Crystal structures of synthetic analgetics. IV. Dextropropoxyphene.

The molecular and cystal structure of dextropropoxyphene has been determined by X-ray methods. The crystals are monoclinic, space group P21, with unit cell dimensions a=9.257(2) A; b=9.048(3) A; c=12.074(7) A; beta=93.01(4)degrees. The phase problem was solved by direct methods and the model refined to an R-value of 0.038 for 1799 observed reflections. E.s.d's are, in average, 0.004 A and O.3 degrees in interatomic distances and angles, respectively. The propylamine chain in nearly fully extended, the dihedral angel C4-C5-C7-N being -174.2 degrees. The conformation of this side chain is similar to that in the hydrochloride of the title compound. Thus the proposed bioactive conformation is not preferred by propoxyphene in the crystalline state, as was the case for the free base of methadone.