Why do amides require much harsher conditions for hydrolysis than esters? Amides require much harsher conditions to hydrolyse than its ester homologue. An explanation given is that the orbitals holding the lone pair on the nitrogen overlaps with the C=O π-bond to give conjugation, thus introducing a &quot;partial&quot; π-bond between nitrogen and the carbonyl carbon. Consequently, this makes the bond harder to break.
However, for the ester homologue, doesn't this conjugation also happen? An explanation given is poorer overlapping of the orbitals. However, how is that true?
In addition, such explanation is given to show that C=O is shorter in ester than it is in amide. However, I still don't get why this is the case.
Dimethyl acetamide (DMA) is less susceptible to hydrolysis than ethyl acetate (EA). This statement is true for aqueous acid or base. The infrared (IR) frequency for the carbonyl group of DMA is 1662 cm-1 while EA is 1742 cm-1. The lower the frequency, the lower the energy and the more, relatively speaking, single bond character in the carbonyl group. Thus, the carbonyl group of DMA has less double bond character than that of EA. Because nitrogen can sustain a positive charge better than oxygen, resonance is more pronounced in DMA than in EA. Because resonance is stronger in DMA, its carbonyl group is less susceptible to nucleophilic attack. The carbonyl bond length of EA would be expected to be shorter than that for DMA because the more double bond character, the shorter the bond. It is no different than the carbon-carbon bond length in the series ethane, ethylene and acetylene.