Self-Association of N-Methylacetamide Examined by Infrared and NMR Spectroscopies

These spectroscopic experiments investigate polarity and concentration effects on self-association behavior in N-methylacetamide. Inquiry can be limited to the concentration dependence of hydrogen bonding and estimation of dimerization constant (NMR studies) or to the effect of solvent polarity on extent of hydrogen bonding (IR studies). The combined experiments highlight differences between spectral timescales such as signal averaging seen in NMR spectra. Students learn how to obtain physical information about extent of aggregation from spectroscopic data. The experiments are best suited to an advanced undergraduate course. Undergraduate students are introduced to techniques that are relatively unusual in most college laboratory courses, including solution-state IR with solvent subtraction. The NMR experiments require students to use external referencing and to adjust collection parameters to accommodate a range of analyte concentrations spanning three orders of magnitude.