stabilizing or destabilizing the nucleophile or transition state
Solvents (de)stabilize Nu and T.S.'s through
In water (polar protic solvent), nucleophilicity/rxn rate _________ down the P.T.
In acetone (polar aprotic solvents), nucleophilicity/rxn rate __________ down the P.T.
Why does nucleophilicity increase down the P.T. in polar protic solvents?
Bigger nucleophiles are easier to pull away from water, so they are better able to react and require a smaller activation energy. Smaller nucleophiles (especially F) are stabilized by hydrogen bonding and are harder to pull away from water, causing the reaction to have a higher activation energy.