Isomerism in parabutylchloral; x-ray crystallographic determinations of 2,4,6-tris(1′,1′,2′-trichloropropyl)-1,3,5-trioxanes

-Parabutylchloral (2,4,6-tris(1,1,2-trichloropropyl)-1,3,5-trioxane, C₁₂H₁₅Cl₉O₃) crystallizes in the orthorhombic space groupP2₁2₁2₁ (No. 19) witha=12.165(6),b=9.964(5),c=17.433(9) Å,Z=4. The finalR value is 0.043 for 1667 observed reflections.-Parabutylchloral crystallizes in the orthorhombic space groupPna2₁ (No. 33), witha=12.387(6),b=10.488(5),c=16.605(8) Å,Z=4. The finalR value is 0.047 for 1417 observed reflections.Unlike the geometric isomers- and-parachloral (CCl₃CHO)₃ which exist in boat andcis,cis-chair conformations, the- and-forms of parabutylchloral (CH₃CHClCCl₂CHO)₃ are now shown by X-ray crystallography not to be geometric isomers. Both forms exist incis,cis-chair conformations and the isomerism arises from the chirality of the side chains at the-carbon atoms. In the-form only two of the side chains have the same chirality, but in the-form the chirality at all the-carbon atoms is the same. The X-ray results are supplemented by¹H and¹³C nuclear magnetic resonance spectroscopy and by mass spectrometry.We thank the CSIR (Pretoria) for collecting the diffractometer data, the CSIR and the University of Cape Town for research grants, Dr. M. L. Niven for crystallographic assistance, and Miss C. Angus for preparing parabutylchloral and separating the isomers. The 500 MHz NMR data are courtesy of Mr. Ivan Antonowitz of the CSIR.