Lattice Imperfections and Relaxation of Cl NQR in Chloral Iso-Butylhemiacetal

Abstract

The temperature dependence of the S/N ratios of three 35Cl NQR lines (v1, v2 , v3) in chloral iso-butylhemiacetal shows interesting features in the range 77-300 K. 35Cl T1 indicates that above 220 K reorientation of CCl 3 is excited, and this results in a gradual decrease in S/N. The activation energy calculated from 35Cl NQR T1 results is 30 kJ mol-1 for v1 and v2 but 25 kJ mol -1 for v 3 . The difference seems to be attributable to the motion of H in the OH group. A minimum of 35Cl NQR T2 is found around 180 K but 35Cl T1 shows no anomaly. 35Cl T2 determines the S/N ratios in the range between 130-220 K. The line broadening below 130 K is attributable to an inhomogeneity of the electric field gradient at resonant nuclei produced by lattice defects.

Inequivalent Reorientation of the Trichloromethyl Groups in 1,4-Bis(TrichloromethyI) Benzene as Studied by Pulsed 35Cl NQR

“…One of them (molecule 1) is located at a general position, while the center of the other molecule (molecule 2) is at an inver- Since there is no phase transition between 77 K and room temperature, the crystal structure is consistent with the nine line 35C1 NQR spectrum observed between 77 and about 250 K. Since the multiplicity of CCl(21-23) is two, the 35C1 NQR lines of this group are expected to be 2 times as strong as the other six NQR lines. The values of V0 obtained for the CC13 groups in bisTMB are consistent with those reported for the reorientation of CC13 groups in a number of molecu lar crystals [4][5][6][7][8][9][10][11]. The V0 value and the fade out temperature of v3, v5, and v8 are in good agreement with those reported for a related compound, pchlorobenzotrichloride (TMB) [11].…”