The unit of chemical shift in NMR is:
Chemical shift is calculated as difference between sample resonance and reference frequency divided by operating frequency, multiplied by ten to sixth, giving parts per million. Raw frequency separation scales with magnetic field strength, so values in hertz vary between 400 and 900 MHz instruments. Expressing as ppm normalizes this dependence, creating field-independent scale reflecting electronic environment. Biological NMR assignments of amide, alpha, aromatic, and methyl protons rely on ppm reporting, ensuring consistent literature values for proteins, nucleic acids, and metabolites regardless of magnet strength used experimentally.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.