Amide-nitrogen is said that cannot be a hydrogen bond acceptor (Ref. 1). In my Gaussian opt simulation (B3LYP/6-31+G(d,p)) the result was consistent, which Amide-N didnt form intramolecular hydrogen bond with adjacent hydroxyl group (-OH).
What about iminol after amide tautomerization? In my simulation, Ive found strong intramolecular within iminol-N and adjacent -OH.
So i want to know that if thermal energy strong is enough to trigger tautomerization with hydrogen transfer? Or photoirradiation can trigger the process? (Ref. 2)
ref
1. J. Am. Chem. Soc., 1974, 96, 3794
2. J. Am. Chem. Soc., Vol. 109, No. 8, 1987
Thanks, now I get the resonance promoted tautomerization/hydrogen transfer. But what about typical amide bond?
I am not sure what means exactly the image, which is a mesomeric structure of a secondary amide. If you mean that proton transfer may occur between amide N-H and C=O, it is possible but probably highly endothermic/endergonic. The resulting C=N (H-bond acceptor) and O-H groups may be associated (suggested by Nizar Matar), but the geometry is far from optimal with this cyclic four-bond system. Though less stable than the amide form, the iminol may be (meta)stable in the gas phase, but specific solvation should certainly play a big role in the relative stability of the two tautomers. Substituents or adduct formation with acids may change the relatice stabilities.
You may consult for a more general survey:
Tautomeric Equilibria in Relation to Pi-Electron Delocalization, Ewa Daniela Raczyska et al; Chem. Rev., 2005, 105, 3561–3612.
The picture is over zoomed on the website, and clicking it can see the depict of amide-iminol resonance mechanism.
thanks, this is the exactly type of paper im interested in.
I'd like to further comment your last answer containing the ideas of "amide-iminol resonance mechanism". I'd comment that (i) resonance applies to a given single form, showing possible delocalization of electrons, and sites of high/low electron density; (ii) amide and iminol are two different species (tautomers) and have separate resonance forms. In fact, the scheme you show is wrong, even if it was published! The arrow connecting the two resonance forms (arrows on the left) should be a double-headed arrow, and the arrows on the right are correctly drawn as a double arrow connecting two tautomers (an equlibrium between two isomers). I tried to show a correct version in the attached figure (file "resonance+tautomers"). Anyway, I think it's misleading to mix resonance and tautomerism (or other isomerisms) in the same scheme, as on the first line of this figure. I advise to separate the two fundamentally different concepts in two shemes, like shemes (1) and (2) in my revised version.
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