How is H2O a nucleophile?

[jeffreyli1L]

Hello, how is H2O a nucleophile? I get that it has positive and negatively charged regions, but I don't see how this makes it a nucleophile.
Thank you!

[andrea_Disc3D]

Correct me if I'm wrong.
But I think it's because nucleophiles "donate" electrons and therefore tend to be species that have a negative charge or extra electrons. Oxygen in H2O has 2 lone pairs of electrons which are readily donated.

[Chem_Mod]

There are four factors that govern how good of a nucleophile a molecule is:
- Charge
- Electronegativity
- Solvent
- Steric hinderance

For the water molecule, we can see that it is polar, and has a transient negative charge on the oxygen.
In terms of electronegativity, it is less effective than that of Carbon or Nitrogen. The molecule of water only has two hydrogens attached, making steric hinderance almost a non factor. So we can see that it has two properties that would favor nucleophilicity, but its not the best nucleophile. Thus in the the absence of a better nucleophile, the water molecule can act as a nucleophile. Also, in the grand scheme of a reaction, it can be used to go from a greater relative energy state to a lower energy state, thus the interaction with water is going to be favorable.