Nuclear magnetic resonance spectroscopy is an important tool in the organic lab. Rather than relying on the spectroscopic analysis of a single unknown to learn the technique followed by use of nmr to confirm the structure of products isolated and synthesized, we have developed a systematic approach to teach not only how to process data FIDs, but also how nmr spectroscopy can be used beyond simple structure elucidation. We teach processing nmr spectra (pmr, cmr, DEPT-135, COSY, and HETCOR) in the first semester using data files from the spectra of 4-heptanone. We require that all spectra are correctly processed, including overlaying the cmr and DEPT-135 spectra and that data obtained from the spectra are entered in tables similar to those that appear in textbooks. In the second semester, we teach quantitative analysis through the determination of the mole ratio of a mixture of ethyl ethanoate and methyl propanoate from the pmr spectrum of the mixture. Students learn how to prepare samples, identify which signals are from each compound, and how to use integration to establish the mole ratio of the two esters. Structure determination of a general unknown requires that the compound be purified, an nmr sample prepared, processed, and analyzed. We insist that all spectral data be clearly related to the proposed structure and that literature spectra for the proposed structure be compared to the spectra obtained. This activity builds on the skills developed in the earlier experiments. Finally, the o/p ratio of the product of the nitration of an alkylbenzene is determined by expanding the aromatic region of the pmr spectrum of that product and integrating appropriate signals.

Curriculum for teaching NMR spectroscopy in the organic lab

248th National Meeting (2014)

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