BRAINCAKEIdentifying O-H and N-H Protons with D2O
Protons in O-H (alcohols, carboxylic acids) and N-H (amines, amides) groups are hard to identify from a 1H NMR spectrum:
• their chemical shift varies with solvent, concentration and hydrogen bonding, so the data sheet gives a wide range (for example R-OH 0.5-6.0 ppm)
• they usually appear as a broad singlet, because they exchange rapidly between molecules and so do not split, or get split by, neighbouring protons
To confirm which peak is O-H or N-H, the spectrum is run twice:
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Key terms in this lesson
- singlet
- An NMR peak that is not split into sub-peaks, because there are no protons on an adjacent carbon atom.
- chemical shift
- The position of a peak in an NMR spectrum, measured in parts per million (ppm) relative to the TMS reference peak at 0 ppm.
More in NMR Spectroscopy
- Deuterated Solvents
- 13C NMR Spectroscopy
- Interpreting 13C NMR Spectra
- 1H NMR Spectroscopy
- Relative Peak Areas
- Spin-Spin Splitting
- The n+1 Rule
- Combining Techniques to Deduce Structures
All 12 lessons in NMR Spectroscopy · All OCR A-level Organic Chemistry topics