Resonance Stabilization when electrons can't donate?

[FROGGBUSTER]

A question in ExamKrackers asks us why triphenylmethanol is so acidic. Link to the structure below:

http://en.wikipedia.org/wiki/Triphenylmethanol

Explanation:

Triphenylcarbinol is more acidic than ethanol because it has extensive resonance stabilization of the conjugate base's negative charge.

I'm not seeing how the lone pairs on the Oxygen could donate into any of the rings though. It can't donate those electrons onto the carbon it's next to or else that carbon would have 5 bonds.

Can someone explain? Thanks!

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[Arctangent]

I don't really get that explanation either. Even on the wikipedia page you posted, it said:

Typical of alcohols, resonance offers no stabilization of the conjugate base due to its being bonded to a saturated carbon atom.

which seems to directly contradict the given explanation.

 

[FROGGBUSTER]

I don't really get that explanation either. Even on the wikipedia page you posted, it said:
which seems to directly contradict the given explanation.

Interesting, I didn't read the Wiki page.

Can others chime in? I'm inclined to think ExamKrackers is wrong here. The weird thing is I've seen this reasoning in other types of problems in the EK book as well.

 

[BeatMCAT]

yeah i am pretty sure EK made the mistake. There is no way resonance of the negative charge on oxygen is possible in its conjugate base form. if anything i believe this is def not a strong acid. Reason being, the HUGE phenyl groups are electron donating (just like any R group is), therefore there is more negative charge on the molecule. The hydrogen, therefore, i believe would not be deprotonated as easily as it should for a strong acid because of the inductive effect. A molecule would be a strong acid if electron density was withdrawn from it.
Also, this problem might jsut be a glitch. If there was a pi bond present next to the conjugate base, then resonance would've occured, and then the ocnjugate base would be more stable (therefore weaker base), and by this logic, the acid is stronger. Resonance would beat inductive in this case.

 

[stsa84]

Unless EK has stumbled upon a loose thread that, if pulled, will unravel the very fabric of our reality, triphenylmethanol is not acidic.

Stabilization of the anion is impossible. The molecule may be more acidic than ethanol (as EK claims), but certainly not because "it has extensive resonance stabilization of the conjugate base's negative charge."

 

[whiteshadodw]

Unless EK has stumbled upon a loose thread that, if pulled, will unravel the very fabric of our reality, triphenylmethanol is not acidic.

Stabilization of the anion is impossible. The molecule may be more acidic than ethanol (as EK claims), but certainly not because "it has extensive resonance stabilization of the conjugate base's negative charge."

it might not be because of 'resonance' but benzene groups are certainly electron withdrawing, and so it could partially be because of inductance.

 

[MSU2009]

http://www.chemicalbook.com/ProductMSDSDetailCB3335936_EN.htm
According to the site above, the pKA of triphenylmethanol is 12.73.

If that is true, then the explanation that triphenylmethanol is more acidic than ethanol is true (pKA of EtOH is around 16). Though, the wiki article says it's expected to have a pKA of 16-19..