[LogicX]

I have 5 compounds here.  I have (1) propane with a carbanion on the end, (2)the same molecule as that but with an adjacent double bond to oxygen (its on the middle carbon), (3) C-C-O^-, (4) C-C-S^-, and (5) Br-.

I ranked them as (inc bascisity) 5<3<4<2<1.  I am pretty sure this is correct.

So, the pka of water, ethanethiol and ethanol are all generally around the same (14, 10.6, 16, respectively).  Wheras propane is around 50.  So I guess the answer would be the propane and acetone carbanions only?

[Arctic-Nation]

You've made a mistake: thiolates are actually less basic than alkoxides, so the correct order is 5 < 4 < 3 < 2 < 1.

Also, you're asking for the answer to a question you haven't asked.

[LogicX]

Sorry, I went to edit some stuff and it got erased somehow.  I'm trying to figure out which of those compounds is significantly more basic than water.

Why are thiolates less basic?  I see now that it has a lower pka, so it's conjugate base is weaker.  But sulfur is less electronegative than oxygen so it can't stabilize the negative charge as well, so it should be more basic.  So I guess the increasing size of sulfur which makes it more acidic is more important than electronegativity?

[Arctic-Nation]

Thiols are more acidic than alcohols because of the weaker bond strength with hydrogen: sulfur's large 3sp³ orbital is a poor match for hydrogen's small 1s orbital, so the proton is easily lost. This is directly comparable to the acidities of the halide acids: HCl is a weaker acid than HI, despite the fact that the latter's electronegativity is only a little bit above carbon's.

[opsomath]

Polarizability (ie size) nearly always trumps electronegativity when you're comparing bases. The criteria I teach my students is as follows:

1) Charge
2) Polarizability
3) Electronegativity
4) Resonance

in decreasing order of importance. So thiolates are more stable / less basic than alkoxides.

The list doesn't always work, but the exceptions (like strong acids) can be dealt with rationally as they crop up.