Most publications report 15N chemical shifts relative to either nitromethane or liquid ammonia as the 0 ppm reference. Reports on biochemical applications and aqueous solutions almost always use the ammonia scale. Other applications may use either, although the ammonia scale is becoming more common despite IUPAC recommending nitromethane for non-biological systems. NOTE: In older literature, you may find chemical shifts reported relative to nitromethane but on a τ (tau) scale, which has positive numbers upfield (downfrequency, to the right, “normal” for other graphs) instead of the usual σ (sigma) scale with positive numbers downfield (upfrequency, to the left, only in NMR). The easiest way to reference 15N spectra is to use the absolute referencing feature in MNova.
σ scale: Positive values are downfield
τ scale: Positive values are upfield (τ = -σ)
Common chemical shift ranges taken from:
Marek, Radek, et al. “15N NMR spectroscopy in structural analysis: an update (2001-2005).” Current Organic Chemistry 11.13 (2007): 1154-1205.
“Physical Constants of Organic Compounds,” in CRC Handbook of Chemistry and Physics, 106th Edition (Internet Version 2025), John R. Rumble, ed., CRC Press/Taylor & Francis, Boca Raton, FL.
