Static and dynamic stereochemistry of HP(O)(BuAr)-Ar-t (Ar = 2-methyl-1-naphthyl) has been studied by a combination of variable-temperature NMR (H-1 and P-13), HPLC, and CD measurements as well as by MM calculations. Two unequally populated stereolabile isomers for each configurational enantiomer have been detected and their anticlinal and synclinal structures assigned. All the four species have been physically separated and identified on a cryogenic HPLC enantioselective column at -83 degrees C. The interconversion barrier measured by dynamic NMR yields essentially the same value as that measured by dynamic HPLC (14.75 and 14.95 kcal mol(-1), respectively).