16 IR spectroscopy

what is the effect of IR radiation on covalent bonds?

vibrate (stretching and bending)

different bonds absorb different frequencies depending on bond strength and atoms

3 main atmospheric greenhouse gases and what bonds do they contain?

CO2, C=O bond

CH4, C-H bond

H2O vapour, O-H bonds

these bonds absorb IR radiation

how can alcohols be identified using IR spectroscopy?

3200-3600cm -1 (O-H)

broad peak

how can aldehydes and ketones be identified on a IR spectroscopy?

both contain C=O group

strong sharp peak

~1700cm-1

how can carboxylic acids be identified on a IR spectroscopy?

C=O peak at ~1700 cm⁻¹ (sharp)
• O–H peak at 2500–3300 cm⁻¹ (very broad)

How is infrared spectroscopy used to monitor air pollution and in breathalysers?

IR spectroscopy detects gases by their characteristic absorption peaks.

• Used to detect pollutants like CO and NO in the atmosphere
• Used in breathalysers to detect alcohol (ethanol) via O–H absorption

Each gas has a unique IR fingerprint, allowing identification and monitoring.