Confusion on electron withdrawing and donating effects of alkoxy, amide, ester groups

[deleted647690]

According to this picture from uworld, the OR portion of an ester is considered electron withdrawing, and the nitrogen portion of an amide is considered electron donating. I suppose I can see how, in the amide, the carbonyl oxygen is more electronegative than the amide nitrogen, thus it pulls electron density, making the Nitrogen donating.

However, why is an ester considered electron withdrawing? Both the Nitrogen and the oxygen of amides and esters, respectively, have lone pairs of electrons that they could share towards the carbonyl group. Wouldn't this make them both electron donating?
Carboxylic acid OH group is considered electron withdrawing. Ester OR group is considered electron withdrawing. Amide NRH group is considered electron donating. Is this because N is less electronegative than the carbonyl oxygen? All of these groups have lone pairs to donate and contribute to resonance stability, so I'd think they could all be electron donating. At the same time, they are all highly electronegative atoms, so could be seen as electron withdrawing as well.

Alternatively, why is an alkoxy group (-OR) considered electron donating? Again, the oxygen here has electron lone pairs to donate. At the same time, Oxygen is highly electronegative, so I'd expect it to have some withdrawing capacity.

I'm confused by this, as I see an oxygen atom and think that it would be electron withdrawing due to high electronegativity. This doesn't seem to be the case, as seen with alkoxy groups.
In addition, in the case of an ester, both oxygen atoms would be competing in terms of electronegativity difference.

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[deleted947265]

Amides and esters are donating or withdrawing groups in aromatic compounds based on whether they're bonded to aromatic ring by the carbonyl carbon or not. If they're bonded to the ring by the carbonyl carbon, they're electron withdrawing and deactivating because of the stability of the resonance structure. It makes a carbocation which is not stable. If the ring is bonded to the nitrogen/oxygen of the ester/amide the groups are activating/electron donating because it forms a resonance structure of a positively charged nitrogen/oxygen which is stable enough.

When considering the reactivity of the two groups consider the stability of their resonance structures. The ester resonance structure is positive charge on oxygen, which is less stable than a nitrogen with a positive charge.

 

[deleted647690]

Amides and esters are donating or withdrawing groups in aromatic compounds based on whether they're bonded to aromatic ring by the carbonyl carbon or not. If they're bonded to the ring by the carbonyl carbon, they're electron withdrawing and deactivating because of the stability of the resonance structure. It makes a carbocation which is not stable. If the ring is bonded to the nitrogen/oxygen of the ester/amide the groups are activating/electron donating because it forms a resonance structure of a positively charged nitrogen/oxygen which is stable enough.

When considering the reactivity of the two groups consider the stability of their resonance structures. The ester resonance structure is positive charge on oxygen, which is less stable than a nitrogen with a positive charge.

Okay, I see what you mean. Because the Nitrogen in the amide group is less electronegative, it is more stable with a positive charge (deficiency in electrons). It is more stable with a positive charge than the oxygen of an ester is with a positive charge. Therefore, the amide group is more likely to act in an electron donating fashion with the carbonyl, thus it is considered electron donating.

However, in the absence of that comparison, I still don't see why the ester group is considered electron withdrawing. Sure, it is "more" electron withdrawing than the amide group, because we are directly comparing them in this case. But in general, why is an ester considered electron withdrawing, when the oxygen of the ester group is just as electronegative as the carbonyl oxygen? Wouldn't both have equal strength in withdrawing electron density?

And I believe that normally, carbonyl oxygens are electron withdrawing, at least when comparing the oxygen to the carbonyl carbon. I would think that rule would hold true here, and therefore, the ester oxygen would be electron donating towards the electron withdrawing carbonyl group.

In fact, I've seen some sources say that ester OR groups are actually electron donating (at least in reference to aromatic substitution), which is contrary to what Uworld says.