How to read an NMR spectrum (¹H and ¹³C)
A complete, illustrated guide to interpreting proton and carbon-13 NMR: what each feature means, reference tables, annotated spectra with expanded multiplets and integrals, DEPT, three worked unknowns and a quiz.
On this page
What an NMR spectrum shows
Nuclear magnetic resonance (NMR) spectroscopy detects nuclei such as ¹H and ¹³C in a strong magnetic field. Each chemically different nucleus resonates at a slightly different frequency, reported as the chemical shift δ in ppm relative to tetramethylsilane (TMS, δ = 0). The x-axis runs from high δ on the left (downfield, deshielded) to low δ on the right (upfield, shielded).
A ¹H NMR spectrum gives four pieces of information: (1) number of signals = number of proton environments, (2) chemical shift = type of environment, (3) integration = relative number of H, (4) splitting = number of neighbouring H.
How to read a ¹H NMR spectrum in 6 steps
- Get the formula and degree of unsaturation from MS (formula finder) and the degree of unsaturation calculator.
- Count the signals → number of different H environments (equivalent protons give one signal).
- Read each chemical shift with the table below (e.g. 0.9–1.8 alkyl, 2.0–2.7 next to C=O or aromatic ring, 3.3–4.5 next to O or halogen, 6.5–8.5 aromatic, 9–10 aldehyde).
- Use the integrals to find the ratio of H, then scale to the formula's total H.
- Read the splitting (n+1 rule): a signal split into n+1 lines has n equivalent neighbouring H on adjacent carbons.
- Assemble fragments (e.g. a 2H quartet + 3H triplet = ethyl group CH₂CH₃), then check the full structure with the structure-to-NMR predictor.
Chemical shift: ¹H NMR chemical shift table
Electronegative atoms and π systems pull electron density away from a proton (deshielding), moving it downfield (higher δ). Aromatic and aldehyde protons are further deshielded by ring currents and C=O anisotropy.
| Proton type | δ (ppm) | Example |
|---|---|---|
| TMS reference | 0.0 | Si(CH₃)₄ |
| Alkyl C–H (CH₃, CH₂, CH) | 0.9–1.8 | CH₃ of ethyl, 0.9–1.3 |
| Allylic, benzylic, α to C=O | 1.7–2.7 | CH₃C=O 2.0–2.2; ArCH₃ 2.3 |
| Alkyne ≡C–H | 2.0–3.0 | terminal alkyne ~2.5 |
| C–H next to N | 2.2–2.9 | CH₂NH₂ ~2.7 |
| C–H next to halogen | 2.5–4.5 | CH₃Cl 3.05; (CH₃)₂CHCl 4.17 |
| C–H next to O (alcohol, ether, ester) | 3.3–4.5 | OCH₃ 3.3–3.9; OCH₂ of ester ~4.1 |
| Vinylic =C–H | 4.5–6.5 | alkenes |
| Aromatic Ar–H | 6.5–8.5 | benzene 7.36 |
| Aldehyde CHO | 9–10 | ~9.7 |
| Carboxylic acid COOH | 10–13 (broad) | ~11–12 |
| Alcohol O–H / amine N–H | 0.5–5 (variable, broad) | depends on solvent and concentration |
| Phenol O–H | 4–8 | variable |
Integration: how many protons?
The area under each signal is proportional to the number of protons producing it. Spectrometers display an integral curve (the stepped line in the figures) or a number under each peak. Integrals give ratios: for ethyl acetate the steps are 2 : 3 : 3, which already adds up to the 8 H of C₄H₈O₂. If the ratio adds up to fewer H than the formula, multiply (e.g. 1 : 1.5 → 2 : 3).
Splitting and the n+1 rule
Protons on adjacent carbons (three bonds apart, H–C–C–H) couple through the bonding electrons. A proton with n equivalent neighbouring protons is split into n + 1 lines with intensities from Pascal's triangle. Equivalent protons do not split each other, and O–H/N–H protons usually do not couple because they exchange rapidly.
| Neighbours (n) | Lines | Name | Intensities |
|---|---|---|---|
| 0 | 1 | singlet (s) | 1 |
| 1 | 2 | doublet (d) | 1:1 |
| 2 | 3 | triplet (t) | 1:2:1 |
| 3 | 4 | quartet (q) | 1:3:3:1 |
| 4 | 5 | quintet (pentet) | 1:4:6:4:1 |
| 5 | 6 | sextet | 1:5:10:10:5:1 |
| 6 | 7 | septet | 1:6:15:20:15:6:1 |
Coupling constants (J values)
The spacing between lines of a multiplet, in hertz, is the coupling constant J. It does not change with magnet strength, so it tells you about geometry.
| Relationship | Typical J (Hz) |
|---|---|
| Vicinal H–C–C–H, free rotation (sp³) | 6–8 |
| Alkene, trans | 11–18 |
| Alkene, cis | 6–14 |
| Alkene, geminal (=CH₂) | 0–3 |
| Aromatic ortho | 6–10 (≈ 8) |
| Aromatic meta | 1–3 |
| Aromatic para | 0–1 |
| Aldehyde CHO–CH | 1–3 |
When a proton has two different sets of neighbours with different J values the n+1 rule is applied twice, giving a doublet of doublets (dd), doublet of triplets (dt), and so on. Overlapping, complex patterns are reported as multiplets (m).
Chemical equivalence: how many signals?
Protons are equivalent if they are interchanged by symmetry (a mirror plane, a rotation axis) or by fast rotation. Replace each H in turn with a test group "X": if you get the same compound, those H are equivalent. Examples: ethane (1 signal), propane (2), 2-chloropropane (2), ethyl acetate (3), toluene (4: CH₃ plus ortho, meta and para ring H, although the ring H often overlap). Diastereotopic CH₂ protons next to a stereocentre are not equivalent and can give separate signals.
How to read a ¹³C NMR spectrum
Routine ¹³C spectra are proton-decoupled, so every unique carbon gives a single line; there is no splitting, and peak heights are not reliable for counting (quaternary carbons are weak). Count the lines to get the number of carbon environments and use the shift ranges:
| Carbon type | δ (ppm) |
|---|---|
| sp³ alkyl (CH₃, CH₂, CH) | 0–50 |
| C–N | 30–65 |
| C–O (alcohols, ethers, esters) | 50–90 |
| Alkyne C≡C | 65–90 |
| Alkene C=C | 100–150 |
| Aromatic C | 110–160 |
| Nitrile C≡N | 115–125 |
| Acid, ester, amide C=O | 160–185 |
| Aldehyde, ketone C=O | 190–220 |
DEPT basics: CH, CH₂ or CH₃?
DEPT (Distortionless Enhancement by Polarization Transfer) experiments edit a ¹³C spectrum by the number of attached H. DEPT-90 shows only CH carbons. DEPT-135 shows CH and CH₃ pointing up and CH₂ pointing down. Quaternary carbons (no H) are absent from both, so comparing with the normal ¹³C spectrum identifies them.
Worked examples
Example 1: C₄H₈O, IR 1717 cm⁻¹
DoU = 1 and IR shows a ketone C=O. The 2H quartet and 3H triplet share J = 7.3 Hz → an ethyl group; the CH₂ at 2.44 is next to C=O. The 3H singlet at 2.14 is a methyl on C=O with no neighbours. Answer: 2-butanone, CH₃COCH₂CH₃, confirmed by four ¹³C lines including 209 ppm (Figure 4).
Example 2: C₈H₁₀
DoU = 4 → a benzene ring is likely. 5 aromatic H → monosubstituted ring. Quartet + triplet = ethyl; CH₂ at 2.65 is benzylic. Answer: ethylbenzene. DEPT (Figure 5) shows one quaternary aromatic C, three CH, one CH₂ and one CH₃.
Example 3: C₃H₇Cl
Two signals: 1H septet at 4.17 and 6H doublet at 1.52 (Figure 2). Septet + 6H doublet = isopropyl; CH at 4.17 bears Cl. Answer: 2-chloropropane (1-chloropropane would give three signals: t 3.5, sextet 1.8, t 1.0).
Solvent, water and D₂O
Spectra are run in deuterated solvents (CDCl₃, DMSO-d₆, D₂O) so the solvent does not swamp the sample; residual CHCl₃ appears at 7.26 ppm. Water shows up as a singlet at about 1.56 ppm in CDCl₃ (3.33 in DMSO-d₆). Shaking the sample with a drop of D₂O exchanges O–H and N–H protons for deuterium, so their signals disappear, a quick way to identify them.
Practise with MolDraw
Draw any structure and predict its spectrum with structure to NMR or SMILES to NMR; in the editor the NMR Analyser plugin adds COSY, HSQC and HMBC. Combine NMR with the IR guide, IR chart and the mass spectrum guide to solve full structures.
Practice quiz
Tap an answer to check it.
1. A 2H quartet and a 3H triplet with the same J value indicate…
CH₂ (3 neighbours → quartet) next to CH₃ (2 neighbours → triplet) = ethyl.
2. A proton has six equivalent neighbours. Its signal is a…
n + 1 = 7 lines = septet, as for the CH of an isopropyl group.
3. A singlet at 9.7 ppm most likely belongs to…
Aldehyde protons appear at 9–10 ppm.
4. How many ¹H NMR signals does 2-chloropropane give?
The two CH₃ groups are equivalent (one signal) plus the CH: two signals.
5. In a DEPT-135 spectrum, a negative peak is a…
DEPT-135: CH₂ down; CH and CH₃ up; quaternary absent.
6. A ¹³C line at 208 ppm indicates…
Above ~190 ppm → aldehyde or ketone carbonyl.
7. Integrals of 1 : 1.5 for a compound with 10 H in two signals correspond to…
1 : 1.5 = 2 : 3; scaled to 10 H gives 4H and 6H.
Frequently asked questions
How do I interpret a 1H NMR spectrum?
Count the signals (proton environments), read each chemical shift to identify the environment, use the integrals for the number of H, and use the splitting (n+1 rule) to find the number of neighbouring H. Then join the fragments into a structure consistent with the molecular formula.
How do you interpret a 13C NMR spectrum?
Each line is a unique carbon environment (spectra are proton-decoupled, so there is no splitting). Use shift ranges: 0–50 sp³, 50–90 C–O, 100–160 alkene/aromatic, 160–185 acid/ester/amide C=O, 190–220 aldehyde/ketone C=O. DEPT tells you how many H each carbon carries.
What does an NMR peak at 0 ppm mean?
δ = 0 is the reference signal of tetramethylsilane (TMS) added as an internal standard. It is not part of your compound.
What are 5 peaks on NMR called?
A quintet (or pentet), intensities 1:4:6:4:1, from a proton with four equivalent neighbouring protons.
What are 6 peaks called in NMR?
A sextet, intensities 1:5:10:10:5:1, from a proton with five equivalent neighbours (e.g. the middle CH₂ of a propyl group).
What is the n+1 rule?
A proton with n equivalent neighbouring protons on adjacent carbons appears as n + 1 lines: 0 → singlet, 1 → doublet, 2 → triplet, 3 → quartet.
Why do we use D2O in NMR?
D₂O is a deuterated solvent with no ¹H signal, and a "D₂O shake" exchanges O–H and N–H protons for deuterium so their peaks disappear, identifying them.
Does water show up on NMR?
Yes. Traces of water give a singlet near 1.56 ppm in CDCl₃, 3.33 ppm in DMSO-d₆ and 4.79 ppm in D₂O (as HDO).
What does DEPT-135 show?
CH and CH₃ carbons as positive peaks, CH₂ carbons as negative peaks; quaternary carbons are absent.
References and data sources
- Pavia, Lampman, Kriz & Vyvyan, Introduction to Spectroscopy, 5th ed., Cengage, ch. 5–7.
- Silverstein, Webster & Kiemle, Spectrometric Identification of Organic Compounds, 8th ed., Wiley, ch. 3–4.
- SDBS Spectral Database for Organic Compounds (AIST): ¹H/¹³C NMR of ethyl acetate, 2-butanone, 2-chloropropane, ethylbenzene.
- Fulmer, G. R. et al. "NMR Chemical Shifts of Trace Impurities", Organometallics 2010, 29, 2176 (water and solvent residual peaks).
- Reich, H. J. Structure Determination Using NMR, University of Wisconsin (chemical shift and coupling constant tables).
Spectra on this page are redrawn schematically from the reference data above (peak positions and approximate relative intensities) for teaching; check the original database entry before citing exact intensities.