[cmk002]

Im looking at the resonance structures for both and I see that in both cases, the lone pair of electrons on the nitrogen is delocalized. In the case of methylhydrazine there is a negative charge formed on the other nitrogen, and in the case of acetamide the negative charge is on oxygen. I know that oxygen is more electronegative but im failing to see why that makes acetamide a stronger base.

Thank you !

[Dan]

Can you give a source/numbers?

According to this table, hydrazonium ion has a pKa of 8 (i.e. pKb of hydrazine is 4), whereas Wikipedia lists the pKa of protonated amides as aound -0.5 (i.e. pKb of amides as around 15.5). Hydrazines are much more basic than amides.

[cmk002]

I don't have a solid source, I was just reading my notes from a test review I just went to and apparently I wrote down that acetamide is more basic than methylhydrazine (it was one of those rank in terms of basicity practice questions).  Unfortunately I can't ask my professor because he is out of town for a week.  I was debating if I wrote my answers down wrong but I asked several other people and they said acetamide was more basic than methylhydrazine.  Whats frustrating is they said they don't know why/can't explain why but that it has something to do with the oxygen which makes no sense to me. 

If the oxygen is involved I imagine the basicity has something to do with an inductive effect.  The oxygen on the acetamide is a stronger electron withdrawing group, which would make the lone pair of electrons on the nitrogen less readily available to accept a hydrogen (this argument would agree with your post saying that amides are less basic than hydrazines, but contradicts what all my classmates are saying).

[spirochete]

Dan and the pKa table he gave are correct. Amides are not particularly basic, specifically because of the withdrawing carbonyl group. Amides are protonated at oxygen and their basicity is closer to that of water and alcohols than it is to amines.

If anything, the additional methyl group on methylhydrazine will make it more basic than hydrazine itself because alkyl groups are electron donating relative to hydrogen so they help to delocalize the positive charge in the protonated form.

As a general rule: electron donating groups=more basic and less acidic, and electron withdrawing groups = more acidic and less basic.

I'm not sure what you mean about negative charges on hydrazine; there are no resonance structures with formal negative charges on any form of hydrazine or methylhydrazine. And also there is no resonance delocalization in hydrazine, at least not in a way where you can draw a reasonable resonance structure as you would in sophomore organic.