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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: AB01 on February 27, 2011, 03:50:38 PM

Title: which is more electronegative fluoride or trifluoromethyl anion
Post by: AB01 on February 27, 2011, 03:50:38 PM

Hi everyone,

I want to know which one is more electronegative F- or CF3- anion?

Thanks,

Abby

Title: Re: which is more electronegative fluoride or trifluoromethyl anion
Post by: Schrödinger on February 27, 2011, 11:15:27 PM

I don't understand why the concept of electronegativity need be applied to anions. Could you please explain the situation at hand? Whenever there is an anion involved, we usually don't speak of its electronegativity, since it already has a negative charge surrounding it (unless the situation demands discussing it, we don't take it seriously).

Title: Re: which is more electronegative fluoride or trifluoromethyl anion
Post by: AndersHoveland on March 01, 2011, 05:55:29 PM

I think you might mean "which group if more electronegetive F or CF3 ?",
in which case a flourine atom is somewhat more electronegetive. However, in certain
highly unusual examples, the CF3 group can allow more acidic or oxidizing compounds.

The trifluoromethyl anion rapidly decomposes into fluoride and difluorocarbene, the latter of which usually immediately dimerizes into C2F4.

Title: Re: which is more electronegative fluoride or trifluoromethyl anion
Post by: zolarpwr on March 14, 2011, 08:18:40 PM

Trifluoromethanesulfonic acid, CF3SO3H, has a pKa of -15.
Fluorosulfonic acid, FSO3H, has a pKa of -15.1.

Both are pretty much equivalent in acidity, meaning the anions that form are of nearly equal stability.

I agree that the term electronegativity isn't really appropriate for a polyatomic species since the other atoms can help stabilize the formal charge on one atom by inductive and resonance effects.