436 POLYTYPISM, TWINNING, AND DISORDER IN 2,2-AZIRIDINEDICARBOXAMIDE uniquely determined, because the alternative position is not compatible with the position of /:'5. Q3 may have one of four positions indicated by Q~, Q~i, Q~ii, Q~". If Q3 and P5 are fixed, Q4 is uniquely determined.Thus, only four stacking variants are in agreement with the observed lattice constants of form B.The atomic coordinates of form B (Br/ickner, 1982, deposited data) show that the variants (ii) and (iii) do not exist in form B, whereas both the variants (i) and (iv) are present. This results because:-it was impossible to decide between N and O ato'ms in the Fourier map; -variants (i) and (iv) are almost identical and may be transformed into each other by interchanging O atoms and NH2 groups.More precise information on the occurrence of (i) and (iv) in form B could be obtained from a detailed investigation of the distribution of the intensities in reciprocal space. Possible results are, for instance: -statistical occurrence of (i) and (iv) with approximately equal probabilities; -alternating occurrence of (i) and (iv); -the crystal consists of regions containing either only (i) or only (iv). The volume of the regions of type (i) and the volume of the regions of type (iv) are about the same. In both variants (i) and (iv) the two possible kinds of triples of layers are present. In (i) as well as in (iv) their proportion is 3:1 in favour of the triple existing in form A (see Fig. 3b).Concluding remark. The example discussed is also of interest in OD theory. No structure with a similar stacking of layers has been found so far. The combination of pairs of layers related by a centre of symmetry and pairs of layers related by a fourfold inversion axis is rather unusual.
AbstractThe three isomers of the title compound, Ci4H21NO, are known to have propionate esters with potency rankings 3' > a >/3. The present X-ray analyses have shown their configurations to be: a-base, t-2-CH3, t-3-