The system ABXYM in nuclear magnetic resonance spectroscopy. Analysis of 3,4-dehydroprolinamide spectra by ABXYM and ABCDE methods

Abstract

The wide range of deceptive simplicities observed in spectra of 3,4- dehydro-prolinamide in different solvents makes analysis extremely difficult. The power of an approach using ABXYM tables combined with iterative computation is demonstrated to obtain accurate parameters for spectra of saturated solutions in deutero-chloroform and deuterium oxide. A detailed study of the effects of small changes in parameters on the observed spectral patterns provides a satisfactory explanation for each case of deceptive simplicity and, in particular, gives reasons for the added simplicity of spectra measured at 100 Mc/s. A trans- homoallylic coupling constant (J_2,5) of 5.8 c/s was observed and a synergistic four-bond coupling through the heteroatom is suggested to explain its magnitude. The stereochemistry of pyrrolines and similar heterocycles is discussed in the light of this large trans-coupling.