Π Donation to Stabilize Positive Charge

Although oxygen is an electronegative element, it can share its lone pair electrons to stabilize positive charges on carbon.  This is seen in resonance stabilization in p-complexes formed in electrophilic aromatic substitution:

Compare the electrostatic potential maps (scaled identically) for reaction of benzene (top) and methoxybenzene (bottom) with a proton.  The neutral compound is on the left, the protonated intermediate on the right:


 

Notice how much less positive (blue) the methoxybenzene intermediate is!


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Last updated: 09/25/03
Comments to K. Gable