Application of 1 H NMR selective and biselective relaxation times. III —conformational analysis of quinidine in solution

A relaxation method was applied to quinidine (1) where cross‐relaxations (σ ij ) were obtained by 1 H selective and biselective T 1 measurements and correlation times for molecular reorientation (τ c ) were evaluated from the frequency dependence of the non‐selective T 1. The interproton distances ( r ij ) were estimated using these σ ij and τ c values, and the conformation of 1 was determined by comparing the estimated r ij values with those calculated from the molecular model. The resulting proposed conformation had the following dihedral angles: ∠ C ‐11C‐10C‐3–C‐4 = 150°, ∠ C‐4′C‐9C‐8C‐7 = 50° and ∠ C‐9′C‐4′C‐9C‐8 = 70°. The conformation of the side‐chain (∠ C‐11C‐10C‐3C‐4) is different from the results for the crystal by x‐ray analyses.