35Cl NQR Relaxation and Hydrogen Bond in Some Chloral Hemiacetals

Abstract

Abstract The crystal structure of chloral ethylhemiacetal has been determined at 291 K: monoclinic, space group C2 2 - P21, Z = 2, a = 854.5(1), b = 594.0(3), c = 853.3(1) pm, β = 108.30(2)°, R = 0.0962. A sharp decrease of the spin lattice relaxation time T1 found for the 35Cl NQR of the CCl3 groups in chloral methyl-, ethyl-and n-heptylhemiacetals is attributed to the onset of reorientation of the group over a potential barrier o f ca. 39, 37, and 32 kJ/mol, respectively. An unusual T1 vs. 1/T curve with a T1 minimum superimposed on the sharp decrease of T1 due to the reorientation was observed for each of the three 35Cl NQR lines of nHp-CH . This phenomenon is tentatively ascribed to a fluctuation of EFG caused by jumping motion of the hydrogen atom s in the OH groups.