but how is fluorine a better base than iodine but a worse nucleophile?

[tammie123]

but how is fluorine a better base than iodine but a worse nucleophile?

I understand that fluorine is a better base due to greater charge density (but what about the greater polarizability of iodine)
And I understand that iodine is a better nucleophile as as it more polarizable as it gives up the outer shell electrons more easily (but what about the increased charge density of fluorine).

This is what's confusing me the most

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[Jibby321]

I think it has to do with the electro negativity of Florine since it is greater. Something like that.

 

[rxlea]

Think about how far away from the nucleus the electrons are. Fluorine is kinda greedy and holds onto stuff tighter.

 

[Giannag]

Nucleophilicity increases going down a group on the periodic table but basicity increases going up a group . Strong acids have weak conjugate bases and weak acids make strong conjugate bases .

 

[5HT3]

HI dissociates completely, so any free I- will not accept any protons (what a base is supposed to do). HF is a weak acid, so some free F- will accept protons.

 

[chemguy79]

but how is fluorine a better base than iodine but a worse nucleophile?

I understand that fluorine is a better base due to greater charge density (but what about the greater polarizability of iodine)
And I understand that iodine is a better nucleophile as as it more polarizable as it gives up the outer shell electrons more easily (but what about the increased charge density of fluorine).

This is what's confusing me the most

Nucleophilicity changes if you're in a protic solvent versus an aprotic solvent. Remember that the trends are completely opposite. Iodine is a great nucleophile in a protic solvent, but a weaker nucleophile than fluorine in an aprotic solvent.

 

[owlegrad]

These sorts of questions are best asked in the PCAT forum. Thanks.