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During acid catalyzed hydrolysis of ester why does the carbonyl oxygen attack the $\ce{H^{+}}$ ? Why doesn't the alkoxy oxygen which is more electron rich and less electronegative not attack the $\ce{H^{+}}$ with its lone pair? Any ideas?

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  • $\begingroup$ Why do you think that it is more electron rich? $\endgroup$ – Del Pate Apr 28 '15 at 13:32
  • $\begingroup$ Because one is sp2 hybrid while other is sp3 hybrid. $\endgroup$ – user14857 Apr 28 '15 at 14:06
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The difference between the carbonyl oxygen (red in colour) and alkoxy oxygen (blue in colour) is that the highly distorted pi-electron density (green shaded) towards to the carbonyl oxygen, due to more electro-negativity of oxygen that is the feature which is more on this oxygen than alkoxy oxygen . That feature provide the cavity for the H+ ion from acid, and the distortion of sigma- electron density at alkoxy oxygen is comparatively less than the distortion of pi-electron density at carbonyl oxygen.

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