Carbon‐13 nuclear magnetic resonance spectra of fentanyl analogs

Natural abundance carbon‐13 chemical shifts are reported for the hydrochloride salts of fentanyl (1a) and fifteen analogs. The signals are assigned on the basis of chemical shift theory, SFORD multiplicities, signal intensities, comparisons with model compounds, and thiophene carbon‐proton coupling constants. In addition to its forensic value, the data suggest that the solution conformations of the analogs are similar to that of fentanyl hydrochloride.