MolDraw › Chemistry tools › IR Spectrum Viewer
Free IR Spectrum Viewer
Open an infrared spectrum, switch between %T and absorbance, clean the baseline and pick peaks. Each peak gets a likely functional group with a short reason. Compare two spectra on one plot. Your files stay on your device.
or drop it here (drop two files to compare). JCAMP-DX (.jdx, .dx), CSV or TXT (cm-1, intensity), or SPC.
Examples are simulated from typical band positions, so they are free to reuse. Download the sample .jdx (compressed JCAMP-DX).
How to use the IR viewer
- Open your file, or press an example button.
- Press %T or Absorbance to change the y axis. Tick Baseline correction if the background slopes.
- Peaks are picked for you. Move the Threshold slider for more or fewer. Choose Add peak and tap a band to add one.
- Read the table. Each peak shows its best functional group, the usual range and why it fits. Tap a row to shade that band.
- Open a second file or example under Compare with to overlay two spectra.
- Export a PNG for your report, or CSV files of the data and the peak list.
How the group matching works
Each peak is looked up in the same correlation table as the IR spectroscopy chart, built from standard textbook ranges. Then the whole spectrum is used as a check. A carboxylic acid needs a very broad O-H band and a C=O band. An ester needs C=O near 1740 cm-1 and a strong C-O band. Nitro and sulfone groups need both of their bands. Rare groups are only shown first when their checks pass. Anything that fails a check is marked possible.
IR alone rarely proves a structure. Use it with NMR and mass spectra, and treat the fingerprint region (below 1500 cm-1) with care.
Frequently asked questions
Is my spectrum uploaded anywhere?
No. The file is read and drawn inside your browser. Nothing is sent to MolDraw.
Which files can I open?
JCAMP-DX (.jdx, .dx), including compressed data, two-column CSV or TXT (wavenumber, intensity), and SPC files in the common new format. Wavelength in micrometres is changed to cm-1 for you.
How does it name the functional groups?
Each picked peak is looked up in the same correlation table as the MolDraw IR chart. The whole spectrum is then used as a check. For example, a carboxylic acid needs both a very broad O-H band and a C=O band near 1700 cm-1. Matches that fail a check are marked possible.
What does baseline correction do?
It fits a rubber-band line under the spectrum, in absorbance, and takes it away. This removes a sloping or curved background so peak heights compare fairly. The plot is labelled Baseline corrected.
How do I switch between transmittance and absorbance?
Press %T or Absorbance. The tool converts with A = -log10(T), so you can open a %T file and view it as absorbance, or the other way round.
Can I compare two spectra?
Yes. Open a second file under Compare with, or pick an example. Both traces are drawn on the same axis in different colours. Swap makes the second one the main spectrum for peak picking.