Empirical investigation on the reproducibility of ¹³C NMR shift values

Automated NMR spectra interpretation packages are becoming increasingly important especially now that high-throughput synthesis often vastly increases the amount of data to be analyzed in a given time frame. It is vitally important for these interpretation packages to be robust, and this means that it essential to know how the quality of NMR data varies is real life experiments. A practical test concerning the reproducibility of chemical shift information from recorded ¹³C NMR spectra was carried out using eight test substances. Two hundred seventy spectra were contributed from both Academia and Industry and have been subjected to a standardized interpretation. For these spectra the confidence limits of their chemical shifts have been calculated. The standard deviations found vary from 0.2 up to about 2.5 ppm, and the range of values for the shifts reported vary from ±0.7 up to more than ±7 ppm around the respective average shift. Test substances recorded in more polar solvents generally showed higher standard deviations and also exhibit a dependency of the deviation on the chemical shift value.