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

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Pierre Fellmann

Institut de Biologie Physicochimique, UMR CNRS 7099, 75005 Paris, France

Christine Cordier

ITODYS, UMR CNRS 7086, Université Paris 7, 75005 Paris, France

Alain Gevertz

UFR de Chimie, Service d''Enseignement et d''Instrumentation, Université Paris 7, BP 78251, Paris, France

J. Chem. Educ., 2006, 83 (3), p 432

DOI: 10.1021/ed083p432

Publication Date (Web): March 1, 2006

Section:

History, Education, and Documentation

Abstract

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 (ν_A - ν_B)/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.