Carbon-13 nuclear magnetic resonance of pharmaceutical agents: Benzocaine hydrochloride anesthetics

Carbon-13 nuclear magnetic resonance (CMR) spectra of eleven aromatically substituted benzocaine hydrochloride anesthetics have been measured. Ester carbonyl chemical shifts correlate well with measured carbonyl stretching frequencies and substituent Taft σ_I parameter. Ring substituents show a large effect upon the para carbon CMR chemical shifts which correlate well with Hammett σ's, however no measurable effect on the CMR chemical shifts of the carbonyl bonded diethylaminoethylene portion of the molecule is noted. This evidence suggests that interaction of the polar carbonyl group or the aromatic π system may be important in explaining drug potency in in vivo systems by modifying the configuration of the anesthetic at the receptor site.