I'm curious to know what's the mechanism of: $$\ce{HF + D^+ \rightarrow DF + H^+}$$

  • 1
    $\begingroup$ Maybe you should include your own thoughts on this? $\endgroup$
    – tschoppi
    Commented Dec 8, 2013 at 14:02
  • $\begingroup$ @tschoppi. I have an idea (probably stupid) but I would prefer not to contaminate the discussion with it. $\endgroup$ Commented Dec 8, 2013 at 14:13
  • $\begingroup$ Well, you got my answer. I'd be curious to hear about your approach. $\endgroup$
    – tschoppi
    Commented Dec 8, 2013 at 14:53
  • $\begingroup$ The use of a double arrow is appropriate in this case. $\endgroup$ Commented Dec 9, 2013 at 3:37

2 Answers 2


To answer this question you should understand the kinetic isotope effect.

Since you deliver no real data about reaction rate constants I assume that the dissociation of $\ce{HF}$ is faster (has a larger $k_\text{dis}$) than the dissociation of $\ce{DF}$. I postulate the following mechanism:

$\ce{HF + D+ <=>[k_\text{dis}^\ce{HF}] H+ + F- + D+ <=>[][k_{\text{dis}}^\ce{DF}] DF + H+}$

Essentially it is a pretty simple reaction mechanism, but it tends to forming $\ce{DF}$ over $\ce{HF}$ because the deuterium dissociates more slowly.

  • $\begingroup$ I was thinking about an intermediate (HFD)+ based on some quantum mechanical calculations I performed. $\endgroup$ Commented Dec 8, 2013 at 14:58
  • $\begingroup$ Hm, given the high strength of the HF bond that is also entirely possible. Depending on the medium, of course. $\endgroup$
    – tschoppi
    Commented Dec 8, 2013 at 15:04
  • $\begingroup$ @ClaudeLeibovici That is probably a good description for a gas phase reaction. However, when inspecting the reaction in a condensed phase, calculations must be done much more carefully as bare hydrogen nuclei are extremely polarizing and will drag along one or more solvating entities with them. $\endgroup$ Commented Dec 8, 2013 at 19:28
  • $\begingroup$ Actually, $\ce{F-}$ isn't that stable, and one would expect a concerted mechanism. $\endgroup$
    – sencer
    Commented Dec 10, 2013 at 2:35

You know this happens in water all the time...what do you mean by mechanism? this is just proton jumping or hopping. The kinetics are are a side issue.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.