Pressure- and temperature-dependent proton NMR studies of N,N-dimethylpiperazine ring inversion in the gas phase

Abstract

Gas-phase proton NMR spectra of N-methylpyridine (MPD) obtained at temperatures between 277 and 303 K display exchange-broadened line shapes that are both temperature and pressure dependent. Gas-phase unimolecular activation parameters for the chair to chair ring inversion process are ΔH = 50.6 (0.8) kJ mol -1 , ΔS = 1 (4) J K -1 mol -1 , and ΔG 2 98 =50.2 (0.4) kJ mol -1 . The gas-phase free energy of activation at 298 K is 0.8 kJ mol -1 lower than that obtained in a previous liquid study