Molecular conformations of dibucaine in solution as determined by NMR lanthanide-induced shifts and conformational energy calculations

Proton lanthanide‐induced shifts (LIS) were measured for Yb(fod)3‐dibucaine complexes in CDCl3 solution. The data were used in conjunction with empirical energy calculations to determine the preferred conformations of dibucaine. The energy calculations and the LIS analysis were in agreement in showing that the plane of the amide group makes an angle of approximately 60° with the plane of the quinoline ring, and also that the two carbon‐carbon bonds between the amide group and the tertiary amine nitrogen are both in gauche configurations. Energy calculations showed that the diethyl tertiary zmine group has very restricted conformational freedom owing to internal steric constraints. The butyl ether group has considerable flexibility but is forced out of the plane of the quinoline ring by steric effects.