Which has lowest pka 2flourophenol Or 2chlorophenol Why? Ans: 2chlorophenol

1 Answer
anor277
Mar 25, 2018

We assess the acid base reaction...

#1,2-C_6H_4XOH(aq) +H_2O(l)rightleftharpoonsC_6H_4XO^(-) + H_3O^+#

Explanation:

Now as chemists, as physical scientists, we should first consult the data before we shoot off our mouths...

This site quotes #pK_a#, #"ortho-chlorophenol"=8.49#, and this site quotes #pK_a#, #"ortho-fluorophenol"=8.70#...and so chlorophenol is SLIGHTLY more acidic than fluorophenol. This is probably an ENTROPIC effect given that the chlorophenoxide is LARGER and LESS CHARGE DENSE than fluorophenoxide, and thus its protonolysis is more favourable.

In any event, would you relate the answer you are eventually given in this thread?

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