NMR Chemical Shifts of Emerging Green Solvents, Acids, and Bases for Facile Trace Impurity Analysis

The straightforward identification of impurity signals in nuclear magnetic resonance (NMR) spectra is imperative for the structure elucidation and signal assignment of synthetic products and intermediates. To keep pace with the emergence of novel green solvents and auxiliary compounds (e.g., acids and bases), NMR impurity tables and databases must be regularly updated. This study reports the residual ¹H and ¹³C NMR chemical shifts of 42 green solvents, acids, and bases in eight NMR solvents, namely, dimethylsulfoxide-d₆, chloroform-d, D₂O, CD₃OD, CD₃CN, acetone-d₆, tetrahydrofuran-d₈, and toluene-d₈. The multiplicities and coupling constants of ¹H signals are also determined herein. The analysis of the recorded NMR spectra provides important information regarding the reactivity or multicomponent nature of the green solvents, acids, and bases. Herein, the results of this study are combined with earlier reports on residual NMR impurities to form a comprehensive database. This database forms the basis of an online interface (http://www.nmrimpurities.com) through which users can browse solvent spectra and search for signals of unknown origins to easily identify residual impurities in NMR spectra.