Flashcards in 17.2 - Infrared Spectroscopy Deck (9)
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1
What happens when covalent bonds absorb IR radiation?
- Covalent bonds contain energy and naturally vibrate
- Absorption of IR makes them vibrate in 2 ways - bending or stretching.
2
What happens during bending or stretching of bonds?
Stretch - rhythmic movement that increases or decreases the distance between the 2 atomic centres
Bending - change in bond angle
3
What does the amount a bond bends or stretches depend on?
- Atom's mass in bond - heavier=more vibration
- Bond strength - the stronger the bond the fast the vibration
4
How much radiation can a bond absorb?
Any bond can absorb as much radiation that has the same frequency as its natural frequency.
5
How do chemists measure the absorption of IR?
Frequency values are too large, so the reciprocal is used which is = to wave number
6
How are IR and atmospheric gases linked?
- Sun's IR is absorbed by Earth
- Some IR is re-emitted in the form of longer wavelengths
- H2O, CH4, CO2 (greenhouse gases) absorb these wavelengths and re-emit this energy as radiation > cause for global warming as it heats up the Earth.
7
What is the purpose and process of Infrared Spectroscopy (for organic molecules)?
- Used to identify functional groups
1. Place sample in IR spectrometer
2. Fire IR beam at 200-4000cm^-1 at sample
3. Molecule absorbs some of IR and re-emits that beam - it is analysed to identify the absorbed frequencies
4. Graphs plotted of transmittance against wavenumber.
8
What is the fingerprint region?
<1500cm^-1 on an infrared spectrum is known as the fingerprint region
- It contains unique peaks that are used to identify a particular molecules by comparing to a booklet of published spectrums or by a computer.
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