Nitration of anisole proceeds via the formation of nitronium ion by the action of nitrating mixture. The ortho attack of nitronium ion on anisole takes place by shifting of pi electron density of ortho position in benzene ring. The arenium ion so formed is resonance stabilized due to electron donating resonance effect of group. The required resonance structures are as shown below:
Analysis of all resonance structure clearly shows that the positive charge is delocalized in benzene ring. Thus, arenium ion is stabilizing itself by delocalizing the positive charge on every alternate carbon atoms. Moreover, the last resonance structure shows that octet of all the atoms are complete. Thus, structure is more stable among all resonance structures.
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