Rank the following molecules from most to least acidic?

[gammagirl]

Fellow companions,  I am following the rules of charge, atoms, resonance, inductive effects, and orbitals. For (c) I do not understand why molecule 1 is ranked first.  I would have thought molecule 3 would be the most acidic because of atoms and the ortho arrangement. Please enlighten me as soon as possible. Why would the first molecule win? Anyways, that is what the answer key says.

[hypervalent_iodine]

That's a tough one. Without any other information, I would have put them at about the same pKa. Indeed, looking it up, their pKa's are remarkably similar. If I were to guess, I would say that the 2-chloro substituent of compound 1 helps stabilise the conjugate base through inductive effects moreso than the phenyl ring does in compound 3. That is really what it comes down to with acidity. The more stable the conjugate base, the more favoured the dissociation is, meaning more H+ in solution and higher acidity. 

[gammagirl]

You always come through. Thanks for confirming. I appreciate you.