Five-Membered Ring Rotations, Pseudorotations, and Hydrogen Bond Exchange Dynamics in the Solid State Studied by NMR Spectroscopy

Abstract

13C CP/MAS NMR studies were carried out on trans-1,2-cyclopentanediol, on 4,4-dimethyl-trans-1,2-cyclopentanediol, and on sulfolane at variable temperatures. The spectra showed evidence of three dynamic solid-state processes: hydrogen bond exchange, ring pseudorotation, and whole molecule rotations about local C2 axes. Fitting of T1ρ data to calculated values of the 13C−1H dipolar interactions allowed differentiation between ring pseudorotations and whole molecule C2 reorientations. Isotopic 1H/2H substitution demonstrated the existence of hydrogen bond exchange processes in the diols. Activation parameters for these processes were derived from both coalescence measurements and the T1ρ measurements.