From the Archives: Nudelman's Essential NMR Analysis Reference Guide

In the world of organic chemistry, there exists a manuscript that silently but profoundly influences our daily work. Crafted by Nudelman in 1997, this unassuming publication has been cited over 5000 times and is a tool in the arsenal of nearly every organic chemist. Its content is prominently displayed on laboratory walls across the globe. The manuscript in question is none other than the celebrated 'NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities,' featured in the Journal of Organic Chemistry.[1,2] Nudelman's paper has been the go-to reference guide for NMR analysis for over 25 years.

The manuscript's importance lies in its practicality. NMR is a fundamental tool for chemists, and the ability to quickly and accurately identify trace impurities in NMR can save countless hours of troubleshooting and potentially lead to more accurate results. Here are a few reasons why this paper is so underappreciated yet indispensable:

1. Practical Utility: As mentioned, the paper provides NMR data for common laboratory solvents and contaminants. This information is invaluable for interpreting NMR spectra and diagnosing issues in experiments.

2. Time-Saving: Identifying impurities or solvent traces in NMR spectra can be time-consuming and frustrating. Having a reference like this at hand can streamline the process.

3. Avoiding Costly Mistakes: Mistaking a solvent peak for a reaction product can lead to incorrect conclusions or wasted effort. This manuscript helps prevent such errors.

4. Teaching Tool: It's not just a resource for seasoned chemists. It's also an excellent teaching tool for students learning to interpret NMR spectra and understand the importance of solvent purity.

5. Universal Applicability: The fact that this resource covers common solvents used globally makes it universally applicable, regardless of the specific subfield of chemistry.

6. Longevity: The paper's enduring relevance speaks to the quality of the data and the care taken in its compilation. Chemistry is a field where certain fundamentals remain unchanged for decades.

During the course of my doctoral studies, this manuscript became my steadfast ally. In the early days, it rescued me from the perplexing sight of a huge singlet appearing around ~2.1 ppm in the 1H NMR spectrum, promptly identifying it as acetone (or possibly acetonitrile!). This revelation indicated that the solvent used for NMR tube washing had not undergone sufficient drying. Later on, the manuscript unveiled the true identity of a suspected reaction by-product: 'grease' (notably, two distinct types of grease were analysed in the paper). On other occasions, it unmasked the presence of non-volatile solvents, signaling the need for further purification. Most frequently, the manuscript's data tables confirmed the presence of an unwelcome guest, ethyl acetate, hinting that the reaction flask required more time on the rotary evaporator.

'Nudelman's NMR analysis reference guide is an unsung hero from the archives'

In the grand tapestry of the chemistry archives, this manuscript stands as a humble and often overlooked hero. While the Journal of Organic Chemistry paper boasts over 5000 citations and its Organometallics counterpart exceeds 4000, the true measure of its impact transcends these numbers. Countless research endeavors have been aided by its NMR data tables, likely numbering in the millions, making it a ubiquitous but unheralded presence. It appears that this paper has become so deeply ingrained in research and analysis practices that many groups reporting no longer feel the need to include it in their reference lists.

In conclusion, this underappreciated manuscript from the chemistry archives serves as a reminder that the most enduring contributions to science are often found in the unassuming pages of a reference, quietly but persistently guiding the hands of researchers toward greater discoveries.

References

1. Gottlieb H.E., Kotlyar V., Nudelman, A. NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities. J. Org. Chem. 1997, 62, 7512–7515.

2. We should also mention a subsequent reference authored by some members of the same team, published in Organometallics: Fulmer G. R., Miller A. J. M., Sherden, M. H., Gottlieb H. E., Nudelman A., Stoltz B. M., Bercaw J.M., Goldberg, K. I. NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist. Organometallics 2010, 29, 2176–2179. This companion piece extends the scope of the original paper by analyzing a broader range of contaminants and employing a variety of deuterated NMR solvents.

3. A further updated guide, with particular relevence to industrial processes, has also been published: Babij, N. R. et al. NMR Chemical Shifts of Trace Impurities: Industrially Preferred Solvents Used in Process and Green Chemistry. Org. Process Res. Dev. 2016, 20, 661–667.