NMR solvent impurities

Every tabulated signal in the chosen solvent that lies within the tolerance of your shift is a candidate, nearest first. A signal tabulated as a range, such as a multiplet, counts as a perfect match anywhere inside it. Where two signals are equally close, the common laboratory solvents come before the rarer reagents. An impurity always shows all of its signals at the right ratio, so each row lists the compound's other signals in the same solvent: if they are missing from your spectrum, it is something else.

The default tolerances, ±0.03 ppm for ¹H and ±0.3 ppm for ¹³C, cover the scatter between the three papers. Concentration, temperature and the referencing of your spectrum can move signals further; widen the tolerance when nothing matches.

The water signal and the OH and NH signals of the impurities depend on temperature, concentration and anything in the sample that accepts or donates a hydrogen bond. The tables give them at room temperature for traces in the pure solvent; in a real sample they can sit several tenths of a ppm away. In D₂O, Gottlieb gives the HDO signal as δ = 5.060 − 0.0122 T + 2.11 × 10⁻⁵ T², with T in °C.

• H. E. Gottlieb, V. Kotlyar, A. Nudelman, J. Org. Chem. 1997, 62, 7512–7515, doi:10.1021/jo971176v.
• G. R. Fulmer, A. J. M. Miller, N. H. Sherden, H. E. Gottlieb, A. Nudelman, B. M. Stoltz, J. E. Bercaw, K. I. Goldberg, Organometallics 2010, 29, 2176–2179, doi:10.1021/om100106e.
• N. R. Babij, E. O. McCusker, G. T. Whiteker et al., Org. Process Res. Dev. 2016, 20, 661–667, doi:10.1021/acs.oprd.5b00417.

Gottlieb measured CDCl₃, acetone-d₆, DMSO-d₆, C₆D₆, CD₃CN, CD₃OD and D₂O. Fulmer repeated them and added THF-d₈, CD₂Cl₂, toluene-d₈, C₆D₅Cl and TFE-d₃, gases and reagents of organometallic chemistry. Babij added the solvents that process chemistry prefers, such as 2-MeTHF, CPME and isopropyl acetate, in six of the solvents. All three ran their spectra at room temperature, 22 to 26 °C, with shifts relative to TMS; ¹H in D₂O is relative to sodium 3-(trimethylsilyl)propanesulfonate. Where the papers overlap, Fulmer's value is shown. Every value was checked against a second copy of the same data, the printed table against the supporting information; the few misprints this found are corrected, for example the 2-propanol CH₃ in CD₃OD at 1.15 ppm, not 1.50.

Signum labels these peaks after peak picking when a spectrum names its solvent and every signal of a compound is found with its multiplet resolved, and the NMR predictor draws its residual solvent lines from the same tables.