Resumen de Study of an AB System within the 1H NMR Spectrum of a Maleamic Acid: Application of Chemical Exchange between Acid—Base Conjugates

Pierre Fellmann, Christine Cordier, Alain Gevertz

• The 1H NMR spectrum of the system of two coupled protons shows two dissymmetric doublets; the frequency and intensity of the four lines are defined by calculations in the field of quantum chemistry. We propose an experimental verification of these results employing two vicinal olefinic protons. A mixture of N-(2-nitrophenyl) maleamic acid and its conjugated base in d6-DMSO, owing to fast chemical exchange, gives the spectrum of a mean entity characterized by a ratio (νA - νB)/J, which is function of molar fraction of the base form. Values of this ratio between 0 and 7.1 (at 200 MHz) are examined.