The question is : Why does triphenylmethane have such a high pKa value (going up to $33$)

My reasoning suggests that the conjugate base is highly stabilized and hence triphenylmethane should be a really good $\ce{H+}$ donor, but clearly isn't.

Where am I missing out?

  • 3
    $\begingroup$ "conjugate base is highly stabilized" - Why? Just because of resonance with a benzene ring? I suggest looking up the pKa of toluene to get an idea of how much stabilisation this actually provides. $\endgroup$
    – orthocresol
    Sep 16 at 15:33
  • 2
    $\begingroup$ Its the triphenylmethyl cation that is very stable, not the anion $\endgroup$
    – Waylander
    Sep 16 at 15:34
  • $\begingroup$ It's like 20 units less then methane - quite a lot of "stabilisation". $\endgroup$
    – Mithoron
    Sep 16 at 22:14
  • 3
    $\begingroup$ It is a very good H+ donor, as far as hydrocarbons go. $\endgroup$ Sep 16 at 23:24
  • $\begingroup$ Interestingly, diphenylmethane has about the same pKa as triphenylmethane. $\endgroup$
    – user55119
    Sep 17 at 0:22

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