Abstract. C8N2C12F4, FW 271.0; monoclinic, P2 I, a = 11-925 (2), b= 5.523 (1), c= 6.785 (1) A, fl=95.09 (2) ° (20°C). Z = 2, Dx= 2.02 g cm -3. The final R index was 5.2% (weighted R 4.0%). No absorption correction was applied (/~= 7.84 cm~). Substantial deformation of the parent 2,7-naphthyridine skeleton results because of the short CI-C1 distance (2.307 A).

The/3-phase crystal structures of unsaturated triacylglycerols (TAGs) have been analyzed. Long spacings and melting points of monounsaturated TAGs such as 16" O. 16 and 16.0" 18 indicate a fi-3C packing mode with a methyl terrace that differs from that of the saturated /3-3 TAGs. In addition to the hydrocarbon chain subcell packing and the methyl terrace structure, the conformation of the oleoyl chain also has to be considered. This conformation is analyzed in connection with the symmetry relation between the two half-layers on either side of the plane through the double bonds. Geometric analysis shows four possibilities, which have been explored further by means of energy minimization computations. In these calculations the structure of the oleoyl chain, in its crystalline environment, has been optimized while taking all relevant intramolecular and intermolecular forces into account. Though the calculations reveal relatively small energy differences between the four possibilities, the most likely structure can still be identified. On the basis of the results obtained for the monounsaturated TAGs, proposals for the crystal structures of diunsaturated (e.g., 0 9 18. O) and triunsaturated (e.g., 0" 0" O) TAGs are briefly outlined.

To reveal the structure ofβ′ triacylglycerols in detail, LML (C12C14C12) was purified by a zone‐melting procedure, and twinned crystals ofβ′ stable LML were obtained from a melt,β′ LML crystallizes in the monoclinic space group C2, with eight molecules in the unit cell. A powder X‐ray diffraction study of solid compounds of 1:1 mixtures of selected triacylglycerols led to the conclusion that the triacylglycerol molecules in theβ modification have a 1,2 chair‐conformation (i.e., the fatty acid chains on glycerol positions 1 and 2 are adjacent, with the chain on the 3‐position forming the back rest of the chair). Packing studies and the positions of two‐fold axes and two‐fold screw axes in the unit cell require that the molecules are bent at the glycerol site. The fatty acid chains make an angle of 25° with the long axis of the unit cell. Electron micrographs and precession photographs indicate that the twinning results from the stacking of a large number of thin crystalline platelets in two distinct orientations.

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