H NMR spectra of substituted phenyl succinamic acids: A case study of deceptive simplicity

Abstract

NMR is an important technique used to establish purity of molecules; it is particularly important for molecules with pharmaceutical activity. The spectra for compounds containing para-substituted phenyl rings and 1,2-disubstituted ethylene groups often are deceptively simple that are analyzed in first-order terms when the spectra are second-order. The 1H NMR spectra for para-substituted phenyl succinamic acids are an example of molecules with deceptively simple spectra that have been analyzed in first-order terms when, in fact, the spectra contain two sets of second-order spectra. Using WINDNMR spectra simulation program, the 1H NMR spectra for a series of para-substituted phenyl succinamic acids have been analyzed. The two sets of second-order spectra are both AA′BB′ with very different values for the coupling constants. The differences in the second-order spectra for the ethylene group have been analyzed in ortho- and meta-substituted phenyl succinamic acids. Funding was provided in part by UNC-Charlotte and a grant from the NSF.