Infrared spectroscopy explorer
Read infrared spectra of alcohols, acids, carbonyl compounds, amines, nitriles, alkenes and greenhouse gases against the characteristic ranges, see which bond vibrates for each band and match unknown spectra.
Learning goals
- Describe stretching vibrations
- Describe bending vibrations
- Predict IR absorption count and vibrations for simple molecules
- Identify characteristic functional-group IR absorptions
- Suggest structures from IR spectra
Learning objectives
- Describe stretching vibrations
- Describe bending vibrations
- Predict IR absorption count and vibrations for simple molecules
- Identify characteristic functional-group IR absorptions
- Suggest structures from IR spectra
- Predict characteristic IR absorptions from structure
- Relate polyatomic-gas IR absorption to the greenhouse effect
Simulated infrared spectrum of ethanol, CH₃CH₂OH, with main absorptions near 3340, 2975, 1050 cm⁻¹. The cursor is at 3340 cm⁻¹, transmittance 8%, on the O–H stretch, hydrogen-bonded, inside the range for O–H alcohols and N–H amines.
- Cursor
- 3340 cm-1
- Transmittance
- 8 %
- Absorption
- O–H stretch, hydrogen-bonded
Try this
0 of 4 donePut the cursor on the O–H band of ethanol, then on the O–H band of ethanoic acid. (not done yet)
Both O–H bands are broad because of hydrogen bonding, but the acid's spreads much further, over 2500–3300 cm⁻¹, often hiding the C–H bands.
Find the C=O band in three different compounds. (not done yet)
A carbonyl group always gives a strong, sharp band at 1680–1750 cm⁻¹. Other bands decide whether it is an aldehyde, ketone, acid or ester.
Find every vibration of carbon dioxide, including the one that absorbs nothing. (not done yet)
CO₂ absorbs at only two wavenumbers: its symmetric stretch does not change the dipole, and its two bends share one frequency. The bend at 667 cm⁻¹ lies where Earth emits most strongly, so CO₂ is a greenhouse gas.
Find the reference spectrum that matches each of two unknowns. (not done yet)
Characteristic bands tell you the functional groups. Only the whole spectrum, fingerprint region included, identifies the exact compound.