Our research on the preparation and characterization of compounds that are specific Michael acceptors for thiol and thiolate portions of cysteine residues in proteins has unveiled some remarkable NMR data in one particular synthetic precursor.  N-ethylmaleamic acid (NEMA) gives rise to a rather ordinary 1H NMR spectrum.  Upon close examination, the vinyl protons give rise to a pair of well-resolved doublets that have tremendous chemical shift variability at low concentrations in CDCl3.  The chemical shifts of these two protons at a variety of decreasing concentrations eventually give rise to a coalescence of chemical shift(s) (??=0) followed by a �cross-over� of the doublet signals.  The high degree of inter- and intramolecular hydrogen bonding found in a single crystal X-ray structure of NEMA will be used as a structural reference point.  Additionally, observations of the 1H NMR spectra of NEMA in more polar solvents as well as 13C NMR data will be discussed.

Finding NEMA's vinyl protons: Unusual chemical shift variability in <sup>1</sup>H NMR spectra at low concentrations

244th National Meeting (2012)

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Finding NEMA's vinyl protons: Unusual chemical shift variability in 1H NMR spectra at low concentrations

Finding NEMA's vinyl protons: Unusual chemical shift variability in ¹H NMR spectra at low concentrations