How come FCH2COOH is a stronger acid than BrCH2CH2COOH, but HBr is a stronger acid than H-F?
FCH2COOH vs. HF
- Thread starter SaintJude
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The more electronegative elements and the closer they are to the COOH, the more acidic the carboxylic acid is. F is more Eneg than Br, and so has a higher delta- than Br.
http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/crbacid1.htm
But for HBr and HF, well Br- is a larger ion and has a large electron cloud than F-, so it can stabilize the - charge better than F- when it deprotonates
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Ok, so by itself in an H-F molecule, F "can't help itself" and the strong H-F bond makes it a very weak acid.
But in conjunction with other EWGs, F helps stabilize the anionic conjugate base through induction (helps spread its electron density) and then thereby effectively stabilizes the strength of the corresponding acid.
, i think?
But in conjunction with other EWGs, F helps stabilize the anionic conjugate base through induction (helps spread its electron density) and then thereby effectively stabilizes the strength of the corresponding acid.
, i think?Ok, so by itself in an H-F molecule, F "can't help itself" and the strong H-F bond makes it a very weak acid.
But in conjunction with other EWGs, F helps stabilize the anionic conjugate base through induction (helps spread its electron density) and then thereby effectively stabilizes the strength of the corresponding acid.
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A non scientific exlanation is that oxygen wants lots of electrons, but halogens want them even more, so they steal from the oxygen. Fluorine wants electrons even more than bromine does, so the oxygens in the fluorine compound don't have enough electrons to be happy. They steal from the hydrogen and kick the hydrogen off knowing that they can get more electrons by being bound to something else.
