Relative Population of S-Form and F-Form Conformers of Bryonolic Acid and Its Derivatives in Equilibrium in CDCl₃ Solutions

Abstract

Relative populations of S-form (D–E rings: boat–boat form) and F-form (D–E rings: chair–chair form) conformers, in equilibrium in CDCl₃ solutions, of 20 derivatives (2—21) of bryonolic acid (D:C-friedoolean-8-en-3β-ol-29-oic acid) (1) were calculated from NMR spectral data (J-values and chemical shifts), with the aid of molecular mechanic calculation using a MM2/CONFLEX program system. The principal deciding factor of the population ratio was found to be whether the functionality at C-29 is trigonal or tetrahedral; the S-form : F-form was 0 : 100—32 : 68 for the “trigonal” type and 48 : 52—100 : 0 for the “tetrahedral.” The reliability of the results is discussed.