Determination of Equilibrium Constants using NMR Spectroscopy

In this laboratory exercise we will measure the equilibrium constant for the cis-trans isomerism about a peptide bond involving the amino acid L-Proline. This will be accomplished by determining the relative concentrations of each isomer using key proton signals in a Nuclear Magnetic Resonance (NMR) spectrum of a solution of an N-Acetyl derivative of the amino acid, which will serve as a model for peptide bonds involving Proline. In each case, the relative concentration of the equilibrium species can be determined from the NMR signal strength. The relative concentrations can then be leveraged to determine the desired equilibrium constant. This data can then be used to determine   for the isomerization reaction. We will consider the equilibrium in both polar and non-polar solvents as well as in aqueous solutions of various pH's.