I am looking for a literature reference on the energetic cost of C−N rotation in hydroxamate group such in LC5 in water. I have been googling for a while.


Reference 1 reports the isomerization barrier for N‐methylacetohydroxamic acid. From the abstract:

We have now determined the activation barrier to C–N rotation from major to minor conformation of a small secondary HA in $\ce{D2O}$ to be 67.3 kJ/mol. The HA rotational barrier scales with solvent polarity, as is observed in amides, although the HA barrier is less than that of a comparable tertiary amide in aqueous solution.

N‐methylacetohydroxamic acid (image from PubChem):

PubChem image


  1. Stefanie P. Sippl, Paul B. White, Charles G. Fry, Sarah E. Volk, Lingxiao Ye, Heather L. Schenck. Kinetic and thermodynamic characterization of C–N bond rotation by N‐methylacetohydroxamic acid in aqueous media. Mag Res Chem 54 (2016), 46-50. DOI: 10.1002/mrc.4318.
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