Kinetic and thermodynamic characterization of C–N bond rotation by N‐methylacetohydroxamic acid in aqueous media. (19th October 2015)

• Record Type: Journal Article
• Authors: Sippl, Stefanie P.; White, Paul B.; Fry, Charles G.; Volk, Sarah E.; Ye, Lingxiao; Schenck, Heather L.
• Is Part Of: Magnetic resonance in chemistry. Volume 54:Number 1(2016:Jan.)
• Page Start: 46
• Page End: 50
• Publication Date: 2015-10-19
• Subjects: NMR -- 1H -- hydroxamic acids -- EXSY -- rotational barrier -- Arrhenius analysis -- variable temperature; Nuclear magnetic resonance spectroscopy -- Periodicals; Chemistry, Organic -- Periodicals; Magnetic resonance -- Periodicals; 538.36
• DOI: 10.1002/mrc.4318
• Languages: English
• ISSNs: 0749-1581

Abstract

Abstract : Hydroxamic acids (HAs) perform tasks in medicine and industry that require bidentate metal binding. The two favored conformations of HAs are related by rotation around the C(=O)–N bond. The conformations are unequal in stability. Recently, we reported that the most stable conformation of a small secondary HA in water places the oxygen atoms anti to one another. The barrier to C–N bond rotation may therefore modulate metal binding by secondary HAs in aqueous media. We have now determined the activation barrier to C–N rotation from major to minor conformation of a small secondary HA in D2 O 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. Successful design of new secondary HAs to perform specific tasks requires solid understanding of rules governing HA structural behavior. Results from this work provide a more complete foundation for HA design efforts. Copyright © 2015 John Wiley & Sons, Ltd. Abstract : We report the activation barrier to C–N rotation from major to minor conformation of a small secondary hydroxamic acid in D2 O to be 67.3 kJ/mol. Comparison with literature indicates that the activation barrier scales with solvent polarity, as is seen in amides. Thermodynamic contributions to the measured rotational barrier are compared with reported values for a small tertiary amide.