13C NMR Prediction Online
Free online 13C NMR predictor. Predict carbon NMR chemical shifts from SMILES or structure, and browse experimental 13C spectra from the local library.
Open the interactive predictor: also see 1H NMR prediction. Browse the compound catalog.
What is NMR prediction?
NMR prediction estimates chemical shifts (and often multiplicities) for a molecule from its structure, so you can compare a proposed structure with measured spectra before running an experiment—or assign peaks when experimental data are available.
How ¹³C NMR prediction works on ChemicalTool
You provide a structure—by SMILES, name lookup, or the embedded sketcher—and the service builds a molecular graph, identifies unique carbon environments, and applies machine-learned or rule-based models trained on experimental chemical shift data. The output is a table of predicted δ values (ppm) you can export or compare side-by-side with measured peaks when experimental spectra are available in the catalog.
Prediction is fastest when stereochemistry is explicit in the input SMILES. Tautomers, salts, and mixtures may need the dominant species drawn separately. For ¹³C work, pick the same deuterated solvent you will use in the lab so predicted values sit closer to reality.
Limitations and good practice
Models extrapolate from training data: unusual heterocycles, heavy halogenation, or paramagnetic contaminants can disagree with experiment. Exchangeable protons (OH, NH) are often broad and solvent-sensitive—¹³C predictors may not reproduce lab linewidths. Use prediction to narrow structures, then confirm with a measured spectrum, including solvent residual checks from our residual peak table.
This page does not replace instrument calibration, pulse programs, or 2D experiments. It complements them—especially when you need a quick sanity check before submitting a sample or interpreting a literature structure.
How to use this calculator
- Click Start prediction to open the interactive tool with ¹³C mode selected.
- Enter SMILES or draw the structure; choose solvent if the UI offers it.
- Review predicted shifts and multiplicities (¹³C).
- Search the compound catalog for experimental spectra when available.
- Cross-check solvent peaks using CDCl₃ or DMSO-d₆ impurity tables.
For quick reference without a structure, browse the ¹³C chemical shift table by functional group.
FAQ
What does a ¹³C NMR predictor output?
It lists estimated carbon chemical shifts for each unique carbon environment in your structure, which supports structure confirmation and peak assignment.
Why do carbon shifts move with solvent?
Polar solvents and hydrogen bonding change electron density around carbons. Predictions assume a stated solvent model; experimental shifts should be measured in the same solvent when possible.
Are quaternary carbons included?
Yes—environments without attached protons still receive predicted ¹³C shifts when the model supports them.
Can I compare with ¹H data?
Use the ¹H predictor and experimental library alongside ¹³C results. Heteronuclear correlation (HSQC/HMBC) is still the gold standard in the lab.
Where do reference impurity peaks come from?
Solvent and trace impurity shifts cite Gottlieb (J. Org. Chem. 1997) and Fulmer (Organometallics 2010) compilations linked from our solvent pages.
References & data sources
- NMRShiftDB2 — open experimental NMR chemical shift database.
- Steinbeck, C.; Kuhn, S. NMRShiftDB — nmrshiftdb.nmr.uni-koeln.de
- Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities. J. Org. Chem. 1997, 62, 7512–7515.
- Fulmer, G. R. et al. NMR Chemical Shifts of Trace Impurities. Organometallics 2010, 29, 2176–2179.
- PubChem — compound identifiers and structure depictions (NIH/NCBI).
- Related tools: nmrdb.org (community NMR prediction reference).