Conformation Interchange in Nuclear Magnetic Resonance Spectroscopy

Intramolecular dynamics are readily discernible by use of nuclear magnetic resonance spectrometry. A relatively simple laboratory tutorial experiment demonstrating such motion, an internal interchange of conformations, in a readily available nitroaromatic hydrazine (2,2-diphenyl-1-picrylhydrazine in liquid solution) is presented and discussed. Simple computer analysis of the 1H line shapes taken on standard NMR equipment at several temperatures produces the activation energy (as well as the pseudothermodynamic enthalpy, entropy, and Gibbs free-energy changes) for the process. The molecular basis for the molecular motion is easily visualizable.