what does canonical structure mean?

Canonical structures: When a single molecule is represented in more than one form with comparable energies due to the resonance ,then these different forms are called as resonating structures or canonical forms.

  • All these structures are inter convertible i.e.,they may shift from one form to another form but none of them can explain the full nature and structure of molecule, however , each of them explains some properties of the molecule.
  • These structures are represented with a double headed arrow as ;↔  but the complete structure is a hybrid of all these structures called as a resonance hybrid.
  • These structures arise because, in some molecule, the simple Lewis structure is not sufficient to explain all the properties, and so the bonded electrons are shifted in different manners to produce the corresponding canonical structures

Ex: in case of Ozone molecule (O3);

It occurs in two canonical structures which make a hybrid as:

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when a single structure cant define a molecule different structures r made by shifting of electrons....which r also called resonating structures or canonical structures..

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 In chemistry, resonance or mesomerism is a way of describing delocalised electrons within certain molecules or polytomic ions where the bonding cannot be expressed by one single lewis formula. A molecule or ion with such delocalized electrons is represented by several contributing structures  (also called resonance structures or canonical stuctures)

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