Variable Temperature NMR Experiment Studying Restricted Bond Rotation

Abstract

Nuclear magnetic resonance (NMR) spectroscopy has become a cornerstone tool for studying a variety of molecular features in advanced chemistry laboratories. In this experiment, students prepare a pyrrole-β-amide via a one-pot, three-step synthesis and use NMR spectroscopy to confirm its molecular structure. In addition, variable temperature (VT) 1H NMR spectroscopy is used to study the dynamic amide bond, a functional group with restricted rotation about the C-N bond. The VT NMR data allow the students to determine the coalescence temperature associated with the slow equilibrium at room temperature and the corresponding energy barrier (ΔG&daggar;) for the restricted rotation about the C-N bond.