Arrow formalism indicating resonance

Using correct arrow formalism, write the contributors to the resonance hybrid structure of the acetate ion, CH3C02. Indicate any formal charges. 

Scheme 6.93. The formation of the nitronium ion (NO2 ) from nitric (HONO2) and snlfuric (H2SO4) acids in the presence of methylbenzene (tolnene [C6HSCH3]) and the snbseqnent reaction of N02" to prodnce l-methyl-2-nitrobenzene (orf/jo-nitrotolnene), l-methyl-4-nitrobenzene (para-nitrotolnene), and l-methyl-3-nitrobenzene (mefa-nitrotolnene). Using the curved arrow to indicate the movement of a pair of electrons (as nsual) there is a resonance form in which the positive charge is formally placed on the ring carbon bearing the methyl (CH3-) group for the first two. No such form can be written for the last.

Draw the resonance contributing structure indicated by the curved arrows. Be certain to show all valence electrons and all formal charges. 

It is not necessary to waste time recalculating formal charges for each resonance structure, because the arrows indicate what is happening. Think of a positive charge as a hole of electron density—a place that is missing an electron. When we push it electrons to plug up the hole, a new hole is created nearby. In this way, the hole is simply moved from one location... 

Strategy Draw a valid Lewis structure for HPO , and determine whether and where electrons can be repositioned to produce one or more additional structures. Indicate the movement of electrons with curved arrows, and draw all possible resonance structures. Calculate the formal charge on each atom to determine the placement of charges. 

Write the resonance structure that would result from moving the electrons as the curved arrows indicate. Be sure to include formal charges if needed. 

Write the resonance structure that results when electrons are moved in the direction indicated by the curved arrows for the following amide. Calculate any formal charges that result. 

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