Hey all, so I'm going through my notes, and I have written that N--HO has the strongest hydrogen bond. This meaning the bond between a nitrogen and the hydrogen attached to an oxygen.
Can anyone explain this, I'm trying to find where I got this info from, but I'm pretty sure it's correct.
Thanks
To find which one is the strongest, you want two things: 1) a weak covalent bond between the atom holding the hydrogen and the hydrogen and 2) a "more covalent bond" between the atom attracting the hydrogen and the hydrogen. I'll explain this.
It classifies as the strongest because the oxygen is more electronegative than a nitrogen. So, the O-H covalent bond is weaker than the N-H covalent bond, because more of the electron density is around the oxygen in the O-H bond than is around the nitrogen in the N-H bond. This means that the O will hang on to the H less tightly than the N will. In other words, it's a good H-bond donor.
So the O-H bond is the weaker covalent bond. Now you want the atom attracting the proton to have more covalent character (stronger bond).
1) O - - - - H---O
or
2) N - - - - H---O
The N in example 2 holds the H more tightly than the O in example one because it's less electronegative. Since the electronegativity difference between the N and the H is smaller than between the O and the H, the N to H hydrogen bond must be stronger. In other words, the N is a better H-bond acceptor, because it will hold on to the donated proton more tightly than the O will by sharing its electrons more.
Another way to look at this is you want the H-bond donor to be more acidic (holds the proton weakly) and the H-bond acceptor to be more basic (holds the proton more tightly). Generally speaking, the O-H bond is more acidic than the N-H. That would of course make N more basic than O.
Hope this was clear and helpful!
