Infrared Spectroscopy – Functional Groups, Bond Vibrations and Greenhouse Gases
ChemistryOrganic ChemistryAges 16–17
Loading…
Sign in to playView schematic IR spectra from 4000 to 500 cm⁻¹ for ten organic compounds, move a cursor to read the bands and compare them with a correlation table (O–H, N–H, C–H, C≡N, C=O, C=C, C–O, fingerprint region), then try a quiz on identifying functional groups. Other screens model a bond stretching like a spring, IR absorption by CO₂, H₂O and CH₄ in the greenhouse effect, and a UV-visible spectrum linking absorbed and observed colour.
Lesson: Infrared spectroscopy and identifying functional groups
What it shows
Infrared radiation makes covalent bonds vibrate. A bond absorbs only at the frequency of its own stretching or bending vibration, which depends on the bond strength and the masses of the atoms, so each functional group absorbs in a typical range of wavenumbers: a broad O–H band at 3230–3550 cm⁻¹ in alcohols, a very broad O–H at 2500–3300 cm⁻¹ in carboxylic acids, and a strong C=O at 1680–1750 cm⁻¹. The fingerprint region below 1500 cm⁻¹ is unique to each compound. The same physics explains why CO₂, H₂O and CH₄ are greenhouse gases while N₂ and O₂ are not.
How to use
On the View IR spectrum screen, choose a Molecule, tick Correlation table and move the cursor over the spectrum to read wavenumbers; use Compare with to overlay a second compound. On Functional group quiz, read the unknown spectrum and press a family button; Next question gives a new one. On Bond vibration, tune the IR wavenumber to the absorption line and change the Force constant k. Then explore Greenhouse gases and UV-visible and colour.
Parameters you can change
- Screen View IR spectrum, Functional group quiz, Bond vibration, Greenhouse gases, UV-visible and colour
- Molecule shown hexane, hex-1-ene, methylbenzene (toluene), ethanol, propanal, propanone (acetone), propanoic acid, ethyl ethanoate (ethyl acetate), propan-1-amine, ethanenitrile (acetonitrile)
- Compare with (none), hexane, hex-1-ene, methylbenzene (toluene), ethanol, propanal, propanone (acetone), propanoic acid, ethyl ethanoate (ethyl acetate), propan-1-amine, ethanenitrile (acetonitrile)
- Vibrating bond C–H, C–D (deuterium), O–H, N–H, C–O, C=C, C=O, C≡N
- Gas Carbon dioxide (CO₂), Water vapour (H₂O), Methane (CH₄), Nitrogen and oxygen (N₂, O₂)
- Coloured species (UV-visible) Manganate(VII) ion MnO₄⁻ (KMnO₄), [Cu(H₂O)₆]²⁺ ion (CuSO₄ solution), [Cu(NH₃)₄(H₂O)₂]²⁺ complex, Dichromate(VI) ion Cr₂O₇²⁻, β-carotene (in carrots), Chlorophyll a
Questions to explore
- How can you tell an alcohol from a carboxylic acid using only the O–H band?
- Which band distinguishes an aldehyde from a ketone, and where does it appear?
- Why do CO₂ and H₂O absorb infrared radiation while N₂ and O₂ do not?
