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triplej
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Can anyone explain concisely why Trifluoroacetic Acid is more acidic than Trichloroacetic Acid, but HCl is more acidic than HF?
aroc91 said:Well, let's start with HF and HCl. We know that HCl is stronger because Cl is more electronegative, making the H+ ion more likely to leave.
In the case of halogenated acids, you have to look at the partial charges. The halogens, because they have a strong partial negative charge, put a partial positive charge on the carbon they're attached to. That, in turn, puts a partial negative charge charge on the carbon in the carboxylic acid functional group. That partial negative makes the oxygen in the OH group slightly positive.
Since Cl has a stronger partial negative than F, the oxygen on the trichloroacetic acid will have a stronger positive charge than the oxygen in the trifluoroacetic acid, making it a weaker base, because of the same reasoning used with HCl and HF.
Does that make sense? It's all about keeping track of the partial charges and knowing how electronegativity of the atom attached to the acidic H affects the strength of the acid.
Yanick said:-snip-
Yanick said:Flourine is the most electronegative atom on the periodic table. If it was all about electronegativity than HF would be the strongest haloacid and HI the weakest (which is not the case at all).
triplej said:why Trifluoroacetic Acid is more acidic than Trichloroacetic Acid
Electronegativity is a measure of an atom's ability to attract electrons towards itself in a chemical bond.
The electronegativity of halogens increases as you move from left to right on the periodic table. This is because the number of protons in the nucleus increases, leading to a stronger positive charge and a greater ability to attract electrons.
Fluorine has the highest electronegativity of all the halogens. Its small atomic size and high nuclear charge make it highly electronegative.
Halogens have a strong desire to gain an extra electron to achieve a stable octet configuration. This results in the formation of negative ions in chemical reactions.
The higher the electronegativity of a halogen, the more reactive it is. This is because a higher electronegativity means a stronger attraction for electrons, making it easier for the halogen to participate in chemical reactions.