Neutron diffraction refinement of trans-2,5-dichloro-1,4-dioxane at 97 K

Abstract

C4H6C1202, Mr = 157.00, triclinic, P1, a = 4.504 (2), b = 5.423 (2), c = 6.592 (3)/~, a = 85.53 (2), /3 = 103.75 (2), y= 106.51 (1) °, V = 149.9 (2)/~3, Z = 1, Dn = 1.739 Mg m -3, an(Be, 002) = 1.0504/~, /z = 0.1924 mm- 1, F(000) = 34.911 fro, T= 97 K, R(F 2) = 0.021, wR(F 2) = 0.036 for 1183 unique reflections. The bond lengths not involving H atoms are in agreement with an earlier X-ray anlaysis to within 0.004 ~. C--C1 bonds are axial and longer than normal; C--O bonds are shorter than normal. The equatorial C--H bond lengths are significantly longer than the axial C--H bonds. Introduction. The X-ray structure analysis of trans- 2,5-dichloro-l,4-dioxane by Altona, Knobler & Romers (1963) is of particular interest because it was one of the first examples of the influence of the anomeric effect on bond lengths. Not only is the molecular conformation of the molecules such that the C--C1 bonds are axial, rather than equatorial, but the C--C1 bond lengths are longer and the C--O bond lengths shorter than the normal values (Sutton, 1958). The purpose of this neutron refinement is to provide nuclear parameters that could be used in a subsequent charge-density analysis.