Why picric acid is stronger than HBr in DMF but weaker than HBr in water?
Here's how it works.
Acidity is an equilibrium process. We measure acidity by determining the position of equilibrium of the ionization reaction
In a protic solvent like water, the
In the picrate ion, the negative charge is delocalized over the ring and the nitro groups, so the attractions to polar water molecules are much reduced.
Polar aprotic solvents like DMF preferentially solvate cations.
However, the large picrate anion, with its delocalized charge, is highly polarizable and is stabilized by ion-dipole interactions with the carbonyl group of DMF.
Thus, picric acid is a stronger acid than