Kinetics of Internal Rotation of N,N-Dimethylacetamide: A Spin-Saturation Transfer Experiment

Abstract

A new experiment for the undergraduate physical chemistry laboratory is presented for the application of dynamic nuclear magnetic resonance (DNMR) spectroscopy to the study of internal rotation kinetics in N, N -dimethylacetamide (DMA). Spin-lattic relaxation times (T1) were measured by the inversion recovery method and rates of internal rotation about the amide bond in DMA were measured bya spin-saturation transfer method in the temperature range 5-23°C. The activation parameters, Delta H 298 = 70.6 + 1.4 kJ/mol and Delta S 298 = -11 + 5 kJ/mol, were determined from the temperature dependence of the rate of internal rotation. Through the temperature range used in the present work is quite narrow compared with the line-shape analysis experiment, the derived thermodynamic data are in excellent agreement with more extensive measurements.