91Ó°ÊÓ

The position of multiple bonds, charge and nonbonded electrons determine the site of delocalization of the electrons and charges.

The curved arrows illustrate the multiple bonds and charge movement among the atoms under resonance. The resulting structure is the second resonance structure.

Several resonance structures are combined to show one hybrid structure.

The delocalized multiple bonds are represented as dotted lines in a resonance hybrid structure. The delocalizing charges on two atoms (if any) are represented as partial negative or partial positive charges on the two concerning atoms.

a. In the given structure, the charge on both the oxygen atoms and multiple bonds in between oxygen-carbon-oxygen atoms are delocalized to give the second resonance structure.

Second resonance structure of a

The resonance hybrid structure is drawn by the combination of two resonance structures, giving a partial negative charge on both the oxygen-atoms and the delocalized pair of electrons distributed between the oxygen-carbon-oxygen atoms.

Resonance hybrid structure of a

b. The nonbonded electron pair is moved onto the ring, making a double bond between the oxygen-carbon,and the double bond in between carbon and oxygen is moved toward oxygen to give an extra electron pair to oxygen, resulting in a negative charge. This gives the second resonance structure.

Second resonance structure of b

The resonance hybrid structure is drawn from the combination of two resonance structures.

Resonance hybrid structure of b

c. Multiple bonds and site of charge are associated with two atoms only, that is, oxygen and carbon. The multiple bonds are moved toward the oxygen atom. Hence, removing the positive charge on oxygen-atom.

The positive charge is generated on the carbon atom, which is bonded with oxygen with a double bond in the given structure. The resulting structure is the second resonance structure.

Second resonance structure of c

The combination of the two resonating structures gives the resonance hybrid structure.

Resonance hybrid structure of c