Acta Crystallographica Section B

Structural Science

Volume 62, Part 3 (June 2006)

research papers

Acta Cryst. (2006). B62, 488-497 [ doi:10.1107/S0108768106000620 ]

S,S-1,2-Dicyclohexylethane-1,2-diol and its racemic compound: a striking exception to Wallach's rule

B. O. Patrick and C. P. Brock

Abstract: The structures of enantiopure S,S-1,2-dicyclohexylethane-1,2-diol and its racemic compound (rac-S,S-1,2-dicyclohexylethane-1,2-diol) have been determined at 295 and 173 K. The crystals of the enantiopure material are more than 4% denser than the crystals of the racemic compound, but the melting points indicate that the crystals of the less dense racemic compound are considerably more stable than those of the racemic conglomerate. This apparent exception to the correlation of crystal density and melting point is explained. The enantiopure crystals have four molecules in the asymmetric unit (Z' = 4). Two of the molecules have the conformation observed for the one independent molecule of the racemic compound and two have a higher energy conformation; the overall P2₁ structure is a perturbed version of a P2₁2₁2₁ structure with Z' = 2. The enantiopure and racemic crystals have the same hydrogen-bonding motif, but the motif in the former appears to be significantly strained. A reason why crystals of enantiopure material might be systematically less dense than crystals of its racemic compound and to be more likely to have Z' > 1 is suggested.

Keywords: racemic compound; Wallach's rule; crystal density; melting point; hydrogen-bonding motif.


	Structure factor file (CIF format) (246.2 kbytes) [ doi:10.1107/S0108768106000620/de5024k98005sup2.hkl ] Contains datablock k98005

	Structure factor file (CIF format) (235.9 kbytes) [ doi:10.1107/S0108768106000620/de5024k00009sup3.hkl ] Contains datablock k00009

	Structure factor file (CIF format) (124.3 kbytes) [ doi:10.1107/S0108768106000620/de5024k98064sup4.hkl ] Contains datablock k98064

	Structure factor file (CIF format) (122.4 kbytes) [ doi:10.1107/S0108768106000620/de5024k00013sup5.hkl ] Contains datablock k00013

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