Exploring 1H–15N Two Dimensional Nuclear Magnetic Resonance Correlations in an Advanced Organic Spectroscopy Course

At Cal Poly, San Luis Obispo we offer an upper division spectroscopy laboratory course that introduces our majors to the characterization of organic molecules using advanced techniques. The traditional format includes analysis of mass spectral data, 1H and 13C Nuclear Magnetic Resonance (NMR) data, and a variety of two- dimensional (2D) experiments such as 1H– 1H COSY, 1H– 13C HMQC, 1H– 13C HMBC, and NOESY. Our recent efforts have been to expand this curriculum into the characterization of nitrogen containing molecules. Unfortunately, the low relative abundance and gyromagnetic ratio of nitrogen makes one- dimensional (1D) nitrogen NMR difficult to obtain in the timeframe of an undergraduate laboratory. The advantage of the 1H– 15N HMBC and HSQC indirect detection method is that students are able to obtain data in a three- hour laboratory setting. Caffeine is an excellent choice for this experiment in that it is readily available and conveniently links to previously published experiments in natural products extraction. Another advantage of caffeine is that it gives 2D nitrogen correlations within an acceptable timeframe, which allows for both a classroom discussion of nitrogen chemical shifts and the determination of molecular structure.