Larger atom better nucleophile?

[demolitionlvr]

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I don't understand how the larger the atom, the better the nucleophile in a protic solvent but for an aprotic solvent, its about basicity.

Also with basicity, there are two nucleophilic strengths in the KBB

one is :

RO> HO> RCO2> ROH > H2O

the second one is

F>Cl>Br>I

So are BOTH for only aprotic solvents?

 

[loveoforganic]

Protic solvents form solvent shells around anions. The tighter the charge distribution, the more tightly bound that solvent shell is and the weaker the ability of nucleophile to attack. Aprotic solvents don't form those solvent shells.

 

[Potatochips]

C N O F (The strength of nucleophile trend goes toward right) strong >>>>>> weak

Aprotic F > Cl > Br > I
Protic I > Br > Cl > F this is due to protic solvents being attracted around anions