High‐resolution proton magnetic resonance spectra of morphine and its three O‐acetyl derivatives

High‐resolution 1H NMR (500 MHz) spectra were recorded for morphine, 3‐O‐acetylmorphine, 6‐O‐acetylmorphine and diacetylmorphine (heroin). Complete assignment of all proton resonances was made for these substances following determination of accurate chemical shift and coupling data by spectral simulation of all tightly coupled proton resonance patterns. Chemical shifts and proton couplings are discussed in terms of the conformation of rings C and D. From a varied collection of morphine analogs, torsion angles for ring D protons were obtained from crystallographic studies. The corresponding coupling constants were calculated, they demonstrate similar conformation of the ring D for the compared morphine compounds.