---
title: "IR Spectrum Predictor – Expected Bands from SMILES | MolDraw"
url: https://www.moldraw.com/tools/free-chem-tools/ir-spectrum-predictor.html
description: "Free IR spectrum predictor: paste SMILES or draw a molecule to list its expected IR bands. Example: ethyl acetate C=O 1735–1750 cm⁻¹ plus C–O bands."
lang: en
publisher: Scidart Academy
generated: 2026-10-31
---
[MolDraw](https://www.moldraw.com/) › [Chemistry tools](https://www.moldraw.com/tools/) › IR Spectrum Predictor

# IR Spectrum Predictor

**In short:** Draw a molecule or paste its SMILES. The tool finds its functional groups and lists the IR bands you should expect, with wavenumber range, intensity and shape, on a numbered sketch of the spectrum.

This is a **correlation-chart prediction**: the bands come from standard IR tables for each group, adjusted for conjugation, ring size and substitution. It does not calculate vibrations, so it is not a simulated spectrum. Use it to know which peaks to look for.

**Quick answer:** ethyl acetate, `CCOC(C)=O`, should show a strong ester C=O at 1735–1750 cm⁻¹, strong C–O bands between 1300 and 1000 cm⁻¹ and sp³ C–H at 2850–2960 cm⁻¹, with no O–H or N–H band.

Loading editor…

SMILES (filled from the drawing, or paste your own and press Enter)

[Open in MolDraw](https://www.moldraw.com/)

Examples:

Loading the structure engine…

## How to use the IR spectrum predictor

1. Draw the molecule, or paste a SMILES string and press Enter.
2. The functional groups found are shaded on the drawing and named above it.
3. Each expected band is numbered on the sketch and listed in the table with its range, intensity, shape and the group that causes it.
4. Compare the list with your measured spectrum. A missing strong band (for example no C=O near 1700 cm⁻¹) is as informative as a present one.
5. Copy the list, or download it as CSV or the sketch as SVG.

## Key bands the predictor uses

| Group | Band (cm⁻¹) | Look |
| --- | --- | --- |
| Alcohol O–H | 3200–3550 | strong, broad |
| Carboxylic acid O–H | 2500–3300 | strong, very broad, runs under C–H |
| Primary amine / amide N–H | 3300–3500 (amine), 3150–3370 (amide) | two medium bands |
| Terminal alkyne ≡C–H + C≡C | 3260–3330 and 2100–2140 | strong narrow, then weak |
| Nitrile C≡N | 2240–2260 (conjugated 2215–2240) | medium, sharp |
| Aldehyde C–H | ≈2820 and ≈2720 | two weak bands |
| Anhydride C=O | 1800–1830 and 1740–1775 | two strong bands |
| Acid chloride C=O | 1785–1815 | strong |
| Ester C=O | 1735–1750 (aryl ester 1750–1770, conjugated 1715–1730) | strong |
| Aldehyde C=O | 1720–1740 (conjugated 1685–1710) | strong |
| Ketone C=O | 1705–1725 (conjugated 1666–1700, cyclopentanone ≈1745) | strong |
| Carboxylic acid C=O | 1700–1725 (conjugated 1680–1710) | strong |
| Amide C=O (amide I) | 1650–1690 | strong |
| Nitro N–O | 1500–1560 and 1330–1385 | two strong bands |
| C–O (alcohol, ether, ester) | 1000–1300 | strong |

Conjugation with a C=C or an aromatic ring lowers a C=O band by about 20–30 cm⁻¹. Ring strain raises it. For every band in one searchable table, see the [IR spectroscopy chart](https://www.moldraw.com/tools/free-chem-tools/ir-spectroscopy-chart.html).

Sources: D. L. Pavia, G. M. Lampman, G. S. Kriz & J. R. Vyvyan, *Introduction to Spectroscopy*, 5th ed. (Cengage, 2015); R. M. Silverstein, F. X. Webster, D. J. Kiemle & D. L. Bryce, *Spectrometric Identification of Organic Compounds*, 8th ed. (Wiley, 2014). Exact positions shift with phase (solid, liquid, solution), hydrogen bonding and neighbouring groups.

## What this tool does not do

- It does not compute vibrational frequencies (no DFT or force field). The plot is a sketch, not a simulated spectrum. Real peak positions, widths and heights differ.
- It does not predict the fingerprint region (1500–400 cm⁻¹) band by band. Only the group bands that textbooks list are shown.
- It cannot tell cis from trans alkenes or count exact overtone patterns. Hydrogen bonding, concentration and sample state (KBr, ATR, solution) are ignored.
- Salts, zwitterions, metal complexes and unusual groups are covered only partly. Groups the detector does not know give no band.

**Have a measured spectrum?** Open your JCAMP-DX or CSV file in the free IR viewer to pick peaks and label them.

[Open IR viewer](https://www.moldraw.com/tools/ir-viewer/index.html)

## Frequently asked questions

### Is this a simulated IR spectrum?

No. The tool finds functional groups and lists the bands a textbook correlation chart gives for them. The plot is a sketch that places a dip in the middle of each range. It does not calculate vibrational frequencies.

### Where does a C=O band appear in IR?

Between about 1650 and 1830 cm⁻¹. Saturated ketones absorb near 1715, aldehydes near 1725, esters at 1735–1750, carboxylic acids at 1700–1725, amides at 1650–1690 and anhydrides give two bands near 1820 and 1760 cm⁻¹. Conjugation lowers the band by about 20–30 cm⁻¹.

### How do I tell an alcohol from a carboxylic acid by IR?

An alcohol gives a broad O–H band at 3200–3550 cm⁻¹ and no C=O. A carboxylic acid gives a very broad O–H band from about 2500 to 3300 cm⁻¹ that runs under the C–H peaks, plus a strong C=O near 1710 cm⁻¹.

### Which bands show an aldehyde?

A C=O band near 1725 cm⁻¹ (about 1700 when conjugated) together with two weak C–H bands near 2820 and 2720 cm⁻¹. The 2720 band is the most useful one.

## Related chemistry tools

[IR Spectroscopy Chart (Correlation Table)](https://www.moldraw.com/tools/free-chem-tools/ir-spectroscopy-chart.html)[IR Spectrum Viewer](https://www.moldraw.com/tools/ir-viewer/index.html)[Functional Group Identifier](https://www.moldraw.com/tools/free-chem-tools/functional-group-identifier.html)[13C NMR Predictor](https://www.moldraw.com/tools/free-chem-tools/13c-nmr-predictor.html)[Mass Spectrum Predictor](https://www.moldraw.com/tools/free-chem-tools/mass-spectrum-predictor.html)[Degree of Unsaturation Calculator](https://www.moldraw.com/tools/free-chem-tools/degree-of-unsaturation-calculator.html)

Last updated: October 30, 2026