Why is iodine more nucleophilic than fluorine?
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It depends on the nature of solution . deciding this is not the std criteria , depends on protic or aprotic solvent
I⁻ is a better nucleophile than F⁻ in polar protic solvents.
F⁻ is a better nucleophile than Br⁻ in polar aprotic solvents.
BTW ACCORDING TO UR QUESTIONS , THE REASON IS:-
A protic solvent has an H atom bound to O or N. It can use its H atom to participate in H-bonding with a nucleophile.
This creates a "shell" of solvent molecules around the nucleophile.
The nucleophile has to push this shell of solvent molecules out of the way to attack the carbon bearing the leaving group.
F⁻ is a small ion with a high charge density. It is tightly solvated.
I⁻ is a large ion with a low charge density. It is loosely solvated. There are only a few solvent molecules to push out of the way.
In polar protic solvents, the order of nucleophilicity is
I⁻ > Br⁻ > Cl⁻ > F⁻
I⁻ is a better nucleophile than F⁻ in polar protic solvents.
F⁻ is a better nucleophile than Br⁻ in polar aprotic solvents.
BTW ACCORDING TO UR QUESTIONS , THE REASON IS:-
A protic solvent has an H atom bound to O or N. It can use its H atom to participate in H-bonding with a nucleophile.
This creates a "shell" of solvent molecules around the nucleophile.
The nucleophile has to push this shell of solvent molecules out of the way to attack the carbon bearing the leaving group.
F⁻ is a small ion with a high charge density. It is tightly solvated.
I⁻ is a large ion with a low charge density. It is loosely solvated. There are only a few solvent molecules to push out of the way.
In polar protic solvents, the order of nucleophilicity is
I⁻ > Br⁻ > Cl⁻ > F⁻
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