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🌈 FTIR Functional Group Match Helper

Find candidate functional groups matching an observed FTIR peak wavenumber, based on standard IR correlation ranges.

Observed Wavenumber cm⁻¹

Possible Matches

💡 Note: IR correlation ranges commonly overlap (e.g. 1715 cm⁻¹ fits both ketone and carboxylic acid C=O stretches) — a single peak rarely gives a definitive answer on its own. Always interpret candidate matches alongside the rest of the spectrum, peak shape/width, and complementary data (NMR, MS) before assigning a structure.

📖 Example: A peak at 1715 cm⁻¹ matches the typical range for aldehyde/ketone C=O stretch (1705-1725 cm⁻¹) and carboxylic acid C=O stretch (1700-1725 cm⁻¹) — the surrounding spectrum (e.g. presence of a broad O-H band) would help distinguish between them.

Frequently asked questions

Why do I get multiple matches for one wavenumber?

Many functional groups absorb in overlapping wavenumber ranges — for example, ketone, aldehyde, and carboxylic acid C=O stretches all fall between roughly 1700-1750 cm⁻¹. A single peak position is rarely enough to distinguish between them; peak shape, intensity, and the presence of other supporting bands (like a broad O-H for acids) are needed for a confident assignment.

What's the 'fingerprint region' and why is it harder to interpret?

The region below about 1500 cm⁻¹ (down to 400 cm⁻¹) contains complex, overlapping vibrations unique to each molecule's specific structure, making individual peaks hard to assign to single functional groups. It's called the fingerprint region because, while hard to interpret band-by-band, the overall pattern is often unique enough to match against a reference spectral library.

Can this replace comparing against a reference spectrum?

No — this tool gives a quick first-pass check against standard correlation ranges, useful for narrowing down possibilities. Confirming a functional group assignment, especially for publication or regulated work, should involve comparison against authentic reference spectra or complementary techniques like NMR and mass spectrometry.

Accuracy & how this is derived

Derivation: Direct reference lookup against standard published IR correlation ranges for common functional group vibrations — no calculation is performed.

Validated against: Standard IR correlation table ranges consistent with widely used spectroscopy references (e.g. Silverstein, Webster & Kiemle, Spectrometric Identification of Organic Compounds; Pavia, Introduction to Spectroscopy).

⚠️ For educational and research support only — verify critical results independently before use in regulated, clinical, or publication-bound work.

✔ Last updated: July 2026 · Report an error

Using IR correlation tables to assign functional groups

Infrared spectroscopy identifies functional groups by matching observed absorption peaks to well-established wavenumber ranges characteristic of specific bond vibrations, such as carbonyl stretches near 1700-1750 cm-1 or broad hydroxyl stretches above 3200 cm-1. Because many functional groups absorb in overlapping ranges, a single peak position is rarely sufficient on its own — experienced spectroscopists cross-reference peak shape, relative intensity, and the presence of supporting bands elsewhere in the spectrum before committing to a structural assignment, making a quick correlation lookup a useful first step rather than a final answer.