cannot explain all the properties of a compound that is given. In such cases, the compound may be represented by two or more structural formulae which differ from each other only in the arrangement of electrons. None of this structural formula alone can explain all the observed properties of the compound. The compound is then said to show resonance. The various structures are known as resonating structures.

1. All resonance structures must have same number of valence electrons. The electrons are nor created nor destroyed in drawing resonance structures.
2. All resonance structures must obey the octet rule.
3. In space between the resonance structures, nuclei do not change their positions.