A potentially useful simple method is proposed to determine whether theN-phenyl rings in the analgesic drug, antipyrine (and analogs), preferentially exist in a conformation which is approximately coplanar with, or is perpendicular to, the five-membered heterocyclic rings. The method is based on the magnitude of “spectral dispersion,” that is, the degree of NMR chemical shift differences for the proton and the protonated carbon signals of theN-phenyl. A narrow range of chemical shifts is considered suggestive of a preferred perpendicular conformation, which reduces mesomeric effects of conjugation and minimizes steric hindrance with nearby groups. Representative chemical shift data for model compounds are presented.