Electrons in resonance structures

The curved-arrow formalism is universally used for keeping track of the flow of electrons in reactions. We have also used this device (in Section 1-9, for example) to keep track of electrons in resonance structures as we imagined their flow in going from one resonance structure to another. Remember that electrons do not flow in resonance structures they are simply delocalized. Still, the curved-arrow formalism helps our minds flow from one resonance structure to another. We will find ourselves constantly using these (red) curved arrows to keep track of electrons, both as reactants change to products and as we imagine additional resonance structures of a hybrid. 

Cbemists sometimes use curved arrows to specify the differences in positions of electrons in resonance structures. In SO3, for example, the repositioning of electrons in the resonance strac-tures can be indicated as follows ... 

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