Crystal Structure and Phase Transformation of Trichloroethylidene Trichlorolactic Ester (Chloralide), Cl3CCHOCOCHOCCl3. An X‐Ray and NQR Study

Trichloroethylidene trichlorolactic ester (Chloralide), Cl3CCHOCOCHOCCl3, crystallizes at room temperature (T ≈︁ 298 K) monoclinic, space group C52h — P21/c, with 4 molecules in the unit cell. The lattice constants are a = (619.94 ± 0.20) pm, b = (1716.3 ± 0.6) pm, c = (1037.0 ± 0.3) pm, β = 95.083° ± 0.010°. The crystal structure was determined with a reliability factor R = 0.044 (1638 symmetry independent reflexes with I > σ(I)). At 343 ≦ T/K ≦ 344 a phase transformation occurs, which shows super heating phenomena. — In the 35Cl‐NQR the 6 line low temperature spectrum 38.178 ≦ v/MHz ≦ 40.178 at T = 77 K is in accordance with the crystal structure. By intensity considerations an assignment of the spectrum of the two different CCl3 groups in the molecule was possible. The high temperature phase of Chloralide shows the fade out phenomenon in the NQR‐spectrum due to hindered rotations of one of the two CCl3 groups. The kinetics of the transformation phase II → phase I is of first order.