[davidenarb]

Hi all,

I would like to understand why the equilibrium will favor the compound that has the larger pka (the basic compound) ?

please I am looking just for a short and logic explanation

[rwiew]

OK, let's try to get you to think about this. What is pKa defined is, what does it mean?

[davidenarb]

OK, let's try to get you to think about this. What is pKa defined is, what does it mean?

pka is a value to tell us the strength of an acid (the shorter the pka, the stronger the acid)

[rwiew]

Perfect, so now we have two acids - water and butane. You said the smaller the pKa, the stronger the acid - so you can see that water is a much stronger acid than butane, it wants to give the proton away much more than butane does hence the right side of the equilibrium is much favoured. I think some confusion might be coming from the fact that in your first post you said "compound that has the larger pka (the basic compound)" - a large pKa does not mean that the compound itself is basic, but that it's conjugate base (in this case the carbanion) is a strong one - hence it wants to get protonated. Is this making sense to you now?

[davidenarb]

Perfect, so now we have two acids - water and butane. You said the smaller the pKa, the stronger the acid - so you can see that water is a much stronger acid than butane, it wants to give the proton away much more than butane does hence the right side of the equilibrium is much favoured. I think some confusion might be coming from the fact that in your first post you said "compound that has the larger pka (the basic compound)" - a large pKa does not mean that the compound itself is basic, but that it's conjugate base (in this case the carbanion) is a strong one - hence it wants to get protonated. Is this making sense to you now?

Perfect !!! thanks