What is the mechanism for dehydration of aldoximes by acetic anhydride?enter image description here

My attempt: enter image description here I doubt if it's correct.

  • $\begingroup$ What do you think the mechanism is? This is a homework question, you should show some effort so we know we aren't just doing your homework for you. You can edit your post to include your thoughts/attempt. $\endgroup$
    – NotEvans.
    Commented Sep 4, 2016 at 15:22
  • $\begingroup$ homework is not restricted to questions coming from actual assignments from professors/teachers. "This tag may be applied to questions which are not homework but are similar to a homework problem. " $\endgroup$
    – DHMO
    Commented Sep 4, 2016 at 15:26
  • $\begingroup$ And you should show your effort nevertheless. $\endgroup$
    – DHMO
    Commented Sep 4, 2016 at 15:27
  • $\begingroup$ Let us continue this discussion in chat. $\endgroup$
    – JM97
    Commented Sep 4, 2016 at 15:42
  • $\begingroup$ 1) You should never just write C and want it to mean $\ce{CH3}$. Do not do this ever. At the very least, write three bonds not connected to anything to symbolise left-out hydrogens. (You may want to define what ‘unconnected bonds’ mean, depending on where you are.) 2) One of the carbons in your second structure has five bonds. That will not happen unless you are discussing non-classical cations. 3) Other than that, you’re pretty close. $\endgroup$
    – Jan
    Commented Sep 4, 2016 at 21:25

1 Answer 1



My proposed mechanism is a nucleophilic addition/elimination mechanism without a tautomerism step.

It is all concerted.

The first step, addition, features the oxygen in the (E)-propionaldoxime acting as a nucleophile to attack one of the carbonyl carbons in the acetic anhydride, which pushes electrons the carbonyl oxygen, making it negatively charged.

Then, the negatively charged oxygen strikes back, initiating a chain of concerted cyclic electron rearrangement which cleaves quite a few bonds, resulting in three molecules, completing the elimination step.


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